André Zimmermann

Zusammenfassung

Autonomous driving is a key vehicle capability for future mobility solutions that relies on the reliability of its high-performance vehicle computer. As for any electronics for automotive applications, thermal management is a crucial point. A very extensively employed approach for improving heat removal is the usage of heat spreaders in the form of a package lid, especially for flip-chip applications. The usage of a lid in flip-chip ball grid array (BGA) packages improves heat removal based on the heat spreading capabilities of the lid, and reduces package warpage, since with a lid the package becomes stiffer. However, adding a lid also increases stresses at solder interconnects. When selecting a material for the lid, the most intuitive criterion is to focus on the material’s thermal conductivity. Sometimes overlooked, the coefficient of thermal expansion (CTE) of the lid also plays an important role regarding package warpage and reliability of thermal interface materials (TIM) as well as solder interconnects, such as solder bumps. This work focuses on the influence of different lid materials at package level for flip-chip applications. Consequently, the influence of three alternative materials is investigated and compared to the performance of a standard copper lid. For the quantification of the effects, a validated finite element model of a flip-chip package is presented, with the thermo-mechanical performance of the studied lid materials validated based on package warpage, peel strains and plastic strain energy density at the bumps, as well as on peel and shear strains at the TIM.

Zusammenfassung

Autonomous driving is a key vehicle capability for future mobility solutions that relies on the reliability of its high-performance vehicle computer. As for any electronics for automotive applications, thermal management is a crucial point. A very extensively employed approach for improving heat removal is the usage of heat spreaders in the form of a package lid, especially for flip-chip applications. The usage of a lid in flip-chip ball grid array (BGA) packages improves heat removal based on the heat spreading capabilities of the lid, and reduces package warpage, since with a lid the package becomes stiffer. However, adding a lid also increases stresses at solder interconnects. When selecting a material for the lid, the most intuitive criterion is to focus on the material’s thermal conductivity. Sometimes overlooked, the coefficient of thermal expansion (CTE) of the lid also plays an important role regarding package warpage and reliability of thermal interface materials (TIM) as well as solder interconnects, such as solder bumps. This work focuses on the influence of different lid materials at package level for flip-chip applications. Consequently, the influence of three alternative materials is investigated and compared to the performance of a standard copper lid. For the quantification of the effects, a validated finite element model of a flip-chip package is presented, with the thermo-mechanical performance of the studied lid materials validated based on package warpage, peel strains and plastic strain energy density at the bumps, as well as on peel and shear strains at the TIM.

Zusammenfassung

Nowadays, there is a growing demand for structures in the micrometer and submicrometer regime for electrochemical and optical applications to fabricate circuit paths or optical gratings. Therefore, the aim of this work is to show the applicability of a simple and inexpensive method to manufacture micrometer- and submicrometer structures of ultrathin metal coatings on polymer substrates of cyclic olefin copolymer (COP) as well as on glass using maskless photolithography followed by lift-off. To enhance the adhesion of the photoresist on the polymer substrates surface pretreatments of the polymer substrates, e.g., by glow discharge or atmospheric plasma treatment were executed. The lithography process was carried out using a sprayed negative photoresist on glass and COP substrates exposed to ultraviolet light via a micromirror assay and without a mask. Based on the exposure limit and an initial proof of concept, gratings with a line width of 100 µm and a period of 200 µm were manufactured. After development, no adhesion layers were applied to facilitate fabrication and minimize costs. Thus, the substrates were sputtered with 50 nm gold layers, which were lifted off with acetone. During the processing, the factors influencing the accuracy of the structures, such as prebake, postbake and development parameters, were determined and an optimal parameter setting was derived.

Zusammenfassung

The demand for individualized products is continuously increasing. For this purpose, product development processes are already established in companies. However, these processes are typically based on mass products and are not necessarily suitable for individualized products. Hence, the question emerges of how to develop and manufacture individualized products in a corporate product development setup. The characteristics of individualized products and a multiple-case study in seven companies made apparent that product development processes for complex individualized products should be adapted according to the specific requirements and relate to specific product development methods. More specifically, results indicate that a prior definition and assurance of boundaries as well as free spaces through pretested products is key, as the validation stage is constrained for such products. Methods such as in-process monitoring, postprocessing, and responsibility sharing (co-design) and the use of expert tools foster such product development processes. That gives practitioners the possibility to develop and manufacture individualized products efficiently by adapting the product development process and using the right methods. Based on these results and the literature review, we propose a novel definition of individualized products and a holistic product development process that may support discussions of the relevance of mass individualization as a new paradigm.

Zusammenfassung

Inkjet printing for printed electronics is a growing market due to its advantages, including scalability, various usable materials and its digital, pixel based layout design. An important quality factor is the wetting of the ink on the substrate. This article proposes a workflow to evaluate the print quality of specific layouts by means of image analysis. A self-developed image analysis software, which compares a mask with the actual layout, enables a pixel-based analysis of the wetting behavior by the implementation of two parameters called over- and underwetting rate. A comparison of actual and targeted track widths can be performed for the evaluation of different parameters, such as the tested plasma treatment, drop spacing (DS) and substrate temperature. To prove the functionality of the image analyses tool, the print quality of Au structures inkjet printed on cyclic olefin copolymer (COC) substrates was studied experimentally by varying the three previously mentioned parameters. The experimental results showed that the wetting behavior of Au ink deposited on COC substrates influences various line widths differently, leading to higher spreading for smaller line widths. The proposed workflow is suitable for identifying and evaluating multiple tested parameter variations and might be easily adopted for printers for in-process print quality control in industrial manufacturing.

Zusammenfassung

This work is concerned with the examination of one-dimensional stress effects in mode-split, open-loop MEMS gyroscopes with the goal to predict the sensitivity change under printed circuit board (PCB) bending stress. Measurements with ten triaxial gyroscopes are compared to simulation results based on a detailed analytical model. The dependencies of gap distance and overlap of the in- and out-of-plane detection capacitances related to bending stress are formulated. Sensitivity change is predicted with 75% accuracy and the sign of gradient is correct for all measurements. Besides the change in geometry parameters of capacitances the effects of mechanical bending stress on the entire system are discussed. The purpose of the paper is to show the fundamental relationships on which all further considerations regarding MEMS gyroscopes under PCB stress are built.

Zusammenfassung

Hard coatings can be applied onto microstructured molds to influence wear, form filling and demolding behaviors in microinjection molding. As an alternative to this conventional manufacturing procedure, “direct processing” of physical-vapor-deposited (PVD) hard coatings was investigated in this study, by fabricating submicron features directly into the coatings for a subsequent replication via molding. Different diamondlike carbon (DLC) and chromium nitride (CrN) PVD coatings were investigated regarding their suitability for focused ion beam (FIB) milling and microinjection molding using microscope imaging and areal roughness measurements. Each coating type was deposited onto high-gloss polished mold inserts. A specific test pattern containing different submicron features was then FIB-milled into the coatings using varied FIB parameters. The milling results were found to be influenced by the coating morphology and grain microstructure. Using injection–compression molding, the submicron structures were molded onto polycarbonate (PC) and cyclic olefin polymer (COP). The molding results revealed contrasting molding performances for the studied coatings and polymers. For CrN and PC, a sufficient replication fidelity based on AFM measurements was achieved. In contrast, only an insufficient molding result could be obtained for the DLC. No abrasive wear or coating delamination could be found after molding.

Zusammenfassung

Die Benetzung von Schmelze-berührenden Maschinenkomponenten sowie die Anhaftung von erstarrtem Kunststoff auf dem Formwerkzeug basiert auf Wechselwirkungen an der Grenzfläche zwischen Kunststoff und Werkzeugmaterial. Ein Ansatz zur Charakterisierung der Benetzbarkeit von Festkörperoberflächen ist die Bestimmung der freien Oberflächenenergie auf Basis von Kontaktwinkelmessungen. Bisherige Studien ermittelten die freie Oberflächenenergie von verschiedenen Hartstoffschichten meist durch Kontaktwinkelmessungen bei Raumtemperatur oder basierend auf einem statischen Messverfahren, welches nahezu keine Reproduzierbarkeit aufweist. Um die Benetzbarkeit von Hartstoffschichten für die Kunststoffverarbeitung zu bewerten, wurden in dieser Studie dynamische Kontaktwinkelmessungen von zwei Prüfflüssigkeiten auf poliertem Stahl sowie einer Titannitrid- (TiN), zwei Chromnitrid- (CrN) und einer amorphen Kohlenstoffbeschichtung (a-C:H:Si) im Entformungstemperaturbereich von 60 °C bis 140 °C durchgeführt. Anschließend wurden die freien Oberflächenenergien der Beschichtungen für den betrachteten Temperaturbereich nach der Methode von Owens, Wendt, Rabel und Kaelble bestimmt. Die Ergebnisse zeigen, dass die CrN-Beschichtungen die geringste freie Oberflächenenergie aufweisen. Im Vergleich zeigte sich für alle Hartstoffschichten eine Abnahme der freien Oberflächenenergie mit sich erhöhender Temperatur. Die chemische Zusammensetzung der Probenoberfläche scheint bei gleichbleibenden Messbedingungen für glatte Oberflächen der bestimmende Faktor für die Höhe der freien Oberflächenenergie zu sein. The wetting of melt-facing surfaces as well as the sticking of solidified plastic on molding tools is related to surface effects between plastic materials and mold material. One approach to quantify the wetting on solid surfaces is the determination of the free surface energy. Several studies determined the free surface energy of hard coatings used in polymer processing based on the drop shape analysis. These measurements were, however, mostly conducted at room temperature, which is not comparable to molding temperatures, or were limited to static contact angle measurements, which are nearly non-reproducible. In this study, the wetting of hard coatings used in polymer processing was investigated by measuring the advancing contact angle of two test fluids on a titanium nitride, two differently deposited chromium nitride and one diamond-like carbon coating at relevant demolding temperatures in the range from 60 °C to 140 °C. The results showed the smallest free surface energy values for the two chromium nitride coatings. The comparison of all investigated coatings revealed a decline of the free surface energy with increasing solid temperature. The chemical composition of the material seems to be a determining factor for smooth surfaces and constant measuring conditions.

Zusammenfassung

The demolding of plastic parts remains a challenging aspect of injection molding. Despite various experimental studies and known solutions to reduce demolding forces, there is still not a complete understanding of the effects that occur. For this reason, laboratory devices and in-process measurement injection molding tools have been developed to measure demolding forces. However, these tools are mostly used to measure either frictional forces or demolding forces for a specific part geometry. Tools that can be used to measure the adhesion components are still the exception. In this study, a novel injection molding tool based on the principle of measuring adhesion-induced tensile forces is presented. With this tool, the measurement of the demolding force is separated from the actual ejection step of the molded part. The functionality of the tool was verified by molding PET specimens at different mold temperatures, mold insert conditions and geometries. It was demonstrated that once a stable thermal state of the molding tool was achieved, the demolding force could be accurately measured with a comparatively low force variance. A built-in camera was found to be an efficient tool for monitoring the contact surface between the specimen and the mold insert. By comparing the adhesion forces of PET molded on polished uncoated, diamond-like carbon and chromium nitride (CrN) coated mold inserts, it was found that a CrN coating reduced the demolding force by 98.5% and could therefore be an efficient solution to significantly improve demolding by reducing adhesive bond strength under tensile loading.

Zusammenfassung

Die kostengünstige Herstellung von Hybridoptiken kann durch die Replikation eines mikrostrukturierten Werkzeugeinsatzes mittels Spritzprägen realisiert werden. Das Werkzeug wird mittels Laserlithografie und anschließender galvanischer Abformung hergestellt. Im Vordergrund dieses Herstellungsverfahrens liegt die Verbesserung der Lagetoleranz zwischen der diffraktiven und refraktiven Fläche.

Zusammenfassung

The research presented in this work compensates non-orthogonality over temperature stress effects in low-cost open-loop MEMS gyroscopes using neural networks (NN) for a sensor individual compensation to improve the sensor performance. The non-orthogonality is included in the sensor cross-axis sensitivity (CAS) of MEMS gyroscopes. Using the model-agnostic meta-learning algorithm (MAML) as a self-calibration algorithm and one initial measurement after soldering, an individual compensation model is generated for each sensor that predicts the non-orthogonality using the MEMS gyroscope's quadrature value as an input. It will be shown that a sensor-individual model outperforms a compensation model that should fit for all sensors at once like linear regression or classic NN and improves the non-orthogonality by 82.7 %, 7.5 % and 70 % for yx-, zx-, and zy-non-orthogonality,

Zusammenfassung

Fiber optic Sagnac interferometer can measure the rotation rate of a system with a high sensitivity. However, they require a large sensor area which leads to a huge footprint and size compared to their MEMS counterpart. Consequently, the performance decreases when using chip integrated Sagnac interferometers with small sensor areas. Here, we address this issue and present a method to improve the sensitivity at a small scale. Therefore, we utilize twomode squeezed light that can be generated in a ring resonator via four-wave mixing (FWM), which can have a very low noise. We show that the combination of classical coherent light and squeezed light can improve the sensor performance compared to a classical fiber optic Sagnac interferometer. For this purpose, we discuss two different configurations that are suited for various applications. The first one makes use of the low-noise of squeezed light and is suited for small and low loss systems using intensitiy difference (ID) measurements while the second one measures the variance of squeezed light via product detection (PD) and is suited for larger and lossy systems.

Zusammenfassung

Increasing demands for precision electronics require individual components such as resistors to be specified, as they can be the limiting factor within a circuit. To specify quality and long-term stability of resistors, noise measurements are a common method. This review briefly explains the theoretical background, introduces the noise index and provides an insight on how this index can be compared to other existing parameters. It then focuses on the different methods to measure excess noise in resistors. The respective advantages and disadvantages are pointed out in order to simplify the decision of which setup is suitable for a particular application. Each method is analyzed based on the integration of the device under test, components used, shielding considerations and signal processing. Furthermore, our results on the excess noise of resistors and resistor networks are presented using two different setups, one for very low noise measurements down to 20 µHz and one for broadband up to 100 kHz. The obtained data from these measurements are then compared to published data. Finally, first measurements on commercial strain gauges and inkjet-printed strain gauges are presented that show an additional 1/fα component compared to commercial resistors and resistor networks.

Zusammenfassung

This work is motivated by the rarely available material data for thermosets and a missing inline viscosity measurement method to monitor melt property deviations. A nozzle viscometer is designed for inline viscosity measurement of phenol-formaldehyde compounds. The nozzle viscometer is mounted at the plasticizing unit of an injection molding machine. A fluid coolant circuit allows a dynamic tempering to pause the transient crosslinking reaction. A 2D FDM model is implemented, to calculate the viscous heating within an injection cycle and to compensate the temperature rising effect in the viscosity measurement. The FDM model processes the inline sensor signals in a closed loop correction in real time to determine a corrected reactive viscosity model. The signal-to-noise-ratio quantifies the reliability of the inline viscosity measurement method.

Zusammenfassung

LDS-MIDs (laser direct structured mechatronic integrated devices) are 3D (three-dimensional) circuit carriers that are used in many applications with a focus on antennas. However, thanks to the rising frequencies of HF (high-frequency) systems in 5G and radar applications up to the mmWave (millimeter wave) region, the requirements regarding the geometrical accuracy and minimal wall thicknesses for proper signal propagation in mmWave circuits became more strict. Additionally, interest in combining those with 3D microstructures like trenches or bumps for optimizing transmission lines and subsequent mounting processes is rising. The change from IM (injection molding) to ICM (injection compression molding) could offer a solution for improving the 3D geometries of LDS-MIDs. To enhance the scientific insight into this process variant, this paper reports on the manufacturing of LDS-MIDs for mmWave applications. Measurements of the warpage, homogeneity of local wall thicknesses, and replication accuracy of different trenches and bumps for mounting purposes are presented. Additionally, the effect of a change in the manufacturing process from IM to ICM regarding the dielectric properties of the used thermoplastics is reported as well as the influence of ICM on the properties of LDS metallization—in particular the metallization roughness and adhesion strength. This paper is then concluded by reporting on the HF performance of CPWs (coplanar waveguides) on LDS-MIDs in comparison to an HF-PCB.

Zusammenfassung

Mechatronic Integrated Devices or Molded Interconnect Devices (MID) are three-dimensional (3D) circuit carriers. They are mainly fabricated by laser direct structuring (LDS) and subsequent electroless copper plating of an injection molded 3D substrate. Such LDS-MID are used in many applications today, especially antennas. However, in high frequency (HF) systems in 5G and radar applications, the demand on 3D circuit carriers and antennas increases. Electroless copper, widely used in MID, has significantly lower electrical conductivity compared to pure copper. Its lower conductivity increases electrical loss, especially at higher frequencies, where signal budget is critical. Heat treatment of electroless copper deposits can improve their conductivity and adhesion to the 3D substrates. This paper investigates the effects induced by tempering processes on the metallization of LDS-MID substrates. As a reference, HF Printed Circuit Boards (PCB) substrates are also considered. Adhesion strength and conductivity measurements, as well as permittivity and loss angle measurements up to 1 GHz, were carried out before and after tempering processes. The main influencing factors on the tempering results were found to be tempering temperature, atmosphere, and time. Process parameters like the heating rate or applied surface finishes had only a minor impact on the results. It was found that tempering LDS-MID substrates can improve the copper adhesion and lower their electrical resistance significantly, especially for plastics with a high melting temperature. Both improvements could improve the reliability of LDS-MID, especially in high frequency applications. Firstly, because increased copper adhesion can prevent delamination and, secondly, because the lowered electrical resistance indicates, in accordance with the available literature, a more ductile copper metallization and thus a lower risk of microcracks.

Zusammenfassung

A new methodology for considering thermo-mechanical material property variability in virtual design of experiment (vDoE) studies is presented. For the estimation of the lower and upper bounds of the properties, theoretical models and relevant correlations between material properties are presented. The focus for the bounds definition is given to composite materials, i.e., a mixture of two or more homogeneous dissimilar materials, such as metal matrix composites (MMCs), ceramic matrix composites (CMC), etc. For not composite materials, alternative approaches for defining the bounds are discussed. To exemplify the implementation of the proposed methodology, a vDoE of a 2-D finite element (FE) thermo-mechanical model of an electronic package is presented, followed by a discussion regarding the influence of material property variability on the model’s thermo-mechanical responses.

Zusammenfassung

Thermosonic wire bonding is a well-established process. However, when working on advanced substrate materials and the associated required metallization processes to realize innovative applications, multiple factors impede the straightforward utilization of the known process. Most prominently, the surface roughness was investigated regarding bond quality in the past. The practical application of wire bonding on difficult-to-bond substrates showed inhomogeneous results regarding this quality characteristic. This study describes investigations on the correlation among the surface roughness, profile peak density and bonding quality of Au wire bonds on thermoplastic and thermoset-based substrates used for high-frequency (HF) applications and other high-end applications. FR4 PCB (printed circuit board flame resitant class 4) were used as references and compared to HF-PCBs based on thermoset substrates with glass fabric and ceramic filler as well as technical thermoplastic materials qualified for laser direct structuring (LDS), namely LCP (liquid crystal polymer), PEEK (polyether ether ketone) and PTFE (polytetrafluoroethylene). These LDS materials for HF applications were metallized using autocatalytic metal deposition to enable three-dimensional structuring, eventually. For that purpose, bond parameters were investigated on the mentioned test substrates and compared with state-of-the-art wire bonding on FR4 substrates as used for HF applications. Due to the challenges of the limited thermal conductivity and softening of such materials under thermal load, the surface temperatures were matched up by thermography and the adaptation of thermal input. Pull tests were carried out to determine the bond quality with regard to surface roughness. Furthermore, strategies to increase reliability by the stitch-on-ball method were successfully applied.

Zusammenfassung

The use of focused ion and focused electron beam (FIB/FEB) technology permits the fabrication of micro- and nanometer scale geometries. Therefore, FIB/FEB technology is a favorable technique for preparing TEM lamellae, nanocontacts, or nanowires and repairing electronic circuits. This work investigates FIB/FEB technology as a tool for nanotip fabrication and quantum mechanical tunneling applications at a low tunneling voltage. Using a gas injection system (GIS), the Ga-FIB and FEB technology allows both additive and subtractive fabrication of arbitrary structures. Using energy dispersive X-ray spectroscopy (EDX), resistance measurement (RM), and scanning tunneling microscope (STM)/spectroscopy (STS) methods, the tunneling suitability of the utilized metal–organic material–platinum carbon (PtC) is investigated. Thus, to create electrode tips with radii down to 15 nm, a stable and reproducible process has to be developed. The metal–organic microstructure analysis shows suitable FIB parameters for the tunneling effect at high aperture currents (260 pA, 30 kV). These are required to ensure the suitability of the electrodes for the tunneling effect by an increased platinum content (EDX), a low resistivity (RM), and a small band gap (STM). The STM application allows the imaging of highly oriented pyrolytic graphite (HOPG) layers and demonstrates the tunneling suitability of PtC electrodes based on high FIB aperture currents and a low tunneling voltage.

Zusammenfassung

In micro-electro-mechanical systems (MEMS) testing high overall precision and reliability are essential. Due to the additional requirement of runtime efficiency, machine learning methods have been investigated in recent years. However, these methods are often associated with inherent challenges concerning uncertainty quantification and guarantees of reliability. The goal of this paper is therefore to present a new machine learning approach in MEMS testing based on Bayesian inference to determine whether the estimation is trustworthy. The overall predictive performance as well as the uncertainty quantification are evaluated with four methods: Bayesian neural network, mixture density network, probabilistic Bayesian neural network and BayesFlow. They are investigated under the variation in training set size, different additive noise levels, and an out-of-distribution condition, namely the variation in the damping factor of the MEMS device. Furthermore, epistemic and aleatoric uncertainties are evaluated and discussed to encourage thorough inspection of models before deployment striving for reliable and efficient parameter estimation during final module testing of MEMS devices. BayesFlow consistently outperformed the other methods in terms of the predictive performance. As the probabilistic Bayesian neural network enables the distinction between epistemic and aleatoric uncertainty, their share of the total uncertainty has been intensively studied.

Zusammenfassung

Micro-electro-mechanical systems (MEMS) are of great importance in a broad range of applications including vehicle safety and consumer electronics. During the testing of these devices, large heterogeneous data sets containing a variety of parameters are recorded. Aiming to substitute costly measurements as well as to gain insight into the relations among the measured parameters, graph neural networks (GNNs) are investigated. Thus, the questions are addressed whether for inference of MEMS final module level test parameters, working on graph structures leads to an improvement of the predictive performance compared to the analysis via standard machine learning approaches on tabular data and how the graph structure and learning algorithm contribute to the overall performance. To evaluate this, in an empirical study different graph representations of the acquired test data were set up. On these, four different state-of-the-art GNN architectures were trained and compared on the task of raw sensitivity prediction for a MEMS gyroscope. Whereas the GNNs performed on par with a light gradient boosting machine, neural network and multivariate adaptive regression splines model used as baseline on the complete data set, in the presence of sparse data, the GNNs outperformed the baseline methods in terms of the overall root-mean-square error (RMSE) and achieved distinct improvement in the maximum error when trained on data with similar sparsity rates as observed during the validation.

Zusammenfassung

Microelectromechanical devices are known to be sensitive to ambient humidity. This is especially true for devices in moisture sensitive plastic packages such as consumer targeted inertial measurement units. Stress and deformation based effects are shown to be a main contributor to humidity related effects such as performance and offset drifts. This paper shows that stress sensing units embedded in the mechanically coupled electronic control circuitry can be utilized to detect and compensate stress based humidity performance drifts of plastic packaged inertial measurement units. Next to the utilized stress sensor cells themselves a compensation approach is presented, that corrects the humidity based scale factor drift of a MEMS angular rate sensor while a humidity load is applied. This is achieved by finding a symbolic compensation function, which predicts the moisture induced scale factor drift, based only on the stress values within the electronic control circuitry, utilizing genetic symbolic regression. It is demonstrated that, using stress sensors, the humidity induced scale factor drift of two different gyroscope core types can be reduced by a factor of 3, which holds true for parts coming from separate assembly lots. 2022-0013

Zusammenfassung

Encapsulated microelectromechanical measurement units are known to be sensitive to ambient humidity conditions, due to various effects caused by moisture diffusing into and out of the plastic packaging components. This paper focuses on investigating the effect that a change of moisture content has on the transient offset behavior of a packaged MEMS sensor by investigating the output signals of several test devices that only differ in their response to deformation of the MEMS core area. This comprises a novel method of experimentally analyzing the transient drift behavior of a MEMS caused by a deformation of the MEMS core area. This approach enables a back calculation of possible deformation shapes of the core area that explain the observed offset drifts in a given package. It was shown that the humidity response of a MEMS sensor is a strongly transient function that is not proportional to the uptake of water and can therefore significantly differ from their humidity performance at or close to a saturated state. Humidity performance tests that take only this state as point of reference for a performance evaluation cannot correctly estimate the humidity induced offset drifts. It was also shown that the moisture induced offset drifts can be traced back to a superposition of several deformation fields leading to several stages of the humidity response of MEMS sensors. Based on the example of the test devices it was shown that MEMS cores can be optimized to minimize the response of moisture effects. 2021-0212

Zusammenfassung

Digitally printed conductive structures often need to be electrically connected to batteries, microcontrollers, or other devices. A consensus of industry and research is that such hybrid printed electronics will play a major part in the future of printed electronics. To promote the technology of hybrid printed electronics, surface mount technologies for electronic components using isotropic conductive adhesives (ICAs) and low melting tin bismuth solders on inkjet-printed silver structures on injection molded liquid crystal polymer (LCP) substrates were investigated in this publication. The special needs for inkjet-printed electronics were considered as well as the reliability of assembled surface mounted devices (SMDs) and their failure mechanisms. Connected 0603 and 1206 SMD components achieved a characteristic fatigue life of more than 3500 cycles during thermal cycling at +125 °C/−40 °C and withstood over 1000 h under a damp-heat atmosphere of +85 °C/85% RH. The coefficient of thermal expansion (CTE) of the substrate and the selection of solder have major impacts on the reliability of the assemblies.

Zusammenfassung

This paper describes the characterization of inkjet-printed resistive temperature sensors according to the international standard IEC 61928-2. The goal is to evaluate such sensors comprehensively, to identify important manufacturing processes, and to generate data for inkjet-printed temperature sensors according to the mentioned standard for the first time, which will enable future comparisons across different publications. Temperature sensors were printed with a silver nanoparticle ink on injection-molded parts. After printing, the sensors were sintered with different parameters to investigate their influences on the performance. Temperature sensors were characterized in a temperature range from 10 °C to 85 °C at 60% RH. It turned out that the highest tested sintering temperature of 200 °C, the longest dwell time of 24 h, and a coating with fluoropolymer resulted in the best sensor properties, which are a high temperature coefficient of resistance, low hysteresis, low non-repeatability, and low maximum error. The determined hysteresis, non-repeatability, and maximum error are below 1.4% of the full-scale output (FSO), and the temperature coefficient of resistance is 1.23–1.31 × 10−3 K−1. These results show that inkjet printing is a capable technology for the manufacturing of temperature sensors for applications up to 85 °C, such as lab-on-a-chip devices.

Zusammenfassung

High quality and long product life are two fundamental requirements for all circuit carriers, including molded interconnect devices (MID), to find application in various fields, such as automotive, sensor technology, medical technology, and communication technology. When developing a MID for a certain application, not only the design, but also the choice of material as well as the process parameters need to be carefully considered. A well-established method to evaluate the lifetime of such MID, respective of their conductor tracks, is the thermal shock test, which induces thermomechanical stresses upon cycling. Even though this method has numerous advantages, one major disadvantage is its long testing time, which impedes rapid developments. Addressing this disadvantage, this study focuses on the laser direct structuring of thermoplastic LCP Vectra E840i LDS substrates and the subsequent electroless metallization of the commonly used layer system Cu/Ni/Au to force differences in the conductor tracks’ structure and composition. Performing standardized thermal shock tests alongside with flexural fatigue tests, using a customized setup, allows comparison of both methods. Moreover, corresponding thermomechanical simulations provide a direct correlation. The flexural fatigue tests induce equivalent or even higher mechanical stresses at a much higher cycling rate, thus drastically shorten the testing time.

Zusammenfassung

Hard coatings can be applied onto microstructured molds to influence wear, form filling and demolding behaviors in microinjection molding. As an alternative to this conventional manufacturing procedure, “direct processing” of physical-vapor-deposited (PVD) hard coatings was investigated in this study, by fabricating submicron features directly into the coatings for a subsequent replication via molding. Different diamondlike carbon (DLC) and chromium nitride (CrN) PVD coatings were investigated regarding their suitability for focused ion beam (FIB) milling and microinjection molding using microscope imaging and areal roughness measurements. Each coating type was deposited onto high-gloss polished mold inserts. A specific test pattern containing different submicron features was then FIB-milled into the coatings using varied FIB parameters. The milling results were found to be influenced by the coating morphology and grain microstructure. Using injection–compression molding, the submicron structures were molded onto polycarbonate (PC) and cyclic olefin polymer (COP). The molding results revealed contrasting molding performances for the studied coatings and polymers. For CrN and PC, a sufficient replication fidelity based on AFM measurements was achieved. In contrast, only an insufficient molding result could be obtained for the DLC. No abrasive wear or coating delamination could be found after molding.

Zusammenfassung

The assembly of passive components on flexible electronics is essential for the functionalization of circuits. For this purpose, adhesive bonding technology by isotropic conductive adhesive (ICA) is increasingly used in addition to soldering processes. Nevertheless, a comparative study, especially for bending characterization, is not available. In this paper, soldering and conductive adhesive bonding of 0603 and 0402 components on flexible polyimide substrates is compared using the design of experiments methods (DoE), considering failure for shear strength and bending behavior. Various solder pastes and conductive adhesives are used. Process variation also includes curing and soldering profiles, respectively, amount of adhesive, and final surface metallization. Samples created with conductive adhesive H20E, a large amount of adhesive, and a faster curing profile could achieve the highest shear strength. In the bending characterization using adhesive bonding, samples on immersion silver surface finish withstood more cycles to failure than samples on bare copper surface. In comparison, the samples soldered to bare copper surface finish withstood more cycles to failure than the soldered samples on immersion silver surface finish.

Zusammenfassung

Microsystems and interconnect devices based on ceramic substrate materials are used in many high temperature and power applications due to their superior thermal properties. With the current state-of-the-art pro-cesses, such as direct-bonded copper or high/low temperature co-fired ceramics, only 2D or multilayer struc-tures can be realized. In this paper, we present a fully digital, selective and additive process chain based on direct laser-induced activation and subsequent autocatalytic metallization of injection molded Al2O3-based substrates to produce 3D-ceramic interconnect devices. In order to laser-activate the Al2O3, it has either to be sintered in H2 atmosphere or doped with Cr2O3. The resulting selective metallization shows an adhesive strength of up to 50 N/mm² and can be connected with common interconnection technologies, such as reflow soldering, wire bonding etc. Thus, the developed process chain offers new possibilities in ceramic circuit carrier design and the integration into complex microsystems.

Zusammenfassung

Integrating electrical functionality during additive manufacturing (AM) is a promising new field of application. In this article, different concepts for combining an extrusion-based AM process called 3-D dispensing (3DD) with the embedding of electrical components are developed and compared. Based on criteria, such as resulting surface quality or overall accuracy, the best strategy among six different approaches is identified. To further validate and confirm the choice, long-term reliability tests humidity and thermal shock testing (TST) with a particular focus on the electrical contacts between the printed tracks and the embedded electronic components have been conducted. It was shown that the embedding strategy and the cavity design have no influence on the long-term properties of the printed electrical tracks. Finally, an acceleration sensor is embedded in a 3-D housing to prove real use-case applicability and to show the improvements identified in the previous study.

Zusammenfassung

The influence of parametric nonlinearities on the mode matching of closed-loop operated MEMS gyroscopes is investigated. Accurate resonance tuning of mechanical detection modes is essential for optimal noise suppression in closed-loop resonators. Large deflections of the drive mode lead to a geometric nonlinearity, which induces a phase-dependency in the mode-matching procedure. Those effects are known to amplify signal-to-noise ratio in open-loop vibratory MEMS gyroscopes. Predicted and measured tuning voltages and folded response of a sense mode in a prototype gyroscope are compared. Using simulations, it is shown that the pilottone with a 90° phase can confine the crosstalk of the Coriolis and quadrature channel to the quadrature channel exclusively. When applying a quadrature compensation in the simplified model, nonlinear amplification is prohibited in the output channel even for low gain of the force-to-rebalance loop. Furthermore, it is shown that in a simulation with idealized drive motion and demodulation signals the cross-coupling nonlinearity by itself does not have a major impact on standard noise suppression capabilities. 2021-0232

Zusammenfassung

Todays continuous improvement and advancement in the injection molding process for plastics allow for increasing reliability of the process parameter control, whereas the fluctuations of the material properties still present a great challenge. To compensate for these fluctuations, a nozzle capillary rheometer is developed with the aim to determine the viscosity inline during the injection process in series production applications. An essential part of this work is the signal processing and the definition of a suitable integration boundary to ensure a reliable signal evaluation. In addition, based on mathematical modeling and established correction factors, it is possible to determine the effective viscosity accurately without the need to replace the capillary channel according to the Bagley correction.

Zusammenfassung

Nowadays, digital printing technologies such as inkjet and aerosol jet printing are gaining more importance since they have proven to be suitable for the assembly of complex microsystems. This also applies to medical technology applications like hearing aids where patient-specific solutions are required. However, assembly is more challenging than with conventional printed circuit boards in terms of material compatibility between substrate, interconnect material and printed ink. This paper describes how aerosol jet printing of nano metal inks and subsequent assembly processes are utilized to connect electrical components on 3D substrates fabricated by Digital Light Processing (DLP). Conventional assembly technologies such as soldering and conductive adhesive bonding were investigated and characterized. For this purpose, curing methods and substrate pretreatments for different inks were optimized. Furthermore, the usage of electroless plating on printed metal tracks for improved solderability was investigated. Finally, a 3D ear mold substrate was used to build up a technology demonstrator by means of conductive adhesives.

Zusammenfassung

The development and manufacturing of high-precision micro-mechatronic systems (MMS) is a challenging task, and the high demand for individualized products complicates the engineering design process (EDP) in particular. The established EDP for MMS is not designed for individualized products. This article gives an overview of the challenges (critical factors) in product development and manufacturing of individualized MMS (iMMS), a novel definition of iMMS, and describes a new qualitative methodology in order to tailor an EDP based on use cases, so-called “Tailored EDP-Methodology” (TEDP-Methodology). This TEDP-Methodology allows creating use-case-based product groups through the abstraction of the use cases and evaluating the requirements, which is essential to tailor or develop a new EDP. For the development of this new approach, a literature review and qualitative content analysis are prefaced. The TEDP-Methodology is critically examined and validated with a real case study for the development and manufacturing of an iMMS. This study shows critical points within the EDP. It shows fields of action for innovative tools to support the development process of iMMS and requirements for different product groups within iMMS. This article has both theoretical and practical implications.

Zusammenfassung

Diese Arbeit beschreibt die Entwicklung eines mikro-integrierten multispektralen Bildgebungssystems für die hyper-spektrale Bildgebung (HSI). Ziel ist es, durch den Einsatz von polymeren optischen Komponenten die Integrations-dichte zu erhöhen, das Gewicht zu reduzieren und gleichzeitig die Funktionalität im Vergleich zu klassischen HSI-Ka-merasystemen zu verbessern. Wirtschaftlichen Vorteile einer vereinfachten Montage durch direkte Integration von Be-festigungselementen als auch die Möglichkeit der Massenproduktion von Polymeroptiken werden betrachtet. Eine Stra-tegie zur Integration in ein Kamerasystem wird entwickelt, welche die Anforderungen für die Mikromontage aller Kom-ponenten erfüllt. Es werden Methoden zur Mikromontage eines polymeren Mikrolinsenarrays (MLA) mit 12.000 Mikrolinsen in Bezug auf die Positionierung eines Charge-Coupled Device (CCD) Chips sowie eines Beugungsgitters ange-wendet. Die direkte Integration von Befestigungselementen in das MLA ermöglicht dabei eine ultrakompakte Montage mit einer reduzierten Anzahl von Montagevorgängen. Die Ausrichtung der Spektrallinien auf die CCD-Pixel ermöglicht die Optimierung der Anzahl der auf einem einzigen Chip abgebildeten Spektren. Die Funktionalität des Systems wird demonstriert und stellt eine technologische Verbesserung für eine Vielzahl von Anwendungen dar, die von der Verfüg-barkeit eines solchen Systems in Bezug auf Einfachheit, Kosten, Größe und Gewicht profitieren können. This work describes the development of a micro-integrated multi-spectral imaging system for hyperspectral imaging (HSI). The aim is to employ polymeric optical components to increase integration density and reduce weight while provid-ing improved functionality compared to classical HSI camera systems. Economic advantages of both, simplified assembly by direct integration of mounting features and the ability of mass production of polymer optics are being addressed. An integration strategy into a camera system is developed, providing the required features for micro-assembly of all compo-nents. Methods for micro assembly of a polymeric microlens array (MLA) with 12.000 micro lenses in relation to the positioning of a Charge-Coupled Device (CCD) chip as well as a diffraction grating are applied. The direct integration of mounting features into the MLA allows for ultra-compact assembly with a reduced number of assembly processes. Fur-thermore, it enables the alignment of spectral lines to the CCD pixels, thus optimizing the number of spectra mapped on a single chip. The functionality of system is demonstrated, presenting a technological improvement for a large variety of applications, which may profit from the availability of such a system in terms of simplicity, costs, size and weight.

Zusammenfassung

Most accelerometers today are based on the capacitive principle. However, further miniaturization for micro integration of those sensors leads to a poorer signal-to-noise ratio due to a small total area of the capacitor plates. Thus, other transducer principles should be taken into account to develop smaller sensors. This paper presents the development and realization of a miniaturized accelerometer based on the tunneling effect, whereas its highly sensitive effect regarding the tunneling distance is used to detect small deflections in the range of sub-nm. The spring-mass-system is manufactured by a surface micro-machining foundry process. The area of the shown polysilicon (PolySi) sensor structures has a size smaller than 100 µm × 50 µm (L × W). The tunneling electrodes are placed and patterned by a focused ion beam (FIB) and gas injection system (GIS) with MeCpPtMe3 as a precursor. A dual-beam system enables maximum flexibility for post-processing of the spring-mass-system and patterning of sharp tips with radii in the range of a few nm and initial distances between the electrodes of about 30–300 nm. The use of metal–organic precursor material platinum carbon (PtC) limits the tunneling currents to about 150 pA due to the high inherent resistance. The measuring range is set to 20 g. The sensitivity of the sensor signal, which depends exponentially on the electrode distance due to the tunneling effect, ranges from 0.4 pA/g at 0 g in the sensor operational point up to 20.9 pA/g at 20 g. The acceleration-equivalent thermal noise amplitude is calculated to be 2.4–3.4 mg/Hz. Electrostatic actuators are used to lead the electrodes in distances where direct quantum tunneling occurs.

Zusammenfassung

To realize quantum tunneling applications with movable electrodes, sharp tips with radii down to several tens of nanometers are necessary. The use of a focused ion beam (FIB) and focused electron beam (FEB) with a gas injection system (GIS) allows the integration of geometries in the nanoscale directly into micro and nano systems. However, the implementation of the tunneling effect clearly depends on the material. In this work, a metal-organic precursor is used. The investigation of the prepared tunneling electrodes enables an insight into FIB/FEB parameters for the realization of quantum tunneling applications. For this purpose, a high-resolution transmission electron microscopy (HRTEM) analysis is performed. The results show a dependence of the material nanostructure regarding platinum (Pt) grain size and distribution in an amorphous carbon matrix from the used beam and the FIB currents. The integration of the tips into a polysilicon (PolySi) beam and measuring the current signal by approaching the tips show significant differences in the results. Moreover, the approach of FEB tips shows a non-contact behavior even when the tips are squeezed together. The contact behavior depends on the grain size, proportion of platinum, and the amount of amorphous carbon in the microstructure, especially at the edge area of the tips. This study shows significant differences in the nanostructure between FIB and FEB tips, particularly for the FIB tips: The higher the ion current, the greater the platinum content, the finer the grain size, and the higher the probability of a tunneling current by approaching the tips.

Zusammenfassung

Electronic devices and their associated sensors are exposed to increasing mechanical, thermal and chemical stress in modern applications. In many areas of application, the electronics are completely encapsulated with thermosets in a single process step using injection molding technology, especially with epoxy molding compounds (EMC). The implementation of the connection of complete systems for electrical access through a thermoset encapsulation is of particular importance. In practice, metal pin contacts are used for this purpose, which are encapsulated together with the complete system in a single injection molding process step. However, this procedure contains challenges because the interface between the metallic pins and the plastic represents a weak point for reliability. In order to investigate the reliability of the interface, in this study, metallic pin contacts made of copper-nickel-tin alloy (CuNiSn) and bronze (CuSn6) are encapsulated with standard EMC materials. The metal surfaces made of CuNiSn are further coated with silver (Ag) and tin (Sn). An injection molding tool to produce test specimens is designed and manufactured according to the design rules of EMC processing. The reliability of the metal-plastic interfaces are investigated by means of shear and leak tests. The results of the investigations show that the reliability of the metal-plastic joints can be increased by using different material combinations.

Zusammenfassung

Geräteelektronik und dazugehörige Sensoren sind in modernen Anwendungen steigender mechanischer, thermischer und chemischer Beanspruchung ausgesetzt. Dabei werden die Elektroniken in vielen Anwendungsbereichen mit Duroplasten, im Speziellen mit Epoxidharzformmassen (Epoxy Moulding Compounds, EMC), in einem Prozessschritt mit dem Spritzgussverfahren vollständig verkapselt. Die Umsetzung der Ankontaktierung der Gesamtsysteme für den elektrischen Zugang von außen ins Innere einer Duroplastverkapselung ist von besonderer Bedeutung. In der Praxis kommen hierfür meist metallische Steckerkontakte zum Einsatz, die als Teilbereich eines Gesamtsystems im Spritzgussverfahren mit Kunststoff verkapselt werden. Jedoch bringt diese Vorgehensweise Herausforderungen mit sich, da die Schnittstelle zwischen den metallischen Steckerkontakten und dem Kunststoff eine Schwachstelle für die Zuverlässigkeit darstellt. So wurden im Rahmen der Untersuchungen metallische Steckerkontakte aus Kupfer-Nickel-Zinn-Legierung (CuNiSn) und Bronze (CuSn6) verwendet. Die Steckerkontakte aus CuNiSn wurden weiterführend mit Silber (Ag) und Zinn (Sn) beschichtet. Für die Abmusterung des Metall-Kunststoff-Verbundes wurde ein Spritzgusswerkzeug nach den Designregeln der EMC-Verarbeitung ausgelegt und hergestellt. Die Untersuchungen zur Zuverlässigkeit des Metall-Kunststoff-Verbundes erfolgte mittels Scherversuchen und Dichtheitsprüfung. Die Ergebnisse der Untersuchungen zeigen, dass durch den Einsatz verschiedener Materialkombinationen die Zuverlässigkeit der Metall-Kunststoff-Verbindungen erhöht werden kann.

Zusammenfassung

Parameter extraction during the final test of MEMS sensors poses a highly time-critical challenge. The progressing miniaturization, test stimuli and structural complexity lead to nonlinear couplings and inhomogeneity in system differential equations, which cannot be linearized and are therefore dependent on either slow numerical solution methods or machine learning algorithms requiring many labeled data. A transfer learning approach is presented making use of high complexity ASIC-MEMS models for Monte-Carlo generation of simulated devices, which are used to pre-train neural networks on the task of parameter extraction. In a first step, it is shown that for both, high quality factor and low quality factor systems, neural networks are not only able to fit the relation between time-series recorded during final testing and the two performance parameters natural frequency and damping factor but also to extract Brownian noise, mass, and epitaxial layer thickness. Subsequently, it is shown that the transfer learning approach is particularly useful for the determination of parameters, which cannot be measured directly during the final test and for which it is expensive to record labeled data like Brownian noise for systems in a harsh production test environment. If only very few labeled samples are available - in the performed experiments, 25 devices under test were sufficient - the transfer learning approach outperforms a neural network purely trained on measured data. These findings emphasize the practical advances of the transfer learning approach and motivate the evaluation of further applications in the field of parameter extraction in MEMS sensors.

Zusammenfassung

Miniaturization efforts and increasing demands regarding reliability of mechatronic systems require new materials and processes for the 3D mechatronic integrated devices (3D-MID) technology. Currently, in the area of 3D-MID mostly thermoplastic materials are in use in the industry, which are metallized using the LPKF-LDS® process. This paper is supposed to demonstrate the eligibility of thermoset resins as a new material class for 3D-MID applications and as a packaging option for silicon chips which are currently encapsulated using transfer molding of thermosets. The reliability of the conductor tracks made using a LDS-additive free process as well as the adhesion forces are investigated. Different laser parameters for structuring of two different substrate materials are compared. For reliability testing a thermal shock test is applied. Furthermore, the adhesion is tested using Hot-Pin-Pull testing. The conductor tracks surpass 2000 cycles thermo-mechanical load without showing strong deterioration of the track resistivity. The incorporated approach enables electrically reliable functionalization of packaged dummy chips including vias for connection to terminals on the chips. The results of the tested injection moldable thermoset resins are comparable to state-of-the-art 3D-MID thermoplastic substrates and thus, suited as circuit carrier material in electronic packaging.

Zusammenfassung

This work presents an embedding process for ultrathin silicon chips in mechanically flexible solder mask resist and their electrical contacting by inkjet printing. Photosensitive solder mask resist is applied by conformal spray coating onto epoxy bonded ultrathin chips with a daisy chain layout. The contact pads are opened by photolithography using UV direct light exposure. Circular and rectangular openings of 90 µm and 130 µm diameter, respectively, edge length are realized. Commercial inks containing nanoparticular silver and gold are inkjet printed to form conductive tracks between daisy chain structures. Different numbers of ink layers are applied. The track resistances are characterized by needle probing. Silver ink shows low resistances only for multiple layers and 90 µm openings, while gold ink exhibits low resistances in the single-digit Ω-range for minimum two printed layers.

Zusammenfassung

The trend of electrification and miniaturization brings the reliability of interconnects to the forefront. The solder joints are subjected to thermo-mechanical mismatch due to the Joule heating and electromigration (EM)-induced degradation under high current stressing conditions. However, most of the studies are limited to lab test samples or lab test conditions, which lack transferability in engineering applications. In this paper, automotive electronic components are studied subjected to field-like current pulse conditions. The work aims to understand the field-relevant failure modes of solder joints exposed to high current stressing via experimental and numerical investigations. Shunt components with and without Ni plating are analyzed in power cycling tests. A polarity effect is observed in the growth of intermetallic compounds (IMCs). The thickness of IMC at the anode exhibits an approximately linear growth with current stressing time, whereas the thickness of IMC at the cathode remains almost unchanged or slightly decreased. Ni, as diffusion barrier, serves to restrain Cu consumption from the terminals of shunts and also reduces Cu mass transport into and within the solder. The net Cu flux at the interface and in the solder is discussed to analyze the IMC growth kinetics. The shunts with Ni plating undergo less EM of Cu and yield longer lifetime. Voids and crack formation are detected in computer tomography (CT) scans and cross-sectional analysis by scanning electron microscopy (SEM). Finite element method (FEM) is implemented to simulate thermo-electro-mechanical fields of the assembly under power cycling test conditions. The distribution of divergence of material flux density corresponds well with the location of voids formation and provides good estimation for the lifetime.

Zusammenfassung

Molding techniques allow the replication of surface structures to enable improved or novel functions for optics, fluidics and further applications. In general, the molding process can be facilitated by means of antiadhesive-coated molds due to a reduction of demolding forces, wear or prevention of heat dissipation. Consequently, employing coated molds, an improved demolding of features with submicron dimensions and high aspect ratio can be expected. In order to achieve adequate results regarding the replication of nanostructures, accurate mastering techniques to structure the coating are required. One possible technique is focused ion beam (FIB) writing, which was investigated in this study regarding its suitability to mill structured surfaces of submicron dimensions into coated mold inserts. Mold inserts were coated with a thin-film diamond-like carbon (DLC) and chromium nitride (CrN) as well as electroless plated nickel-phosphorus (NiP). The coatings were examined by means of SEM imaging and roughness measurements regarding their applicability for the creation of nanostructures. Subsequently, a test pattern was written into the coatings using a FIB-SEM dual beam system. The test pattern consisted of the USAF test chart target groups 9, 10 and a Siemens star. The lateral dimensions were ≤ 980 nm. During ion beam milling, the beam parameters current and the number of scan repetitions were varied to investigate their influence on the structuring result. Subsequently, SEM measurements were conducted to characterize the milled nanostructures. Different lateral resolutions and depths of the pattern and effects like redeposition or the proximity effect were observed for the nanostructures depending on the coating and processing conditions. Lateral feature sizes down to 60 nm could be realized. In conclusion, the gained results approved FIB writing as a suitable technique to manufacture highly precise nanostructures into surface coatings for molding.

Zusammenfassung

Flexible electronics is a rapidly growing technology for a multitude of applications. Wearables and flexible displays are some application examples. Various technologies and processes are used to produce flexible electronics. An important aspect to be considered when developing these systems is their reliability, especially with regard to repeated bending. In this paper, the frequently used methods for investigating the bending reliability of flexible electronics are presented. This is done to provide an overview of the types of tests that can be performed to investigate the bending reliability. Furthermore, it is shown which devices are developed and optimized to gain more knowledge about the behavior of flexible systems under bending. Both static and dynamic bending test methods are presented.

Zusammenfassung

System-in-foil technology continues to realize relevance in industry and research. In this article, a digital process chain for the fabrication of bend-sensitive sensor structures on a flexible polyimide foil is described. This means that none of the steps in this process chain requires the manufacturing of a structured mask or cliché. Therefore, an arbitrary layout can be manufactured and easily be changed without major effort. Patterning of the sensor layout is realized by direct imaging of a laminated dry film photoresist. The sensor structure is fabricated by a liftoff process using sputtering of a NiCr layer. Finally, the sensor structures are characterized by a static bending test.

Zusammenfassung

Die Herstellung von dreidimensionalen Schaltungsträgern aus spritzgegossenen Thermoplasten, welche mittels Laserdirektstrukturierung und anschließender außenstromloser selektiver Metallisierung funktionalisiert werden, ist mittlerweile Stand der Technik. Bei erhöhter thermischer und/oder mechanischer Belastung z.B. durch Steigerung der elektrischen Leistungsdichte, stoßen Thermoplaste jedoch an ihre Grenzen. Hier bieten keramische Substratmaterialien klare Vorteile. Die Herstellung von solchen keramischen Schaltungsträgern mittels laserinduzierter Direktmetallisierung wurde erfolgreich realisiert. Hierfür wurden zwei Unterschiedliche Varianten an Al2O3-Keramiken untersucht. In der ersten Variante erfolgte das Sintern der Al2O3-Keramiken in H2-Atmosphäre, in Variante 2 wurden die Al2O3-Keramiken mit Cr2O3 dotiert und an Luft gesintert. Anschließend erfolgte für beide Varianten eine Laserstrukturierung mit darauffolgender außenstromloser Metallisierung. Somit ließen sich 3D-Schaltungsträger mit hoher thermischer Belastbarkeit, einer geringen Wärmeausdehnung und einer guten elektrischen Isolation herstellen. Die abgeschiedenen Metallschichten zeigten vergleichbare und zum Teil bessere Eigenschaften als solche auf klassischen thermoplastischen 3D-Schaltungsträgern. Three-dimensional interconnect devices based on injection molded thermoplastics, which are laser direct structured and subsequently plated via selective electroless metallization are meanwhile the state-of-the-art. With increased thermal and or mechanical load, e.g. at high electric power densities, ceramic materials show superior properties compared to thermoplastic materials. The fabrication of ceramic interconnect devices based on laser-induced metallization has been successfully demonstrated. Therefore, Al2O3 has been used, which was either sintered in H2-atmosphere or doped with Cr2O3 and sintered in air, followed by laser structuring and electroless metallization. Thereby, 3D interconnect devices with high thermal robustness, low thermal expansion and good electric isolation could be manufactured. The metallization on ceramics showed similar or even better properties than on conventional thermoplastic substrates.

Zusammenfassung

In this study, a 3-D dispensing method for nonconductive and conductive adhesives is introduced that allows for direct electrical functionalization of the printed part during the printing process. The experimental work's focus lies on the analysis of the embedding of conductive tracks within nonconductive housings. Two different construction strategies have been analyzed for printing tracks in both xy- and z-directions. For all variants, initial feasibility tests were performed that successfully validated the general applicability of these techniques. As dissimilar materials are involved in the process, a micrograph analysis was used to investigate possible negative effects within the transitional areas. Although prototypical parts can be built easily with additive manufacturing methods, the lack of knowledge about the long-term robustness is often the limiting factor to end-use applications. Accelerated life tests in the form of thermal shock and humidity testing were performed to investigate this issue. The tests demonstrate good long-term behavior for two of four adhesives. The obtained results show that the proposed method and process variants are capable of producing electronically functional parts, provided a careful material selection has been performed. Furthermore, several design rules concerning the transitional area could be derived

Zusammenfassung

Essential quality features of pressure sensors are, among other accuracy-related factors, measurement range, operating temperature, and long-term stability. In this work, these features are optimized for a capacitive pressure sensor with a measurement range of 10 bars. The sensor consists of a metal membrane, which is connected to a PCB and a digital capacitive readout. To optimize the performance, different methods for the joining process are studied. Transient liquid phase bonding (TLP bonding), reactive joining, silver sintering, and electric resistance welding are compared by measurements of the characteristic curves and long-term measurements at maximum pressure. A scanning electron microscope (SEM) with energy-dispersive X-ray spectroscopy (EDX) analysis was used to examine the quality of the joints. The evaluation of the characteristic curves shows the smallest measurement errors for TLP bonding and sintering. For welding and sintering, no statistically significant long-term drift was measured. In terms of equipment costs, reactive joining and sintering are most favorable. With low material costs and short process times, electric resistance welding offers ideal conditions for mass production.

Zusammenfassung

In this paper, a fluidic capacitive inclination sensor is presented and compared to three types of silicon-based microelectromechanical system (MEMS) accelerometers. MEMS accelerometers are commonly used for tilt measurement. They can only be manufactured by large companies with clean-room technology due to the high requirements during assembly. In contrast, the fluidic sensor can be produced by small- and medium-sized enterprises (SMEs) as well, since only surface mount technologies (SMT) are required. Three different variants of the fluidic sensor were investigated. Two variants using stacked printed circuit boards (PCBs) and one variant with 3D-molded interconnect devices (MIDs) to form the sensor element are presented. Allan deviation, non-repeatability, hysteresis, and offset temperature stability were measured to compare the sensors. Within the fluidic sensors, the PCB variant with two sensor cavities performed best regarding all the measurement results except non-repeatability. Regarding bias stability, white noise, which was determined from the Allan deviation, and hysteresis, the fluidic sensors outperformed the MEMS-based sensors. The accelerometer Analog Devices ADXL355 offers slightly better results regarding offset temperature stability and non-repeatability. The MEMS sensors Bosch BMA280 and TDK InvenSense MPU6500 do not match the performance of fluidic sensors in any category. Their advantages are the favorable price and the smaller package. From the investigations, it can be concluded that the fluidic sensor is competitive in the targeted price range, especially for applications with extended requirements regarding bias stability, noise, and hysteresis.

Zusammenfassung

In this paper, we introduce an improved, three-dimensional coplanar line structure manufactured using Laser Direct Structuring (LDS) technology. The low-loss and robust against tolerance transmission line structure can be used for building conformal millimeter wave (mmWave) sensor applications as e.g. automotive radar.

Zusammenfassung

Drehwinkelsensoren werden in zahlreichen Anwendungen u.a. zur Positionserfassung benötigt. Ein neuer Ansatz ermöglicht hoch miniaturisierte optische Drehwinkelsensoren in der neben dem Drehwinkel auch zusätzliche Sensorik sowie ein frei programmierbarer Mikrocontroller integriert sind. Dadurch können direkt im Sensor Abgleich- und Diagnosefunktionen implementiert und Zusatzinformationen wie Drehzahl und Beschleunigungen abgeleitet werden. Ferner erfasst und verarbeitet der Mikrocontroller die Messwerte, wie Gehäuse- und Wellenvibrationen und die Umgebungstemperatur. Dadurch lässt sich mit Hilfe von Kompensationsalgorithmen auf den Betriebszustand des Sensors schließen. Der Drehwinkelsensor soll eine Auflösung von 15 Bit bei einem Bauraum von nur rund einem Kubikzentimeter erreichen.

Zusammenfassung

Since the last five decades, polymer-derived ceramics (PDCs) are in use and envisaged for a variety of applications. The transition of a precursor to an inorganic ceramic by pyrolysis and heat-treatment results in either amorphous or nanocrystalline composites with the evolution of phases strongly controlled by the processing conditions. Understanding the deformation behaviour under ambient conditions and at elevated temperatures is key to designing these materials for long-term use. However, quantitative reliable estimation of mechanical properties is quite challenging due to its unique structure which in turn is strongly governed by the precursor chemistry. The mechanical behaviour of PDCs in the form of fibres, bulk and foams are different and they are discussed separately. Both experimental and simulation-based studies are considered in this review. Recently, additive manufacturing processes have been used for the fabrication of PDCs, the mechanical properties of which are also included in this review.

Zusammenfassung

Inkjet-printing of nanoparticle inks allows the integration of electrodes directly into 2.5D structures, like microfluidic chambers. Sensing applications can additionally benefit from the nanoporous morphology of the printed electrodes. The presented results demonstrate that the high effective surface of the porous electrode is suitable for functionalization by immobilizing DNA and determining the DNA density. It is envisioned that the method facilitates the integration of porous electrodes into microfluidic systems.

Zusammenfassung

Bladder tumor recurrence is a serious problem in uro-oncology, as it increases the risk of fatal progression and makes further surgeries necessary. The possibility of intraoperative tissue differentiation can help for diagnostic purposes as well as for ensuring that the entirety of the tumor is removed. The latter not only differ visually from healthy tissue, but also in their mechanical and electrical properties due to an altered physiology. A possible base for intraoperative tissue differentiation are impedance measurements, which are, however, difficult to obtain passing through the limited space of the urethra. This work presents a comparative study of two impedance sensors, which are obtained by laser direct structuring and rely on a four terminal measurement. The miniaturized sensors are suitable for minimally invasive usage. Circular electrodes are placed in a square for a first sensor, whereas a novel combination of one circular electrode and three concentric rings is designed for the second sensor. For each sensor, the specific geometry factor is determined and the impact of sensitivity towards small conductivity changes inside the tissue investigated. Furthermore, multiple ex vivo measurements on fresh pig bladders are carried out with each sensor. It is shown that both sensors reliably determine tissue impedance data that fit empirical tissue models. Conductivity values close to listed data of human urinary bladder are obtained. Ultimately, the novel ring sensor configuration turns out more favorable in terms of sensitivity distribution and yields more reproducible results than the square electrode arrangement.

Zusammenfassung

The production of injection-molding prototypes, e.g., molded interconnect devices (MID) prototypes, can be costly and time-consuming due to the process-specific inability to replace durable steel tooling with quicker fabricated aluminum tooling. Instead, additively manufactured soft tooling is a solution for the production of small quantities and prototypes, but producing complex parts with, e.g., undercuts, is avoided due to the necessity of additional soft tooling components. The integration of automated soft slides into soft tooling has not yet been investigated and poses a challenge for the design and endurance of the tooling. The presented study covers the design and injection-molding trial of soft tooling with integrated automated slides for the production of a complex MID prototype. The design further addresses issues like the alignment of the mold components and the sealing of the complex parting plane. The soft tooling was additively manufactured via digital light processing from a silica-filled photopolymer, and 10 proper parts were injection-molded from a laser-direct structurable glass fiber-filled PET+PBT material before the first damage on the tooling occurred. Although improvements are suggested to enhance the soft tooling durability, the designed features worked as intended and are generally transferable to other part geometries.

Zusammenfassung

In order to economize injection molded prototypes, additive manufacturing of, e.g., curable plastics based tools, can be employed, which is known as soft tooling. However, one disadvantage of such tools is that the variothermal process, which is needed to produce polymeric parts with small features, can lead to a shorter lifespan of the tooling due to its thermally impaired material properties. Here, a novel concept is proposed, which allows to locally heat the mold cavity via induction to circumvent the thermal impairment of the tooling material. The developed fabrication process consists of additive manufacturing of the tooling, PVD coating the mold cavity with an adhesion promoting layer and a seed layer, electroplating of a ferromagnetic metal layer, and finally patterning the metal layer via laser ablation to enhance the quality and efficiency of the energy transfer as well as the longevity by geometric measures. This process chain is investigated on 2D test specimens to find suitable fabrication parameters, backed by adhesion tests as well as environmental and induction tests. The results of these investigations serve as proof of concept and form the base for the investigation of such induction layers in actual soft tooling cavities.

Zusammenfassung

In this paper, the usability of the classical Harmonic Balancing method (cHB) to calculate the weakly nonlinear motion of phase- and amplitude controlled MEMS resonators is demonstrated. A polynomial mechanical stiffness description and linearized electrostatic effects are considered, which allow determining the Jacobian analytically. The effects of amplitude and phase control are taken into account by applying boundary conditions in the iteration process. With a customized cHB, it is possible to efficiently simulate the behavior of a MEMS gyroscope undergoing nonlinear resonance with higher parasitic modes. The presented results of a virtual model compare very well with solutions obtained with the Shooting method. Furthermore, we compare the measurement of a drive frequency discontinuity, taken from a different prototype, with the prediction from our linear extrapolated model and from a model with artificially fitted parameters. The cHB approach yields an order of magnitude speed-up in comparison to the transient simulation method. Besides some restrictions, customized cHB methods are interesting candidates for fast system-type simulation considering the MEMS-ASIC interface. 2021-0028

Zusammenfassung

Some of the most important quality assets of Laser Direct Structured Molded Interconnect Devices (LDS-MID) are their efficiency and reliability. In order to identify the production parameters and materials, which yield devices with superior performance, the following studies were conducted. Initially, a Design of Experiments (DoE) allowed making a qualitative and quantitative statement about conductor track defects and their causes as well as about the efficiency due to the electrical conductivity of the tracks. These results were used to suggest certain combinations of substrate material and metal layer to improve the production quality of MIDs. Such findings guide the path towards high-performance LDS-MIDs, which can be operated under harsh conditions. Along this line, specimens of 16 different factor-combinations were subjected to a temperature shock test, whereby the resistance value of the conductor tracks could be continuously measured, using a four-wire measurement. The latter allowed a precise detection of conductor cracks or solder joint failures. It appeared that most of the chosen factorcombinations showed an almost constant electrical resistance during the temperature shock tests. However, the type of thermoplastic substrate material, as well as the heat input by the soldering process, could be identified as the factors with the most significant influence on reliability and electrical conductivity.

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The project “key enabling technologies for clean production” (KET4CP), which is supported by the European Commission, has the aim to connect small and medium-sized enterprises (SME) and Technology Centres (TC) for cleaner, greener and more efficient production. Within this context, SMEs and TCs across Europe work together to establish an open-innovation network and to raise awareness in productivity and environmental performance. This article presents how an open European network of TCs opens its innovation process to support SMEs to become cleaner, greener and more efficient. Furthermore, this article shows how the TCs and SMEs become a part of the open-eco-innovation platform in clean production and how successful the open-eco-innovation process of different European countries is. We revealed that a pan-European open innovation process for eco-innovations with TCs for key enabling technologies (KET TCs) and Enterprise Europe Network partners (EEN) is a successful approach for SMEs that want to produce and develop cleaner products. An application example is mentioned, in which TCs from different European countries have contributed to developing a product of a SME for energy harvesting. The SME, together with the TCs, developed a generator that is installed in city-level water supply pipes and so, it is outstanding in its application. This innovative application is also described in this article.

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The design for the reliability of automotive electronics involving viscoelastic materials requires accurate knowledge of material properties under critical frequency and temperature conditions. Both forward and inverse approaches for the dynamic characterization of a soft silicone-based thermal interface material used in electronic control units are presented and discussed. The classic forward characterization implying dynamic mechanical analysis and the principle of time-temperature superposition is applied in a first step. The identified material model under critical temperature conditions is restrained to a narrow frequency range and a validation for higher frequencies is needed. The proposed inverse method presented in the second part minimizes the residue between the measured and numerical transfer functions of single-lap joint specimens at chosen control frequency ranges located at the resonances of the structure. The specimens are excited by an electrodynamic shaker situated in an environmental chamber allowing measurements under different temperature conditions. The main outcome of the inverse approach is a validation of the results of forward characterization for a broad frequency range and under critical temperature conditions adopting a simple experimental arrangement and a barely complex numerical procedure.

Zusammenfassung

Reconfigurable manufacturing systems (RMS) can be used to produce micro-assembled products that are too complex for assembly on flat substrates like printed circuit boards. The greatest advantage of RMS is their capability to reuse machine parts for different products, which enhances the economical efficiency of quickly changing or highly individualized products. However, often, process engineers struggle to achieve the full potential of RMS due to product designs not being suited for their given system. Guaranteeing a better fit cannot be done by static guidelines because the higher degree of freedom would make them too complex. Therefore, a new method for generating dynamic guidelines is proposed. The method consists of a model, with which designers can create a simplified assembly sequence of their product idea, and another model, with which process engineers can describe the RMS and the procedures and operations that it can offer. By combining both, a list of possible machine configurations for an RMS can be generated as an automated response for a modeled assembly sequence. With the planning tool for micro-assembly, an implementation of this method as a modern web application is shown, which uses a real existent RMS for micro-assembly.

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Thermoset materials offer a multitude of advantageous properties in terms of shrinkage and warpage as well as mechanical, thermal and chemical stability compared to thermoplastic materials. Thanks to these properties, thermosets are commonly used to encapsulate electronic components on a 2nd-level packaging prior to assembly by reflow soldering on printed circuits boards or other substrates. Based on the characteristics of thermosets to develop a distinct skin effect due to segregation during the molding process, the surface properties of injection molded thermoset components resemble optical characteristics. Within this study, molding parameters for thermoset components are analyzed in order to optimize the surface quality of injection molded thermoset components. Perspectively, in combination with a reflective coating by e.g., physical vapor deposition, such elements with micro-integrated reflective optical features can be used as optoelectronic components, which can be processed at medium-ranged temperatures up to 230 °C. The obtained results indicate the general feasibility since Ra values of 60 nm and below can be achieved. The main influencing parameters on surface quality were identified as the composition of filler materials and tool temperature.

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Hermeticity of an electronic package defines its effectiveness to seal and protect the encapsulated electronics from the ingress of contaminants, gases, and moisture, as well as helping avoid toxic materials from inside the capsule contacting tissue. Using accelerated testing by methods of leak detection analysis, the theoretical limit of the lifetime due to water ingress of an encapsulated device can be estimated. However, classical methods are not sufficient for microencapsulations and exhibit limitations due to the resolution of the detection mechanisms required for such small cavities. With the availability of cumulative helium leak detection (CHLD), the detection limits can be extended by several magnitudes of resolution. However, limitations due to the physics of leakage apply. This article discusses the limitations concerning the ability for combined gross and fine leak testing in combination with outgassing effects using CHLD for miniaturized implantable medical devices. Practical aspects are evaluated regarding the applicability of CHLD for such microencapsulations at the example of an AuSn-sealed alumina package.

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Increasing demands regarding reliability of mechatronic systems and the aim for miniaturization require new materials and processes for the 3D mechatronic interconnect devices (3DMID) technology to fulfill those demands. For the first time, this paper demonstrates the solderability of a new material class for 3D-MID applications, down to the SMD component size 01005. Instead of standard and state-of-the-art thermoplastic materials such as polyamide or high-performance thermoplastic materials commercial injection moldable thermoset resins were used. They were selectively metallized by laser structuring and electroless plating. Different laser parameters for structuring of two different substrate materials were investigated. SMD resistor components with the size 0805, 0402, 0201 and 01005 were used to evaluate material solderability on stencil printed solder pads. Specimen were analyzed using optical analysis, metallographic examination and shear tests. The results show that component size and laser energy have the most significant effect on shear strength and defects. Eligibility for common soldering processes in electronics packaging was proven. Additionally, soldering results between convection soldering and vapor phase soldering were compared, showing higher shear forces for samples soldered in the convection oven. Based on the results the tested injection moldable thermoset resins are suited as circuit carrier material in electronic packaging.

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This paper presents a feasibility study of an automated pick-and-place process for ultrathin chips on a standard automatic assembly machine. So far, scientific research about automated assembly of ultrathin chips, with thicknesses less than 50 µm, is missing, but is necessary for cost-effective, high-quantity production of system-in-foil for applications in narrow spaces or flexible smart health systems applied in biomedical applications. Novel pick-and-place tools for ultrathin chip handling were fabricated and a process for chip detachment from thermal release foil was developed. On this basis, an adhesive bonding process for ultrathin chips with 30 µm thickness was developed and transferred to an automatic assembly machine. Multiple ultrathin chips aligned to each other were automatically placed and transferred onto glass and polyimide foil with a relative placement accuracy of ±25 µm.

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Digital printing technologies, such as inkjet or aerosol jet, are becoming increasingly interesting for the manufacturing of electronic devices. As a maskless and contactless process, it offers the potential for low-cost deposition of functional materials onto flat, flexible, or 3-D substrates. Common inks used for printed electronics are nanoparticle (NP) metal inks. Silver (Ag) is widely used because of its excellent conductivity, but also gold (Au) inks are of interest for several applications. By using NP inks, it is possible to integrate conductive paths and sensors onto temperature-sensitive substrate materials, such as polymers. Polymers often need a pretreatment, such as a plasma treatment for improving the wetting. Plasma treatment usually changes the wetting behavior of the complete substrate surface. This could be critical for some applications, e.g., fluidic applications, where the original properties of the substrate should be kept. Low-pressure plasma as a vacuum process is also difficult for implementation into an existing process. In this article, laser irradiation for local improvement in wetting of an inkjet-printed gold ink on polymer substrates is investigated. The experiments show that laser irradiation is a very promising technique for the modification of polymer surfaces and suitable for inkjet printing NP inks on hydrophobic polymer surfaces. This offers new opportunities for printed electronics, which could be easily integrated into the existing processes.

Zusammenfassung

Mechatronic Integrated Devices (MID) made of thermoplastics (injection-molded circuit carriers) are now state of the art when it comes to applying electronic circuits and sensor technology to components with a complex 3D geometry. The technology has now also been successfully extended to ceramic 3D circuit carriers, which are characterized by improved chemical and thermal resistance and increased thermal conductivity, thus opening up additional fields of application.

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The measurement of the radio frequency reflection coefficient is widely used in characterizing various materials nondestructively. Generally, the measurement is done using a one port vector network analyzer together with some sort of probe. Here, the design theory of a new, low-cost replacement for such a network analyzer is explained. The proposed Cartesian reflection coefficient measurement block is outlined as well as the results of computer simulations and measurements on a printed circuit board (PCB) setup. Unlike previous approaches, it explores the use of injection locking to enhance the performance of quadrature amplitude demodulation of both the forward and the reflected waves as sampled from the output path of an ultrahigh-frequency power amplifier by a bidirectional coupler. Computer simulations at 400 MHz resulted in an average error of 3.4% full scale on the reflection coefficient, including extreme impedance values as well as various parasitic effects of the circuit measurements on a simplified PCB setup, also at 400 MHz.

Zusammenfassung

To date, several photonic applications have been demonstrated without considerable thermal management efforts. However, in phase-sensitive photonic applications, thermal management becomes of utmost importance. Thermal management of photonic systems requires not only efficient heat dissipation, but also reduction of on-chip temperature gradients. Particularly in highly integrated systems, in which several components are integrated within a single photonic integrated circuit, the reduction of on-chip temperature gradients is necessary to guarantee the correct functionality of the system. Due to their high integration density as well as their extreme temperature sensitivity, optical phased arrays are ideal examples of a system, where thermal management is required. Ideally, thermal management solutions of such systems should not require additional power for operation. Therefore, it is desired to improve the heat dissipation and to reduce temperature gradients by structural modifications of the photonic circuit. Furthermore, to cope with the advantages of silicon photonics, thermal management solutions must be compatible with series fabrication processes. In this work, complementary metal–oxide–semiconductor (CMOS)-compatible measures for thermal management of silicon photonic integrated circuits are proposed and validated by characterization of in-house fabricated thermal demonstrators. The proposed concepts are extremely efficient not only in reducing temperature gradients, but also in improving the heat dissipation from integrated heat sources.

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A fibre orientation dependent material model of the thermoset is implemented to predict the lifetime of electronic components as a part of 2nd level encapsulated packages. Experimental data are used in combination with coupled simulations (process simulation – fibre orientation dependant material model – thermo-mechanical simulation) for defining this lifetime prediction model. An already existing lifetime prediction model based on the Coffin-Manson relation is used initially to evaluate the prediction accuracy. The prediction model is then adjusted and fitted for the current application.

Zusammenfassung

A drastically growing requirement of electronic packages with an increasing level of complexity poses newer challenges for the competitive manufacturing industry. Coupled with harsher operating conditions, these challenges affirm the need for encapsulated board-level (2nd level) packages. To reduce thermo-mechanical loads induced on the electronic components during operating cycles, a conformal type of encapsulation is gaining preference over conventional glob-tops or resin casting types. The availability of technology, the ease of automation, and the uncomplicated storage of raw material intensifies the implementation of thermoset injection molding for the encapsulation process of board-level packages. Reliability case studies of such encapsulated electronic components as a part of board-level packages become, thereupon, necessary. This paper presents the reliability study of exemplary electronic components, surface-mounted on printed circuit boards (PCBs), encapsulated by the means of thermoset injection molding, and subjected to cyclic thermal loading. The characteristic lifetime of the electronic components is statistically calculated after assessing the probability plots and presented consequently. A few points of conclusion are summarized, and the future scope is discussed at the end.

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We investigate the influence of parametric excitations on MEMS vibration energy harvesters for energy autonomous sensor systems. In Industry 4.0 (or Industrial IoT) applications, interconnected sensors provide a means of data acquisition for automated control of the manufacturing process. Ensuring a continuous energy supply to the sensors is essential for their reliable operation. Manufacturing machines usually display a wide spectrum of vibration frequencies which needs to be covered by an array of harvester substructures in order to maintain the desired output level. We show that mechanical structures designed to implement a Helmholtz-Duffing oscillator have an increased bandwidth by exploiting several orders of parametric resonances. In contrast to concepts implementing parametric amplification in a multi-mode scenario, our concept is based on a single mechanical mode. Therefore, it is more robust against fabrication tolerances as the relevant multi-mode resonance conditions do not need to be matched on the level of single chips. Using exact transient simulations and semi-analytic models to showcase the relation of the Helmholtz-Duffing oscillator to the damped and driven Mathieu equation, we show that parametric resonances highly increase the bandwidth of the output power whenever high Helmholtz nonlinearities are present. To achieve the required nonlinearities, we suggest nonlinear stress-strain curves and we propose to achieve such nonlinearities through field-induced striction by magneto- or electrostriction. In contrast to existing approaches, where external fields are harvested using strictive effects, we employ external fields that manipulate the effective Young’s modulus to achieve parametric excitations in a mechanical oscillator. Thus, we are able to propose a novel energy harvester concept incorporating strictive materials that exploits the effects of parametric excitations to achieve broadband vibrational energy harvesting.

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In this study slip cast alumina-zirconia materials were doped with nickel oxide and chromium oxide and sintered in air. Chromium oxide forms a solid solution while nickel oxide forms spinel with alumina. The sintered substrates were selectively irradiated with a green, ps pulsed Nd:YVO4 laser. During subsequent autocatalytic plating, copper was deposited selectively on laser-irradiated surfaces. It is assumed that under the irradiation influence at very high temperatures metal or lower valence oxides are produced which initiate the growth of copper crystallites during the plating process. The process offers the opportunity to manufacture 3D integrated circuit carriers with ceramic substrates, which offer superior strength, thermal stability and heat conductivity compared to polymers. Single dopant or co-dopant contents of < 2 wt% are sufficient to induce a reliable laser activation at a broad range of laser parameters which enables the application of very narrow continuous conductor paths.

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We demonstrate mass production compatible fabrication of polymer-based micro Fresnel lenses by injection compression molding. The extremely robust titanium-molding tool is structured with high precision by focused ion beam milling. In order to achieve optimal shape accuracy in the titanium we use an iterative design optimization. The inverse Fresnel lens structured into the titanium is transferred to polymers by injection compression molding, enabling rapid mass replication. We show that the optical performance of the molded diffractive Fresnel lenses is in good agreement with simulations, rendering our approach suitable for applications that require compact and high-quality optical elements in large numbers.

Zusammenfassung

The use of 3D printing technologies enhanced with component placement and electrical interconnect deposition enables electronic systems with freedom in fabrication and complex embedded circuitry. However, with more electrical functionality being integrated, new material requirements become increasingly important. Well-established adhesive systems in electronic packaging have the potential to fulfill these requirements. This paper introduces a novel approach for processing adhesives with an extrusion-based UV-assisted 3D dispensing process. A specimen study revealed promising results for three out of six adhesives (denoted as A, D, E), for which an extensive anisotropy evaluation was performed: The relationship between the layered construction strategy and the material properties of the printed parts was characterized by micrograph analysis, tensile testing along with fracture analysis and laser flash analysis. An exemplary study for one adhesive via tensile testing showed no significant difference between three printing orientations. However, different construction strategies influenced the degree of anisotropy. The epoxy/acrylate (A) and polycarbamin system (D) showed higher strength and strain values when printed horizontally, indicating that the adhesive strength between the layers was not sufficient. The interlayer bonding for the epoxy system (E) was better due to the crosslinking between the layers. In addition, the evaluation of thermal anisotropy revealed a link between the thermal conductivity and the rate of the UV-curing for A and D. For material E, no significant difference was measured. The work presented in this article shows that dual-curing adhesives, in particular epoxy systems, are promising choices for additive manufacturing: It was possible to print fine geometries with good material properties and low anisotropy. These results are appealing since a wide variety of different adhesive systems is available. The findings serve to derive first design rules and provide a basis for further studies.

Zusammenfassung

Inkjet technology as a maskless, direct-writing technology offers the potential for structured deposition of functional materials for the realization of electrodes for, e.g., sensing applications. In this work, electrodes were realized by inkjet-printing of commercial nanoparticle gold ink on planar substrates and, for the first time, onto the 2.5D surfaces of a 0.5 mm-deep microfluidic chamber produced in cyclic olefin copolymer (COC). The challenges of a poor wetting behavior and a low process temperature of the COC used were solved by a pretreatment with oxygen plasma and the combination of thermal (130 &deg;C for 1 h) and photonic (955 mJ/cm&sup2;) steps for sintering. By performing the photonic curing, the resistance could be reduced by about 50% to 22.7 &micro;Ω cm. The printed gold structures were mechanically stable (optimal cross-cut value) and porous (roughness factors between 8.6 and 24.4 for 3 and 9 inkjet-printed layers, respectively). Thiolated DNA probes were immobilized throughout the porous structure without the necessity of a surface activation step. Hybridization of labeled DNA probes resulted in specific signals comparable to signals on commercial screen-printed electrodes and could be reproduced after regeneration. The process described may facilitate the integration of electrodes in 2.5D lab-on-a-chip systems.

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Traceability of single parts is essential in automated manufacturing, especially considering recent developments in Industry 4.0 or Smart Manufacturing. In some cases, however, conventional traceability methods, e.g. barcode, DMC or RFID, are not sufficient to track individual components through their entire production chain. One solution is the exploitation of an object’s inherent, individual surface patterns. This work demonstrates label-/tag-free traceability of approx. 1000 components in a molded interconnect device (MID) production chain. The parts’ surface patterns are photographed several times along the MID production chain. Based on the captured images nearly 3300 successful identification processes were performed without any failure. Using a hash algorithm to compress the relevant data of the surface pattern images reduces the required disk space and the runtime significantly. Since the results demonstrate the robustness against surface alterations, this work gives the proof of concept regarding to a method for fast label-/tag-free part tracking that is applicable in an industrial production line.

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Silicon photonic optical phased arrays leveraging from the well established CMOS fabrication process have become promising candidates to realize miniaturized beam steering systems. While different implementations of optical phased arrays have been successfully demonstrated, no investigations on the influence of thermal distortions on the response of these systems have been performed so far. Due to the high thermo-optic coefficient of silicon, the refractive index and thus the functionality of silicon photonic components depend strongly on the temperature. In highly integrated systems, consisting of several photonic components, in which laser sources and control electronics are directly integrated on top of the photonic IC, heat dissipated by active components leads to temperature gradients and offsets, affecting the functionality of the photonic system. Optical phased arrays consisting of an array of phase sensitive components, are particularly sensitive towards temperature. Therefore, precise investigations of the temperature dependence of the OPA functionality are required. This article aims to expand the understanding of the influence of thermal distortions on the steering angles of optical phased arrays. Thereto, analytical expressions describing the temperature dependence of the steering angles are provided and experimentally validated. The expressions are provided in a general form so that they can be applied to any OPA system regardless of its implementation.

Zusammenfassung

A newly developed laser-assisted process is presented, by which a selective additive metallization of injection-molded alumina ceramic substrates without additional additives is enabled. Alumina substrates were manufactured by ceramic injection molding (CIM) with subsequent debinding and sintering. The substrate surfaces are activated by laser patterning for subsequent electroless plating of the activated areas with copper, nickel, and gold. Three-dimensionally shaped ceramic interconnect devices are enabled by CIM combined with 3-D laser patterning. The conducting paths fabricated in this way are characterized and compared to conducting paths made by a laser-direct-structure technology on thermoplastics developed by the company LPKF Laser & Electronics AG (LPKF-laser direct structuring process). The obtained metal layer thickness with about 10 μm is similar to metal layer thickness on thermoplastic substrates. Obtained metal surface roughness on ceramic substrates of below 10 μm is even lower than on thermoplastics. The high adhesion of approximately 30 N mm −2 combined with the low thermal expansion coefficient of the alumina substrate promises good reliability even under thermal load.

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Faster product lifecycles make long-term investments in machines for micro assembly riskier. Therefore, reconfigurable manufacturing systems gain more and more attention. But most companies are uncertain if a reconfigurable manufacturing system can fulfill their needs and justify the initial investment. New and improved techniques for product development have the potential to foster the utilization and decrease the investment risk for such systems. In this paper, four different methods for product development are reviewed. A set of criteria regarding micro assembly on reconfigurable manufacturing systems RMS is established. Based on those criteria and the assessment, a novel approach for a product development method is provided, which tries to combine the strengths of the beforehand presented approaches. It focuses on the conceptual design phase to overcome the customers&rsquo; uncertainty in the development process. For this, an abstract representation of a micro-assembly product idea as well as a decision tree for joining processes are established and validated by real product ideas using expert interviews. The validation shows that the conceptual design phase can be used as a useful tool in the product development process in the field of micro assembly.

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This article presents a simple approach for high-accuracy assembly of multiple ultrathin chips on flexible foil substrates. The chips are placed initially in the cavities on a chip carrier substrate and transferred onto a thermally releasable adhesive tape. After application of the epoxy-based adhesive onto the chip surface, the chips are transferred onto the foil substrate. Finally, the epoxy adhesive is cured and the adhesive tape is removed. It was found that a wafer dicing tape with a releasing temperature of 90 °C as thermally releasable adhesive tape and a two-component epoxy adhesive with a curing temperature of 65 °C is suitable for the process. High placement accuracy of the chips of less than 30 μm in the x- and y-orientation as well as rotational misalignment lower than 0.2° were obtained. The process is demonstrated on a polyimide foil with a resulting chip flatness of ±5 μ

Zusammenfassung

Digital printing technologies are well suited for structured deposition of functional materials such as nanoparticular metal inks on different substrates. Inkjet printing as a maskless and direct writing technology is very suitable for the manufacturing of low-cost devices and packages, e.g., for highly integrated sensor systems. The availability of printable materials is ever expanding and enables new capabilities in many applications. Currently, nanoparticular silver inks are very popular for inkjet printing of conductive paths. However, at present, the availability of reliable technologies for the assembly of electrical components is a challenge. In this paper, the soldering of chip resistors on inkjet-printed silver structures was investigated.

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Radio frequency reflectometry is widely used in non-destructive characterization of various materials and can also be applied to automatic impedance matching systems in telecommunication devices. Here, a novel, low cost, software defined approach for measuring the reflection coefficient without using mixers or power detectors is proposed, enabled by using under-sampling down-conversion with an analog-digital-converter. Minimizing the analog part of the system removes possible error sources and a modular design allows application in different fields as well as an implementation as an integrated circuit. Computer simulations as well as measurement results on a printed circuit board setup for a system frequency of 400 MHz are presented, permitting extrapolation to other ultra-high frequencies.

Zusammenfassung

An ever-growing market demand for board (second) level packages (e.g., embedded systems, system-on-a-chip, etc.) poses newer challenges for its manufacturing industry in terms of competitive pricing, higher reliability, and overall dimensions. Such packages are encapsulated for various reasons including thermal management, protection from environmental conditions and dust particles, and enhancing the mechanical stability. In the due course of reducing overall sizes and material saving, an encapsulation as thin as possible imposes its own significance. Such a thin-walled conformal encapsulation serves as an added advantage by reducing the thermo-mechanical stresses occurring due to thermal-cyclic loading, compared to block-sized or thicker encapsulations. This paper assesses the encapsulation process of a board-level package by means of thermoset injection molding. Various aspects reviewed in this paper include the conception of a demonstrator, investigation of the flow simulation of the injection molding process, execution of molding trials with different encapsulation thicknesses, and characterization of the packages. The process shows a high dependence on the substrate properties, injection molding process parameters, device mounting tolerances, and device geometry tolerances. Nevertheless, the thermoset injection molding process is suitable for the encapsulation of board-level packages limiting itself only with respect to the thickness of the encapsulation material, which depends on other external aforementioned factors.

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Research based as well as industrialized harvester developments indicate that electrodynamic energy harvesters (EHs) outperform piezoelectric EHs in macroscopic designs for narrow banded resonance-based transducers. This paper investigates how multiple vibration EHs can be combined to a macroscopic array configuration that covers 100–600 Hz by aiming not on high resonance peak powers but on close spectral overlapping in lower power regions of 0.5 mW. The 500 Hz-wide array is able to harvest vibrational energy from a multitude of machinery, independent of vibration frequency determining shaft speeds or flows. The novelty of this paper consists in the result that combining piezoelectric EHs to arrays outperforms electrodynamic arrays with respect to their volumetric power density for 500 Hz-wide operation. Further optimization is reached by introducing nonlinearities for the piezoelectric array. The presented design allows a flat integration of piezoelectric EH-arrays as power supply for energy autonomous sensor systems.

Zusammenfassung

Energy autonomous sensors for I4.0 applications powered by kinetic energy harvesters (KEHs) are widely discussed – especially in terms of vibration harvesting. Typically, industrial linear stages offer weak vibrations, so other inertia-based harvesting methods are investigated. This study investigates the usability of human motion energy harvesters in industrial linear motion technology for the first time. Two KEHs – harvesting swing or shocks, respectively – are tested while controlling the parameters velocity, acceleration, and jerk-limitation according to the real applications’ parameter ranges. The swing-KEH and the shock-KEH harvested up to 106 and 124 mW, respectively. Furthermore, a parameter study is performed assuming constant driving lengths with optimised stroke rates to obtain a generalised power and energy profile for each harvester. The analytically obtained overall average power is 22 mW for the swing-KEH and 14 mW for the shock-KEH. The analytical investigation revealed that a reciprocal dependency of performance and velocity exists for both KEHs, respectively. Both experimental and analytical parts show that the wireless sensor node for I4.0 on industrial linear stages can be powered by harvesters made for human motions.

Zusammenfassung

When electronic assemblies are experiencing high current loading conditions, thermo-mechanical mismatch induced from the local Joule heating of the component and electromigration (EM)-induced void formation can lead to the failure of the solder interconnect. Scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) are adopted to investigate the microstructural evolution of solder joints of shunt components subjected to current stressing. Voids and micro-cracks initiate at the corner of solder meniscus, where the maximal divergence of material flux density is located on the basis of finite element method (FEM) simulation. The EM-induced voids introduce higher accumulated plastic strain in the solder joints, which will result in reduction in the lifetime of the electronic assemblies.

Zusammenfassung

Electron spins in solids constitute formidable quantum sensors. Individual defect centers in diamond were used to detect individual nuclear spins with nanometer scale resolution, and ensemble magnetometers rival SQUID and vapor cell magnetometers when taking into account room temperature operation and size. NV center spins can also detect electric field vectors, despite their weak coupling to electric fields. Here, we employ ensembles of NV center spins to measure macroscopic ac electric vector fields with high precision. We utilize low strain, 12C enriched diamond to achieve maximum sensitivity and tailor the spin Hamiltonian via proper magnetic field adjustment to map out the ac electric field strength and polarization and arrive at refined electric field coupling constants. For high precision measurements we combine classical lock-in detection with aspects from quantum phase estimation for effective suppression of technical noise. Eventually, this enables t^-1/2 uncertainty scaling of the electric field strength over extended averaging periods, enabling us to measure electric fields down to 10^-7 V/μm for an AC electric field with a frequency of 2 kHz and an amplitude of 0.012 V/µm.

Zusammenfassung

The fabrication of microstructured polymer optics enables a multitude of new options in the design of technical optics. However, challenges arise along the varying process chains of mold insert fabrication, integration into molding tools, replication by means of injection compression molding and metrology. In order to study the effects, diffractive optical elements (DOE) and microlens arrays (MLA) are fabricated using two different process chains. DOEs are fabricated using a laser direct writing (LDW) based mold insert fabrication. The MLA mold insert is produced using ultra-precision milling (UP-milling). Both optical parts are replicated using injection compression molding. The occurring effects are discussed and the results show, that with complete process control high quality microstructured polymer optical parts can be produced and characterized.

Zusammenfassung

In this work, a new process chain for the fabrication of curved micro-structured optical elements by injection compression molding is investigated. The fabrication is demonstrated for the example of a curved diffractive optical element (DOE). In a first process step a master substrate is fabricated using laser direct writing on a curved glass substrate. Blazed diffractive micro-structures with lateral feature sizes down to 5 μm and height of 1.6 μm are created. A subsequent electroplating process is applied to create a nickel stamper to be used as a tool insert for the molding process. During electroplating, a 3 mm nickel layer is formed, transferring the diffractive structures from the master substrate into a solid mold insert. The nickel stamper shows an accurate reproduction of the micro-structures. The mold insert is integrated into an injection compression molding tool to replicate the optical elements. Results show that the blazed diffractive structures are replicated with a high quality. Tests of the components within a chromatic-confocal measurement setup confirm that they can potentially replace expensive conventional elements.

Zusammenfassung

Polymer optics have gained increasing importance in recent years. With advancing requirements for the optical components, the fabrication process remains a challenge. In particular, the fabrication of the mold inserts for the replication process is crucial for obtaining high-quality optical components. This review focuses on fabrication technologies for optical mold inserts. Thereby, two main types of technologies can be distinguished: fabrication methods to create mold inserts with optical surface quality and methods to create optical microstructures. Since optical mold inserts usually require outstanding form accuracies and surface qualities, a focus is placed on these factors. This review aims to give an overview of available methods as well as support the selection process when a fabrication technology is needed for a defined application. Furthermore, references are given to detailed descriptions of each technology if a deeper understanding of the processes is required.

Zusammenfassung

A novel optical incremental and absolute encoder based on an optical application-specific integrated circuit (opto-ASIC) and an encoder disc carrying micro manufactured structures is presented. The physical basis of the encoder is the diffraction of light using a reflective phase grating. The opto-ASIC contains a ring of photodiodes that represents the encryption of the encoder. It also includes the analog signal conditioning, the signal acquisition, and the control of a light source, as well as the digital position processing. The development and fabrication of the opto-ASIC is also described in this work. A laser diode was assembled in the center on top of the opto-ASIC, together with a micro manufactured polymer lens. The latter was fabricated using ultra-precision machining. The encoder disc was fabricated using micro injection molding and contains micro structures forming a blazed grating. This way, a 10-bit optical encoder with a form factor of only 1 cm3 was realized and tested successfully.

Zusammenfassung

Due to many advantages, such as cost-effective production, design freedom, and weight reduction, plastics have replaced metals and ceramics in many fields. However, engineering plastics are good thermal insulators. This characteristic, although beneficial in certain applications, poses many challenges in many heat-generating applications. This can lead to hot spots or even to an increase in the device temperature. Along with the increasing demand for plastics in areas of the lighting technology or in the automotive field due to the free shaping potential, the requirements are becoming more challenging. Driven by the trend of miniaturization, applications with high heat generation often have to operate in the tightest of spaces. Since not always sufficient space for complex cooling systems is given, the housing or the substrate should assume the task of thermal management. In regard to this fact, the use of thermally conductive thermoplastics seems to be very appealing. Quality loss, poorer reliability, loss of performance, and even failure can occur in case of insufficient heat dissipation. In order to improve the properties of these polymers, highly heat-conducting fillers are added in order to improve the thermal conductivity of the compound. Another technology trend that has been prevalent for years is the use of simulations. Due to shorter product life cycles and therefore shorter development times, simulation has become an indispensable part of the chain of product development. Time-consuming and costly test series make the simulation more and more important as a tool for material and product design. In this context, this paper presents a novel approach for reliability investigation and lifetime estimation, based on simulation. Therefore, a simulative method based on coupling the results from the process simulation (injection molding simulation) to finite element analysis was developed and explained. This coupled method makes it possible to take into account the manufacturing process and its engendered filler orientation. The obtained findings are compared to conventional thermal steady-state analysis and used in order to better predict the lifetime of LEDs mounted on thermoplastic substrates, the so-called molded interconnect devices. It is demonstrated that it is necessary to consider the filler orientation, especially in the case of 3D substrates.

Zusammenfassung

As miniaturization is an important aspect in all areas of circuit technology, highest demands are placed on optimum space utilization and the reduction of material and production cost. MID (Molded Interconnect Devices or Mechatronic Integrated Devices) are already broadly used in consumer electronics antennas, automation, automotive and medical technology, however MID have unexploited potential for high-frequency and fast-paced systems in particular. This work will present the design and manufacturing process of MID for RF (Radio Frequency) applications and provide RF relevant characteristics for substrate materials used in the LPKF-LDS (r)(Laser Direct Structuring) process. Furthermore, characteristics of the circuits on the injection molded plastic part, optimization of vias and interconnection geometries for hybrid assemblies will be discussed

Zusammenfassung

Silicon photonics has become a promising technology for fabrication of compact, highly integrated systems. When dealing with phase sensitive silicon photonic components, however, temperature control and in particular, reduction of temperature gradients across phase sensitive components becomes crucial. Solid-state optical beam steering using optical phased arrays (OPAs), is an exemplary system, which could be miniaturized by using silicon photonics and where temperature control is of utmost importance. In order to reduce the system cost and size as well as to increase the steering velocity, it is desired to replace mechanical beam steering systems by solid-state steering systems. Due to their compatibility with CMOS fabrication processes, silicon photonics based OPAs are promising candidates to become the next generation beam steering solution. However, due to the large thermo-optic coefficient of silicon, these phased arrays are extremely sensitive to temperature. Thermal management of silicon-photonic based OPAs requires not only heat dissipation of integrated active components, but also reduction of temperature gradients across the phased array. Here a novel concept for thermal management of silicon photonic OPAs is proposed and analyzed using finite-element simulations. The proposed concepts show a formidable efficiency in improving the heat dissipation as well as in reducing temperature gradients across the array.

Zusammenfassung

Micro manufacturing is dealing with the fabrication of structures in the order of 0.1 to 1000 µm. The scope of nano manufacturing extends the size range of manufactured features to even smaller length scales: below 100 nm. A strict borderline between micro and nano manufacturing can hardly be drawn, such that both domains are treated as complementary and mutually beneficial within a closely interconnected scientific community. Both micro and nano manufacturing can be considered as important enablers for high-end products. Especially, such products are enabled by micro and nano features and structures to incorporate special optical, electronic, mechanical, fluidic or biological functions into existing and new emerging products, and thus lead to unique selling points. Application fields include, but are not restricted to, precision instrumentation, sensors, metrology, energy harvesting, mechatronic systems, transport, medical technologies and life sciences. This Special Issue is dedicated to recent advances in research and development within the field of micro and nano manufacturing. The included papers report recent findings and advances in manufacturing technologies for producing products with micro and nano scale features and structures as well as applications underpinned by the advances in these technologies. In particular, the Special Issue covers the following topics: •Micro fabrication technologies, process chains and process characterization; •Novel product designs, micro-assembly technologies and micro-handling; •Surface engineering and interface nanotechnology; •Process modeling and simulation; •Processing and characterization of nanomaterials; •Micro and nano additive manufacturing technologies; •Micro and desktop factory concepts, systems, components and modules; •On-line monitoring and inspection systems/methods; •Applications of micro and nano technologies.

Zusammenfassung

Micro manufacturing involves dealing with the fabrication of structures in the size range of 0.1 to 1000 µm. The scope of nano manufacturing extends the size range of manufactured features to even smaller length scales—below 100 nm. A strict borderline between micro and nano manufacturing can hardly be drawn, such that both domains are treated as complementary and mutually beneficial within a closely interconnected scientific community. Both micro and nano manufacturing can be considered as important enablers for high-end products. This Special Issue of Applied Sciences is dedicated to recent advances in research and development within the field of micro and nano manufacturing. The included papers report recent findings and advances in manufacturing technologies for producing products with micro and nano scale features and structures as well as applications underpinned by the advances in these technologies.

Zusammenfassung

A novel optical incremental and absolute encoder based on an opto-ASIC and an encoder disk carrying micro manufactured structures is presented. The opto-ASIC contains a ring of photodiodes that represents the encryption of the encoder. It also includes the analog signal conditioning, the signal acquisition, a control of the light source as well as the digital position processing. A laser diode is assembled in the center on top of the opto-ASIC together with a micro manufactured polymer lens. The latter is fabricated using ultra precision machining. The encoder disk was fabricated using micro injection molding and contains microstructures forming a Blaze grating. This way a 10 bit optical encoder with a form factor of 1cm³ was realized.

Zusammenfassung

Faster Product Lifecycles make investments in machines for micro assembly riskier. Therefore, reconfigurable manufacturing systems gain more and more attention. But most customers are uncertain, if a reconfigurable manufacturing system can fulfil their needs. In this paper a novel approach for a product development method is given, which incorporates lean development methods for agile processes and focus on the conceptual design phase to overcome the customers uncertainty in the development process. For this a general representation of the conceptual design is established and validated by a team of experts.

Zusammenfassung

In the field, electronic devices are often experiencing switching cycles. With the trend of miniaturization and electrification, automotive electronic packages are facing increasingly critical reliability issues regarding current stressing and the accompanying Joule heating. In this work, the load capability of two surface-mounted shunt components subjected to cyclic current pulses is investigated. Asymmetric self-heating due to the Peltier effect is observed with infrared thermography in one of the shunt components, which leads to polarity in the microstructural evolution influencing the failure mode in the solder joint. Finite element method (FEM) is utilized to simulate the coupled electrical, thermal and mechanical fields in the assembly and to assess the response of the solder joints exposed to power cycling. Lifetime data are collected and statistically analysed based on the Weibull distribution.

Zusammenfassung

Laser induced selective activation and metallization of ceramics is a novel additive metal plating process enabling the application fine metallic paths or metallic surfaces on complex three-dimensionally shaped ceramic substrates. Metal deposition by electroless plating occurs selectively where the substrate has been locally activated by a preceding selective laser activation. The main influences on the process are the ceramic substrate material, its microstructural and optical properties as well as the laser type, laser process parameters and metallization parameters. Recent positive results with activation by a green picosecond laser were obtained only with oxygen vacancy containing alumina substrates sintered in hydrogen atmosphere. In order to be able to apply inexpensive conventional state-of-the-art sintering in air it was tried to modify the composition by doping with different oxides. 2 mass-% of fine particles of neodymium-, manganese-, samarium-, chromium-, nickel- iron-, ceria- and antimony doped tin-oxide were introduced into an alumina matrix by mixing and milling. Slip cast samples were sintered at 1500°C in air and machined. Laser activation was performed on polished sample surfaces using a Nd:YVO4 laser with a wavelength of 532nm and a pulse length of 10 ps. Electroless plating was performed with commercially available copper electrolytes. Microstructural properties, laser-matter interaction and metallization effectivity were investigated. Doping of alumina substrates with antimony doped tin-oxide, chromium-, iron- and nickel-oxide results in very good metallization of laser activated areas. Dopants enable plating larger areas and writing fine circuit paths to integrate microelectronic devices. Other additives were ineffective. The activation mechanisms triggered by the dopants is not fully understood yet. Separation and identification of single mechanisms of the dopants is required. The influence of dopants and laser activation on the mechanical properties is to be studied.

Zusammenfassung

Micro lens arrays (MLA) are broadly used in a multitude of optical applications, whereas increasingly extended areas need to be structured. Furthermore, growing quantities of microoptical components require micro- and nano-replication techniques, such as injection moulding and injection compression moulding. Therefore, ultra-precision milling strategies for manufacturing of mould inserts have been evaluated regarding applicability, surface quality and processing time. Different milling strategies were investigated regarding processing time and resulting surface quality. Single flute diamond milling tools were used to mill the mould cavities in nickel-phosphorus (NiP) coating deposited on tooling steel. The experiments were conducted on a 5-axis ultra-precision milling machine and qualitative results regarding observed effects of the different strategies were evaluated. The achieved surface qualities were analysed and quantified using white light interferometry. Methods of ring, radial or spiral milling strategies showed different failure modes and shortcomings such as stepping, pin residues or long processing times. Using a method, where a specifically designed milling tool was immersed in a single step into the bulk material, best results were achieved and the processing time for each lens was reduced to a minimum. The quality of the MLA could be further increased by immersing the milling tool in a defined angle. It was observed, that the centering and radius of the diamond of the milling tool was a major factor. Conclusively, the results show that high quality tooling in combination with the applied milling strategy enables significant improvements in quality and costs.

Zusammenfassung

In this work, a polymer microlens array (MLA) for a hyperspectral imaging (HSI) system is produced by means of ultraprecision milling (UP-milling) and injection compression molding. Due to the large number of over 12,000 microlenses on less than 2 cm², the fabrication process is challenging and requires full process control. The study evaluates the process chain and optimizes the single process steps to achieve high quality polymer MLAs. Furthermore, design elements like mounting features are included to facilitate the integration into the final HSI system. The mold insert was produced using ultraprecision milling with a diamond cutting tool. The machining time was optimized to avoid temperature drifts and enable high accuracy. Therefore, single immersions of the diamond tool at a defined angle was used to fabricate each microlens. The MLAs were replicated using injection compression molding. For this process, an injection compression molding tool with moveable frame plate was designed and fabricated. The structured mold insert was used to generate the compression movement, resulting in a homogeneous pressure distribution. The characterization of the MLAs showed high form accuracy of the microlenses and the mounting features. The functionality of the molded optical part could be demonstrated in an HIS system by focusing light spectrums onto a CCD image sensor.

Zusammenfassung

The fabrication of microstructured polymer optics enables a multitude of new options in the design of technical optics. However, challenges arise along the varying process chains of mold insert fabrication, integration into molding tools, replication by means of injection compression molding and metrology. In order to study the effects, diffractive optical elements (DOE) and micro lens arrays (MLA) are fabricated using two different process chains. DOEs are fabricated using a laser direct writing (LDW) based mold insert fabrication. The MLA mold insert is produced using ultraprecision milling (UP-milling). Both optical parts are replicated using injection compression molding. The occurring effects are discussed and the results show, that with complete process control high quality microstructured polymer optical parts can be produced and characterized.

Zusammenfassung

Polymer optics are widely used in various applications, replacing traditional glass lenses. The ability to create free-form and micro-structured optics, as well as fast replication, gives them major advantages over traditional glass lenses. However, the fabrication of complex optical components requires full process control and understanding of influencing factors on the quality of the polymer optical parts. In this work, a curved diffractive optical element (DOE) is fabricated using injection compression molding. Different gate designs were evaluated and the movement of the compression stamper was optimized to obtain good filling behavior. The process stability was analyzed and improved by controlling the melt temperature precisely. Finally, the molding parameters were optimized, focusing on the mold temperature, melt temperature and compression force. Curved diffractive optical elements were replicated with feature sizes of 1.6 μm. The experiments showed that all aspects of the molding process have to be controlled perfectly to produce complex polymer optics. High mold temperatures and compression force are necessary to replicate micro-structured features. The work presents a broad investigation and description of the fabrication process and their influences.

Zusammenfassung

Light-emitting diodes (LEDs) have increasingly replaced conventional lamps in the fields of general lighting and consumer electronics. In addition to the sharp price fall, this is also due to the significantly higher energy efficiency and the smaller, more compact design. Recently, their robustness and reliability have also reached a level of quality that surpasses the characteristics of conventional light sources such as halogen and fluorescent lamps. Characteristics, such as excellent design freedom and the possibility for functional integration, highlight the main qualities of molded interconnect devices (MIDs). The use of this technology does not only open doors to extend the application field of LEDs to new products but also presents challenges to the lighting industry. There are many studies dealing with the reliability of LEDs as well as with the usability of the MID technology in different fields. But, the lack of experience from the manufacturers regarding the behavior of this interesting configuration (LED/MID) over the entire life cycle prevents this technology from establishing and consolidating its existence. As LEDs in the automotive sector, especially within headlamps, assume increasingly powerful lighting tasks and are no longer used exclusively for signal transfer or for displays, thermal properties of the substrate materials and the thermo-mechanical behavior of the assembly are particularly relevant. In this context, this paper presents a deep and detailed reliability investigation of this system (LED/MID) and examines the influence of the MID substrate choice on the long-term performance of the LED. The impact of the forward current and of the ambient temperature on the junction temperature of the LED is a proven fact. Therefore, the MID effect was inspected under different operating conditions based on infrared thermography. After analyzing the occurred failure mechanisms, by means of X-ray analysis, thermal transient testing and microscopy, the resulting lifetime model is also presented and discussed.

Zusammenfassung

Higher energy efficiency, more compact design, and longer lifetime of light-emitting diodes (LEDs) have resulted in increasing their market share in the lighting industry, especially in the industries of consumer electronics, automotive, and general lighting. Due to their robustness and reliability, LEDs have replaced conventional light sources, such as fluorescent lamps. Many studies are examining the reliability of LEDs as such or investigating their long-term behavior on standard printed circuit boards (PCB). However, the thermal performance of LEDs mounted on nonconventional substrates is still not explored enough. An interesting example for this is the molded interconnect devices (MID), which are well known for the great design freedom and the great potential for functional integration. These characteristics not only underline the main abilities of the MID technology, but also present some challenges concerning thermal management. The long-term behavior of LEDs on MID is still quite untapped and this prevents this technology from consolidating its existence. In this context, this work highlights a developed test setup aimed at investigating LEDs, mounted on molded interconnect devices, under combined stress conditions. The results of the reliability study, as well as the resulting lifetime model, are also illustrated and discussed.

Zusammenfassung

A Physical Unclonable Function uses random and inherent properties of a physical entity and can be used to uniquely identify components e.g., for anti-counterfeiting purposes. In this work we demonstrate that the surface patterns of injection moulded plastic components themselves are inherently unique and hence can be used as a PUF for reliable and secure identification. We further demonstrate that these unique surface patterns are easily accessible since they can be photographed with a simple camera set-up. This is exemplarily demonstrated for two different plastic materials on an overall of 200 injection moulded components. A set of brief experiments further examines the PUF's robustness towards real life conditions. This approach might be useful for secure identification and authentication of components or a label-free tracking.

Zusammenfassung

Individual traceability of components enables efficient quality control, improving operational efficiency, or smart manufacturing approaches like big data analysis as well as customized mass production. Conventional track and trace solutions however, require a tag or label which is often not attachable due to e.g., spatial or economic reasons. A promising alternative is the identification of components based on individual, inherent surface patterns. For a set of 115 printed circuit boards, it is shown that fiducial markers, which are commonly used for alignment of components, can possess such individual surface patterns and hence serve as unique identifier. As the investigations are based on industrial conditions, the paper transfers the approach of label-/tag-free traceability from laboratory to an application in an industrial environment. Furthermore, faultless traceability of all samples within a SMD assembly line is achieved demonstrating the robustness of the identification against changes of the surface.

Zusammenfassung

With the introduction of lead-free solder alloys, the effect of voids on solder joint reliability has rapidly gained importance. In this study, a first analysis of X-rayed CR0805 solder joints shows a significant reduction in void content, from 20% down to 2.5%, after vacuum soldering. The statistical analysis of the void distribution demonstrates that the vacuum option reduces number of voids and median diameter of voids in comparison to the convection soldering process. A subsequent accelerated thermal cycling test of these analysed test vehicles, according to JESD22-A104D, indicates the tendency of a higher characteristic life time for higher void content. In contrast to these findings, the 1% to failure criterion reveals a higher reliability for lower voiding. During the finite element method (FEM) modelling part of this study, two modelling approaches of void implementation into solder joint geometry are investigated: modelling with a constant volume of the standoff for different void contents, and a modelling approach with a random combination of void content and volume of standoff. The modelling approach with the random combination reveals that voids can reduce the lifetime in the “worst case” parameter combination. In particular, the 1% time to failure rate indicates a quantitative correlation with the experimental results. Furthermore, the FEM results suggest a higher impact on reliability for a single void in comparison to a distribution of multiple voids with similar void content. Finally, the FEM study shows a high sensitivity of predicted life time with respect to the standoff height. Based on this finding, the CR0805 solder joint geometry is examined using optical inspection and cross-section polishes with the outcome that the better wetting behaviour during vacuum soldering causes a reduction of the solder alloy volume and consequently further decreases the standoff height.

Zusammenfassung

Molded interconnect devices (MID) offer great potential for circuit board applications, especially regarding three-dimensional shaping and functional integration. Applying circuits to polymer substrates can be performed by means of laser patterning methods. In these, the matrix polymer is filled with a special metal additive, enabling laser activation and subsequent metallization. Important effects emerge during processing of the matrix polymer. In this work, the influence of the gate geometry and the resulting flow behavior during injection molding on the quality of the metallization is investigated.

Zusammenfassung

Packaging represents an important part in the microintegration of sensors based on microelectromechanical system (MEMS). Besides miniaturization and integration density, functionality and reliability in combination with flexibility in packaging design at moderate costs and consequently high-mix, low-volume production are the main requirements for future solutions in packaging. This study investigates possibilities employing printed circuit board (PCB-)based assemblies to provide high flexibility for circuit designs together with film-assisted transfer molding (FAM) to package sensors. The feasibility of FAM in combination with PCB and MEMS as a packaging technology for highly sensitive inertia sensors is being demonstrated. The results prove the technology to be a viable method for damage-free packaging of stress- and pressure-sensitive MEMS.

Zusammenfassung

Cost-effective electronic packaging technology plays a vital role in the manufacturing industry with ever increasing demand for microelectronics and microsystems. The application of thermoset encapsulation of electronic parts offers a wide range of advantages with respect to thermal, mechanical and chemical properties. Transfer Molding, mainly available in the Far East, is dominantly used for the manufacturing of such polymeric packages 2. Thermoset injection molding extends a good scope of advantages over transfer molding like availability in Europe and ease of raw material handling. The implementation of thermoset injection molding for encapsulation of electronic components provides the European small and medium-sized enterprises (SMEs) with access to customized packaging solutions. The feasibility of this implementation is defined and tested in this work.

Zusammenfassung

Reliability aspects are crucial for the success of every technology in industrial application. Regarding interconnect devices, several methods are applied to evaluate reliability of conductor paths like accelerated environmental tests. Especially, molded interconnect devices (MID), which enable numerous applications with three-dimensional (3D) circuitry on 3D shaped injection-molded thermoplastic parts are often under particular stress, e.g., as component of a housing. In this study, a new test method for evaluating the flexural fatigue strength of conductor paths produced by the laser-based LPKF-LDS® technology is presented. For characterization of test samples, a test bench for flexural fatigue test was built up. A result of the flexural fatigue test is a characteristic Woehler curve of the metal layer system. Applying this new test method, essential influencing parameters on the reliability of MID under mechanical load can be identified. So, the metal layer system as well as the geometric parameters of the metal layer is crucial for the performance. Furthermore, test specimens are tested under different types of mechanical load, i.e., tensile stress and compressive stress. For a holistic view on reliability of MID, experimental results are discussed and supported by simulations. An important finding of the study is the advantage of nickel-free layer systems in contrast to the Cu/Ni/Au layer system, which is often used in MID technology.

Zusammenfassung

This chapter is meant to give an overview of capabilities and limitations of inkjet printing of functional structures on molded 2D and 3D substrates. Different injection-molded thermoplastics, transfer molded thermosets, and polyimide (PI) foil were used as substrate materials. Conductive structures were obtained by inkjet printing of commercially available silver nanoparticle inks. Results on inkjet-printed structures and devices such as temperature sensors, intrusion sensor conductor loops, or electrical interconnects and antennas on transfer-molded packages will be presented. Methods for the electrical interconnection of the printed structures with nonprinted conductive structures such as PCB contact pads are also discussed.

Zusammenfassung

Winkelmessung auf engstem Raum war bisher eine kaum lösbare Aufgabe. Insbesondere, wenn ein optisches Verfahren angewendet werden soll und eine hohe Auflösung benötigt wird, ist bisher keine zufriedenstellende Lösung zu finden. Hahn-Schickard hat in Zusammenarbeit mit dem IMS Chips einen neuen Ansatz zur Lösung dieser Aufgabe gefunden.

Zusammenfassung

Since the introduction of lead-free solder alloys, the impact of voids in solder joints has rapidly gained in importance. Particularly in power electronics, voids in solder joints can reduce their reliability due to less heat dissipation and a significant reduction of the cross-sectional area. While void formation in the printed circuit board (PCB) technology has been the focus of many research projects, the increasing application of molded interconnect devices (MIDs) demands a vivid understanding of void formation and its impact on reliability. This report will show that those processes specific to MID technology do not significantly influence the void formation in SAC305 solder deposits. The processed different roughness levels on Vectra, Vestamid, and FR4 substrate materials show no significant impact on void formation. The surface finish metallization was detected as the most important factor. Especially, the chemical-Sn (iSn) surface finish is inclined to having more voids compared to a nickel-phosphor-gold (NiP-Au) finish. Furthermore, three solder processes were investigated: convection, condensation, and vacuum-condensation soldering. The vacuum-condensation processes significantly reduced the voids in the Sn-3.0Ag-0.5Cu (simplified as SAC305) solder joints of CR0805, MLF20, and switches on all the investigated substrates. An accelerated thermal cycling test of these components according to JESD22-A104D demonstrates no significant effect of the void content of <;19% on the solder joints' reliability. Finally, the result of accelerated thermal cycling shows the possibility to achieve an equivalent lifetime of the solder joints on Vectra in comparison to the FR4 substrate.

Zusammenfassung

Micro technology deals with the fabrication of structures in the length scale between 0.1 and 1000 µm and can be considered as an important enabler for micro systems such as miniaturized sensors. Recent advances in micro manufacturing will be demonstrated by examples of microfluidic, optical and mechatronic devices. In the area of microfluidics, the fabrication of centrifugal microfluidics for automated analytics and diagnostics via injection compression molding is addressed. Manufacturing of optical components via micro injection molding and precision assembly of those components will be presented with respect to optical sensors. Molded interconnect devices serve as an example for the manufacturing of mechatronic devices. Apart from manufacturing technologies, the application of simulation methods for the assessment of manufacturability and reliability of the devices will be discussed.

Zusammenfassung

This paper focuses on packaging of small-scale thermoelectric generators (TEGs) for energy harvesting applications in sensor nodes for industry 4.0 and for the Internet of Things. The TEGs are suitable to enable self-powered sensor systems with unlimited energy lifetime, but they have to withstand high mechanical loads during the assembly and packaging process and further stress due to the mismatch of the coefficient of thermal expansion of the different materials. Devices with different underfills (UFs) and stress decoupling thermal adhesives were evaluated with a shear force test apparatus and a four-line bending test together. In addition to these mechanical tests, the thermal influence of the UF on the system performance was investigated with measurements, finite element method, and computational fluid dynamics simulations. The shear force per area could be enhanced up to the factor of two by using capillary UF. All TEGs with and without UFs passed the reliability investigations without any electrical defects. All TEGs with UF passed the given quality criteria with the four-line bending test. With some of the stress decoupling thermal adhesives, the TEGs could withstand the loads without UF. The simulation model was evaluated with a measurement setup, and the differences between the simulation model and the measurements concerning the temperature difference of the TEGs were in an acceptable range (<;21%). Furthermore, the influence of the UF on the temperature difference of the TEGs in the given measurement scenario was smaller than 15%, which makes the application of a UF a realistic approach.

Zusammenfassung

Molded Interconnect Device (MID) Technology features excellent design freedom and great potential for functional integration for applications in indoor lighting. Spatial arrangement of LEDs and intelligent control elements enable highly efficient, situation aware lighting concepts with attractive design. Even more than in PCB based LED lighting technologies, there are significant degrees of freedom for improved thermal management when designing and manufacturing an MID. In this work, measures suitable for thermal management of MID for lighting applications manufactured with LPKF-LDS® technology are identified and compared. Focus is on design for thermal management and application of recently developed high thermal conductivity polymers. To compare the effects of the different measures, simulations are performed with a range of combinations of individual measures for thermal management. The simulation results of the individual combinations are evaluated using design of experiments statistical methods. Low cost measures relying on design for thermal management are compared to measures implying higher manufacturing costs and to substrates manufactured from high thermal conductivity polymer compounds.

Zusammenfassung

Räumlich gestaltete mechatronische Systeme wie z.B. dreidimensionale spritzgegossene Schaltungsträger (Moulded Interconnect Devices - MID) sind heute, oft unsichtbar für den Endanwender, Bestandteil vieler Produkte. Die Freiheiten der räumlichen Formgebung des Spritzgusses mit einer Vielzahl von elektrischen, aber auch optischen, mechanischen oder fluidischen Funktionen zu kombinieren bietet einzigartige und bestechende Möglichkeiten.

Zusammenfassung

Reliability aspects are crucial for the success of every technology in industrial application. Regarding interconnect devices, several methods are applied to evaluate reliability of conductor paths like accelerated environmental tests. Especially Moulded Interconnect Devices (MID) which enable versatile applications with 3D circuitry on 3D shaped injection moulded thermoplastic parts are often under particular stress, e.g. as component of a housing. In this paper a new test method for evaluating the flexural fatigue strength of conductor paths produced by the laser based LPKF-LDS® technology is presented.