T. Scherzer, M. Wolf, K. Werum, H. Ruckdäschel, W. Eberhardt, and A. Zimmermann, “Dielectric Properties of PEEK/PEI Blends as Substrate Material in High-Frequency Circuit Board Applications,”
Micromachines, vol. 15, Art. no. 6, 2024, doi:
10.3390/mi15060801.
Zusammenfassung
Substrate materials for printed circuit boards must meet ever-increasing requirements to keep up with electronics technology development. Especially in the field of high-frequency applications such as radar and cellular broadcasting, low permittivity and the dielectric loss factor are key material parameters. In this work, the dielectric properties of a high-temperature, thermoplastic PEEK/PEI blend system are investigated at frequencies of 5 and 10 GHz under dried and ambient conditions. This material blend, modified with a suitable filler system, is capable of being used in the laser direct structuring (LDS) process. It is revealed that the degree of crystallinity of neat PEEK has a notable influence on the dielectric properties, as well as the PEEK phase structure in the blend system developed through annealing. This phenomenon can in turn be exploited to minimize permittivity values at 30 to 40 wt.-% PEI in the blend, even taking into account the water uptake present in thermoplastics. The dielectric loss follows a linear mixing rule over the blend range, which proved to be true also for PEEK/PEI LDS compounds.BibTeX
M. Wolf et al., “Investigation of LDS-capable PEEK/PEI Blends for Customizable Multilayer LDS-MID for Fabrication ofo Millimeter Wave-Capable High Frequency Module,” Jun. 2023.
BibTeX
M. Wolf, K. Werum, W. Eberhardt, T. Günther, and A. Zimmermann, “Injection Compression Molding of LDS-MID for Millimeter Wave Applications,”
Journal of Manufacturing and Materials Processing, vol. 7, Art. no. 5, 2023, doi:
10.3390/jmmp7050184.
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.BibTeX
M. Wolf, K. Werum, T. Guenther, L. Schleeh, W. Eberhardt, and A. Zimmermann, “Analysis of Tempering Effects on LDS-MID and PCB Substrates for HF Applications,”
Journal of Manufacturing and Materials Processing, vol. 7, Art. no. 4, 2023, doi:
10.3390/jmmp7040139.
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.BibTeX
T. Guenther, K. Werum, E. Müller, M. Wolf, and A. Zimmermann, “Characterization of Wire-Bonding on LDS Materials and HF-PCBs for High-Frequency Applications,”
Journal of Manufacturing and Materials Processing, vol. 6, Art. no. 1, 2022, doi:
https://doi.org/10.3390/jmmp6010009.
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.BibTeX
S. Seewald, D. Manteuffel, M. Wolf, M. Barth, W. Eberhardt, and A. Zimmermann, “Low-Loss 3D-Coplanar Line Structure for Millimeter Wave Applications Using Laser Direct Structuring Technology,” in
2021 International Conference on Electromagnetics in Advanced Applications (ICEAA), IEEE, 2021, p. 85. doi:
10.1109/ICEAA52647.2021.9539572.
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.BibTeX
M. Wolf et al., “Injection compression molding for manufacturing LDS-MID based millimeter wave modules,” in Proceedings of the 14th International Congress Molded Interconnect Devices, J. Franke, P. Brauer, C. Goth, A. Pojtinger, S. Landvogt, and I. Kriebitzsch, Eds., Molded Interconnect Devices 3-D MID e. V., Feb. 2021, pp. 51–75.
BibTeX
M. Wolf et al., “Optimized Micro-Mounting and Hybrid Integration of RF Mixed- Signal Systems based on MID Technology,” in Smart Systems Integration; 13th International Conference and Exhibition on Integration Issues of Miniaturized Systems, 2019, pp. 1–4.
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 discussedBibTeX
E. Ermantraut et al., “Fabrication of 3D Ceramic Interconnect Devices by Laser Induced Selective Metalization,” T. Otto, Ed., 2018.
BibTeX
V. Geneiß et al., “Impedance-Controlled Design and Connection Technology for Micromounting and Hybrid Integration of High-Frequency and Mixed-Signal Systems with MID Technology,” Apr. 2018.
BibTeX
H. Mueller et al., “Laser Induced Selective Metallization of 3D Ceramic Interconnect Devices,” in 13th International Congress Molded Interconnect Devices, Molded Interconnect Devices 3-D MID e. V., Sep. 2018, p. 328.
BibTeX
M. Wolf et al., “Investigation on the Influence of Injection Molding Parameters on High Frequency Permittivity up to 3 GHz on MID Thermoplastics and Reliability of Permittivity During Environmental Testing,” in 13th International Congress Molded Interconnect Devices, Molded Interconnect Devices 3-D MID e. V., Sep. 2018, p. 329.
BibTeX
