# Additive Manufacturing for Automotive Radar Sensors Using Copper Inks and Pastes
## 4 Conclusions  
This study demonstrated the feasibility of additively manufacturing metal traces as heating structures directly onto the radome of radar sensors. Several additive manufacturing (AM) technologies were evaluated, including fused deposition modeling (FDM), inkjet printing of metal particle-free inks, and dispensing of inks and sinter pastes. FDM, while a productive AM technology for plastic parts, revealed that, so far, no sufficient highly electrically conductive filaments are available. However, further material development is required before FDM can be effectively implemented for printing conductive traces in the near future. This caused the exploration of alternative AM methods for printing the heating structure, utilizing a copper complex ink and a copper paste. Low-cost copper materials are very promising for the AM of electrical wiring, as the material costs significantly impact the AM costs. Both the copper complex ink and copper paste were successfully printed, achieving the targeted specific electrical resistance of below 10 \(\upmu\Omega\)cm. The pressureless oven sintering of the copper traces still exhibited limitations concerning the adhesion of the trace to the substrate. Further material and process development is ongoing to enable the application of pastes and inks without pressure. However, pressureless laser sintering was identified as an effective process, yielding the lowest specific resistivity (3.25 \(\upmu\Omega\)cm) and the best adhesion. Based on these findings, the laser sintering of copper structures using the available copper materials is ready for implementation in patterning traces on 3D polymer structures. Automated AM machines, such as 3D dispensers or inkjet printers with integrated lasers, are readily available. The processing times for creating the heating structures are sufficiently fast, allowing these machines to be integrated into automated assembly lines for sensors.  
Conceptualization, N.M. and G.E.; methodology, N.M.; software, N.M.; validation, N.M., F.S. and G.E.; formal analysis, N.M.; investigation, N.M., F.S. and G.E.; resources, S.W., H.E. and G.E.; data curation, N.M., F.S. and G.E.; writing--original draft preparation, N.M. and  
Figure 9: SEM image of laser-sintered copper layer.  
G.E.; writing--review and editing, N.M., F.S. and G.E.; visualization, N.M. and G.E.; supervision, G.E.; project administration, H.E. and G.E.; funding acquisition, H.E. and G.E. All authors have read and agreed to the published version of the manuscript.  
This research \"Additive Fertigung zur Miniaturisierung Hochperformander und Robuster Radarsensoren--ADDIRA\" was funded by Bayerisches Staatsministerium fur Wirtschaft, Landesentwicklung und Energie under grant number DIE-2107-005//DIE0159/01.  
Not applicable.  
Data Availability Statement: Data are contained within the article.  
The authors would like to thank [PERSON] from Conti Temic microelectronics GmbH, Ingolstadt, and [PERSON] and [PERSON] from the University of Applied Science Ingolstadt for their support of the project. The authors thank [PERSON] for providing the copper engineering paste for testing in pressureless sintering applications.  
Authors [PERSON] and [PERSON] were employed by the company \"Continental Autonomous Mobility Germany GmbH\". The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.