Fabrication Techniques for Multilayer Printed Flexible Hybrid Sensor Systems

Additive manufacturing holds the potential to revolutionize circuit fabrication and enable the widespread adoption of printed electronics, particularly in flexible applications, such as wearable or conformable electronic sensing systems. However, realizing practical circuits with multilayer interconnects or vertical interconnect accesses (VIAs) using additive methods, flexible substrates pose significant challenges. In this study, we systematically evaluate four different methods for fabricating VIAs in flexible printed circuits: soldered, printed, conductive epoxy, and zero-ohm jumper VIAs. Through comprehensive testing involving various levels of bending strains, we measure changes in conductive properties and mechanical integrity to validate each method. Our results indicate that printed VIAs exhibit the most desirable properties compared to other methods, with a baseline resistance of approximately $0.9~\Omega $ and a change of approximately 7% when subjected to a bending radius of 12 mm. Additionally, cyclic bending tests and tensile strength test were exclusively carried out on the printed VIAs to evaluate their resilience under bending and tensile strains. Leveraging the superior performance of printed VIAs, we successfully manufacture a fully conformable impact sensing system capable of adhering to a sports ball, thereby demonstrating their effectiveness in practical applications. This study underscores the utility and potential of multilayer flexible PCB fabrication using additive printing technology, highlighting its significance in advancing the development of innovative electronic systems with enhanced flexibility and reliability. The findings presented herein offer valuable insights into the optimization of VIA fabrication methods and their implications for the design and deployment of flexible electronic devices in diverse real-world scenarios.