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Evaluation of an Anisotropic Conductive Epoxy for Interconnecting Highly Stretchable Conductors to Various Surfaces

Stretchable wearable electronics often require integrating mechanically different materials to fabricate functional devices that are stretchable, conformal, and sufficiently reliable. Common methods to integrate highly stretchable conductors with other Flexible Hybrid Electronics (FHE) components include solder and isotropic/anisotropic conductive adhesives or films. Due to the nature of the stretchable conductors/substrate, each of those methods has its limitations in wearable and stretchable devices. A magnetically aligned Anisotropic Conductive Epoxy (ACE) has promising potential for such integration due to its excellent adhesion to most substrates of interest, low curing temperature, and no pressure processing requirements. This study investigates the effect of the mechanical and environmental stresses on a magnetically aligned ACE as a bonding material between polymerized liquid metal networks (Poly-LMNs) and copper, e-textile, and Surface Mount Device (SMD) resistor. The test coupons were subjected to various mechanical and environmental stresses through a tensile test, fatigue cycling, and exposure to temperature and humidity conditions. The results showed that the ACE exhibited robustness and low contact resistance during electromechanical testing. In addition, the Poly-LMNs to e-textile or Cu-Flex assembly through magnetically aligned ACE showed no noticeable increase in the electrical resistance from cycle to cycle during fatigue cycling. The environmental conditions showed no significant impact on direct contact joints; however, there was a permanent failure to via connections due to moisture absorption, which led to cracks/delamination.