Isothermal Fatigue of Interconnections in Flexible Hybrid Electronics Based Human Performance Monitors

The development of reliable Flexible Hybrid Electronics (FHE) that are light, wearable and conforming to the human body while still preserving full operational integrity requires among other an understanding of the fatigue behavior of interconnects such as traces on flexible substrates (Polyimide, Polyethylene Terephthalate, etc.). There are different loading modes of potential concern, such as tension, bending and peeling. The present study addresses effects of tension on aerosol printed AgNP (silver nano-particles) traces. These traces are nano-porous and as such inherently brittle, but the presence of a flexible substrate has major effects on their behavior. Electroplated Cu traces are included for reference. Major increases in electrical resistance were observed for even minor deformation but inspection by SEM did not reveal any damage, and the presence of the substrate prevents the detection of changes in trace properties through direct measurement of deformation vs. the applied loads. Studies of the evolution of damage were therefore limited to characterization of the resistance vs. variations in strain. Interpretations of results were further complicated by the time-dependent viscoelastic deformation of the substrate. Nevertheless, systematic trends are appearing.