Effects of Strain Rate and Dwell Time on Fatigue Damage Accumulation in Aerosol Jet Printed Nanosilver Traces on Flex

Sintering of aerosol jet printed nano-Ag traces leads to nanoporous structures that are macroscopically brittle, but the reduction in strain localization offered by the support of a flexible polyimide substrate means that the traces are still quite flexible and can withstand much higher strains than the free-standing structures. The resulting behavior under cyclic loading conditions is very different from what we are used to for conventional microelectronics interconnects. As a part of an ongoing systematic effort, the present work is focused on the effects of strain rates and brief dwells, either between loads or at the maximum strain. Lower strain rates led to more damage per cycle, but the effect of slower unloading was greater than the effect of slower loading. Interestingly, although ongoing work shows an hour-long dwell at zero loads to allow for some degree of recovery and, thus, longer life, dwells on the order of minutes led to more damage per cycle. In contrast, short dwells at the maximum strain led to less damage in subsequent cycling. All of this can be rationalized in terms of an emerging phenomenological picture.