Method for Assessment of Folding-Reliability of Flexible Electronics in Wearable Applications

There is a growing need for flexible hybrid electronics solutions for wearable applications, in which the user may often wear electronics on body, on fabric or on skin. Electronics in wearable application may be subjected to stresses of daily motion including bending, twisting and stretching. Thus, there is need for technologies capable of flexibility, robustness and small size while being lightweight. Existing standards for focus on rigid electronics and there is scarcity of guidance for test-levels needed to assure reliability of flexible electronics. There is need for studies focused on the development of accelerated test conditions representative of field applications and the identification of failure mechanisms for test levels. In this study, experimental analysis on fatigue life of the PCB in cyclical folding load is conducted. A folding test-stand capable of replicating the stresses of daily motion in a lab-environment has been developed for the test. For the better understanding of the failure mechanism, analysis of failure modes is carried out. Consequently, it is found that fatigue life of the PCB is related to the several conditions: folding direction, moving distance, folding diameter and strain rate.