Wearable electronics need a number of desirable attributes, such as being compact, flexible, and lightweight. Prior studies on reliability testing have examined the relationship between a flexible electronic and repetitive human body motions (i.e., stretching, bending, twisting, and folding). Such mechanical loads can cause fatigue failure in a wearable electronic. In regard to a wearable band, fatigue failure can be influenced by folding stress. This research study involved the assessment of wearable biometric bands that were calibrated and examined by a test device for folding reliability. The wearable band combines a biometric sensor unit, a micro-controller unit with a wireless connection, and a printed thermistor unit. The sensors have been calibrated by actual temperature and biometric signals. Furthermore, the folding test was conducted utilizing multiple boards. Due to multiple components and printed lines of the PCB, optical images were taken in order to confirm which parts failed and the reasons for the failures. An FEM analysis was conducted in order to understand how stress impacts the PCB and which parts are stressed during the folding process. Throughout the process, an equation was developed to predict the number of cycles necessary for reaching fatigue failure. Throughout this study, the fatigue failure analysis on folding reliability of the wearable biometric band was conducted using experimental analysis, microscopy analysis, and simulating analysis. The study provided further knowledge about the fatigue failure mechanism, which resulted from the prediction of fatigue life developed from the PCB.

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