Cyclic Bending Effects on Resistance of Screen-Printed Silver Conductors

Flexible electronics are becoming more and more widely used in all fields, such as wearable devices, flexible displays, flexible sensors, and so on. Therefore, it is essential to investigate the reliability of flexible electronics under various loading conditions. In this article, the mechanical and electrical behavior of printed conductors was tested under reciprocating adaptive curvature flexure bending. The silver-ink conductors of different widths were screen-printed on polyimide (PI) and polyethylene terephthalate (PET) substrates and served as the samples. Through the tests, the resistance of the conductors was measured by a four-wire method continuously. The tests were carried out under different gap distances and moving ranges. Besides the tests, SEM imaging was also performed to understand the microstructure change of the printed conductor before, during, and after the tests. Finite-element simulations were performed to track the strain history of specific locations of the printed conductor. Finally, a two-stage process of resistance increase was identified in the reciprocating adaptive curvature flexure test. The resistance change of the conductors under different loading conditions was determined. The parameters that affect the resistance change were also figured out. Cracks and delamination in the printed conductor were observed and related to the resistance increase phenomena under small tensile and compressive bending radius, respectively.