The Effect of Width and Thickness on Cyclic Bending Reliability of Screen-Printed Silver Traces on a Plastic Substrate

Abstract

The cyclic bending reliability of screen-printed silver traces on a plastic substrate is studied in this paper. The trace populations under study were printed, with different widths (250, 500, 1000, and 2000 $\mu \text{m}$ ) and thicknesses (12, 24, and 36 $\mu \text{m}$ ), on a 125- $\mu \text{m}$ -thick polyethylene terephthalate film and subjected to dynamic loading by a bending tester. The reliability of each test component was monitored in situ with a four-point resistance measurement, with a 20% increase in resistance as a failure criterion. The most reliable cross-sectional geometry was found to be the trace population having a thickness of 12 $\mu \text{m}$ and a width of 250 $\mu \text{m}$ with the characteristic lifetime of 1555 bending cycles. The statistical analysis proved that the long-term reliability of the studied components can be enhanced by decreasing their thickness and thus reducing the mechanical strain on the trace surface. In addition, decreasing the trace width improved the reliability due to the flattening of the trace during the manufacturing process. The failure analysis did not indicate notable changes in the trace geometry after the cyclic bending test, and the cause of failure was deduced to be deterioration of the conductor’s internal structure.