The Effect of Torsional Bending on Reliability and Lifetime of Printed Silver Conductors

Capability of high-speed and low-cost manufacturing makes the printing techniques a very promising approach for large-area flexible electronics mass manufacturing. Due to fast and intensive technology development, the lack of knowledge about the reliability and lifetime of printed electronics is obvious, requiring further investigation. Especially, the effect of torsional bending on lifetime is a mostly unexplored field of reliability testing. In this article, a torsional bending test of parallel printed silver conductors (0.3-, 0.5-mm pitch) on polymer substrate (polyethylene terephthalate, 125- \mu \text{m} thickness) was conducted and analyzed. According to the experimental results, torsional bending causes wear-out type failures in conductors and the length-to-width (LTW) ratio of the sample's substrate was observed to have a significant impact on reliability. If the LTW ratio is smaller than 3, the lifetime of printed conductor seems to collapse and samples lasted for approximately only 17 bending cycles on average. Lifetime was improved by increasing the LTW ratio and samples withstood over hundreds of cycles with LTW ratio of higher than 15. However, the distance of a conductor from the edge of the substrate was not observed to have any significant influence on the reliability under torsional bending.