Bending reliability of printed conductors deposited on plastic foil with various silver pastes

The cyclic bending reliability of printed conductors fabricated with different polymer thick film pastes is studied in this article. Three silver pastes with different properties, Asahi SW1400, Asahi LS411AW, and DuPont 5064H, were utilized to deposit test specimens on a 125-μm thick polyethylene terephthalate foil, Melinex ST506, and to investigate the paste characteristics affecting the mechanical durability of the test specimens. The main fabrication method for the traces was roll-to-roll printing with a rotary screen, but also a sheet-based screen printing process was used to compare the results between the two manufacturing techniques. The electrical behavior of the test components was monitored by measuring the DC resistance of the test samples in situ under cyclic bending in both compression and tension with about a 6 mm bending radius. The reliability of the studied test populations was assessed with the statistical Weibull analysis as the failure criterion was a 20 % increase in resistance. It was found that the conductors fabricated with the paste with the smallest silver particle size, Asahi SW1400, had the highest lifetimes. This was due to the more flexible micro-scale structure with a lower volume fraction of silver in the paste. In addition, heat-treatment during the printing process was observed to be a crucial factor from the both electrical and mechanical perspectives of the printed conductors.