Reliability study on adhesive interconnections in flex-to-flex printed electronics applications under environmental stresses

The reliability of conductive adhesive interconnections in flex-to-flex printed electronics applications under thermal cycling and cyclic bending tests is investigated in this paper. The components under study consisted of a backplane, having screen-printed silver wiring on polyethylene terephthalate film, fabricated in a roll-to-roll process, and a flexible functional component mimic stacked on top of the backplane. Each test component contained four daisy-chained conductive adhesive interconnections, and their reliability was monitored in situ with a four-point dc resistance measurement during tests. In addition, the effect of supportive nonconductive adhesives on structure reliability was studied in various configurations. The accelerated life test results proved that the long-term reliability of the studied components can be enhanced by adding supportive adhesive between the flexible layers. In both thermal cycling and cyclic bending tests, the most reliable method was found to be the configuration with supportive adhesive around the top layer sides, attaching the two layers totally together, whereas the configuration with no supportive adhesive at all showed the worst reliability. The failure analysis emphasized that the critical factor, in terms of reliability, was silver conductor delamination from the backplane surface at the interconnection area.