Flexible printed circuits (FPCs) are widely used in electronic devices such as movable part line or wearable sensor. Photolithography is one of the most popular processes for fabricating electric interconnect lines. However, inkjet printing has attracted attention because the method can draw an arbitrary-shape electric lines without any mask. Therefore, nanoparticle metal ink is widely used for printing of conductive electric lines with lowering cost and small-lot production. The physical characteristics such as flexibility or durability of metal nanoparticle ink lines have been evaluated by bending or tensile tests. By contrast, the evaluation method has not been sufficiently established for the electrical characteristics of these lines, and the failure mechanism under high-current density has not been clarified. According to scaling down of electric devices, current density and Joule heating in device lines increase and electromigration (EM) damage becomes a serious problem. EM is a transportation phenomenon of metallic atoms caused by electron wind under high-current density. Reducing EM damage is extremely important to enhance device reliability. In this study, current loading tests of metal nanoparticle ink line were performed to discuss damage mechanism and evaluate electrical reliability under high-current density condition.
As the results of current loading tests, the thickness of cathode part of straight-test line was decreased. It is considered that atomic transport from the cathode to the anode occurred by EM phenomenon. The line surface became rough and aggregates of particles generated at middle or anode parts of straight-test line by high-current loading. Both of atomic transport and aggregate generation were closely related the changes of potential drop, their dominances were varied depending the current density value.