Effect of Ag agglomeration-driven nanovoids formation on fatigue reliability of Cu–Ag alloy flexible interconnects

Fatigue failure under cyclic deformation remains longstanding challenge in the flexible interconnect for the long term application. In this study, we design Cu–Ag alloy interconnects with excellent fatigue resistance by adopting nanovoid structures acquired by a simple post-annealing process. Nanovoids are generated during Ag agglomeration in the Cu matrix because of the low solubility of Ag in Cu, which enhances the fatigue property of a Cu–Ag alloy deposited on a polyimide film. The effect of high-density nanovoids located at the triple junction of the Cu and Ag grain boundaries on the mechanical fatigue lifetime is investigated by microstructure analysis (HAADF, HR-TEM and ASTAR™-coupled TEM). The fatigue damage of the Cu–Ag alloy has been observed to originate from grain boundary decohesion, unlike typical long fatigue cracks and extrusions. This can be attributed to the uniform distribution of nanovoids, which leads to stress concentration relief and consequently reduces the level of deformation.