Cross-Interaction in Cu/Sn/Co/Sn/Ni and Cu/Sn–Co/Co/Sn– Co/Ni Couples

Abstract

In this study we examined cross-interactions of Cu/Co and Co/Ni by use of Cu/Sn/Co/Sn/Ni and Cu/Sn–0.04 wt.% Co/Co/Sn–0.04 wt.% Co/Ni couples. In the Cu/Sn/Co couple, Cu can diffuse through the pure Sn solder, and the (Cu, Co)6Sn5 phase is formed at the Co side. The rate of consumption of Co decreases in the presence of Cu. Adding 0.04 wt.% Co to the pure Sn solder blocks diffusion of Cu; the (Cu, Co)6Sn5 phase at the Co side is not observed, and the rate of Co consumption is increased. In the Co/Sn/Ni couple, no noticeable Co and Ni diffusion is observed. When 0.04 wt.% Co is added, the ternary (Ni, Co)Sn4 phase is formed at the Ni side. These results indicate Co is an effective barrier to diffusion of Cu which can be used in flip chip packaging of Cu/low-k chips.