Interfacial reactions in the Sn-9Zn-(xCu)/Cu and Sn-9Zn-(xCu)/Ni couples

Sn-Zn-based alloys are promising low melting-point Pb-free solders, and it has been reported that their wetting properties and oxidation resistance can be improved with the addition of Cu. The interfacial reactions in the Sn-9 wt% Zn-xCu/Cu couples at 250 degrees C and Sn-9 wt% Zn-xCu/Ni at 280 degrees C were examined in this study. A thick gamma-Cu5Zn8 phase layer and a very thin beta '-CuZn phase layer were formed in both the Sn-9 wt% Zn/Cu and the Sn-9 wt% Zn-1 wt% Cu/Cu couples. The gamma-Ni5Zn21 phase layer was formed in both the Sn-9 wt% Zn/Ni and Sn-9 wt% Zn-1 wt% Cu/Ni couples. With longer reaction time, the delta-Ni3Sn4 phase were formed in the Sn-9 wt% Zn/Ni couple as well. In both the Cu and Ni couples, the Zn-containing gamma phases were uniform and planar and were the dominant reaction products. However, when the Cu content of the Sn-9 wt% Zn-xCu solders was 10 wt%, the interfacial reaction product becomes the eta-Cu6Sn5 phase in both the Cu and Ni couples.