Abstract
Specimens with the Sn/Cu/Sn/Ni/Sn/Cu/Sn structure reacted at 200°C are prepared and examined. The Cu 6 Sn 5 and Cu 3 Sn phases are formed at the Sn/Cu interface, and the Cu 6 Sn 5 and Ni 3 Sn 4 phases at the Sn/Ni interface. The reaction path in the original Cu/Sn/Ni part of the specimen is Cu/Cu 3 Sn/Cu 6 Sn 5 /Sn/Cu 6 Sn 5 /Ni 3 Sn 4 /Ni. The peculiar phenomenon of the Cu 6 Sn 5 phase forming at both sides of the Sn phase is illustrated using the Sn-Cu-Ni phase diagram with a very wide compositional-homogeneity range of the Cu 6 Sn 5 phase. Interfacial reactions at 240°C between pure Sn and (Cu,Ni) alloys of various compositions are determined. The Cu 6 Sn 5 phase is formed when the Ni content is less than 30 wt.%, and the Ni 3 Sn 4 phase is formed when the Ni content is higher than 40 wt.%. When the Ni content is between 35 wt.% and 40 wt.%, both Cu 6 Sn 5 and Ni 3 Sn 4 phases are formed. It is also noticed that the formation of the Cu 3 Sn phase at the Sn/(Cu,Ni) interface is suppressed with more than 1wt.%Ni addition in the substrate.