Interfacial reactions in the Sn-(Cu)/Ni, Sn-(Ni)/Cu, and Sn/(Cu,Ni) systems

Specimens with the Sn/Cu/Sn/Ni/Sn/Cu/Sn structure reacted at 200 degreesC are prepared and examined. The Cu6Sn5 and Cu3Sn phases are formed at the Sn/Cu interface, and the Cu6Sn5 and Ni3Sn4 phases at the Sn/Ni interface. The reaction path in the original Cu/Sn/Ni part of the specimen is Cu/Cu3Sn/Cu6Sn5/ Sn/Cu6Sn5/Ni3Sn4/Ni. The peculiar phenomenon of the Cu6Sn5 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 Cu6Sn5 phase. Interfacial reactions at 240 degreesC between pure Sn and (Cu,Ni) alloys of various compositions are determined. The Cu6Sn5 phase is formed when the Ni content is less than 30 wt.%, and the Ni3Sn4 phase is formed when the Ni content is higher than 40 wt.%. When the Ni content is between 35 wt.% and 40 wt.%, both Cu6Sn5 and Ni3Sn4 phases are formed. It is also noticed that the formation of the Cu3Sn phase at the Sn/(Cu,Ni) interface is suppressed with more than 1wt.%Ni addition in the substrate.