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

Abstract

Specimens with the Sn/Cu/Sn/Ni/Sn/Cu/Sn structure reacted at 200°C 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°C 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.