Cross-interaction effect in the Ni/Sn/Cu solder joints

Abstract

The mutual interaction between Sn/Ni and Sn/Cu interfacial reactions in a Ni/Sn/Cu sandwich solder joint structure has been discussed in this present work. The major interfacial reaction product on the Sn/Cu interface was Cu6Sn5 phase, while on the Sn/Ni interface, a ternary (Cu,Ni)6Sn5 compound layer was formed, instead of the typical Ni-Sn compound phase. On the other hand, an asymmetrical solder microstructure was observed in the Ni/Sn/Cu solder joint. The asymmetrical solder microstructure resulted from the Cu concentration gradient along the Ni/Sn/Cu solder joint. Mechanical tensile tests showed that the mechanical property of the Ni/Sn/Cu solder joint is highly correlated with the asymmetrical solder microstructure.