Morphology and growth mechanisms of SAC305-xNi/pad joints intermetallic compounds

The formation and growth of intermetallic compounds (IMC) is a key factor to the reliability of soldering joints in modern electronic mounting and packaging industry. In this paper, by means of Olympus, scanning electron microscope (SEM) and Energy Dispersive X-ray (EDX) analysis methods, the morphology and growth mechanisms of IMCs between SAC305-xNi and Cu joint during soldering as well as aging were studied. Ni addition made IMC of SAC305/Cu joint turn into (Cu1-x, Nix)₆Sn₅ which appeared irregular island shape. The content of Ni in the IMC was different as the aged time prolonged. The average content of Ni in the SAC305-0.1Ni/Cu joint IMC which showed an increasing tend from the side near Cu to the bulk solder side was 5wt%. However, the two regions which average content of Ni in the SAC305/Ni joint IMC was respectively 17wt% and 7wt% showed a descending tend from the side near Ni to the bulk solder substrate side. It would force the type transformation to form (Ni, Cu)₃Sn₄ when the content of Ni was more than 22wt.% in the SAC305-0.1Ni/Ni joint IMC. The formation and evolution physics model of IMC was established by analysis of SAC305-x(Ni, Bi)/pad interfacial microstructure.