Interfacial reaction between Sn–3.0Ag–0.5Cu liquid solder and Ni–xZn novel UBM layers

This work aims to investigate the interfacial reaction under liquid reactions of Sn–3.0Ag–0.5Cu (SAC305) joints with Ni–xZn films by sputtering. The surface roughness and residual stress of the Ni–xZn film, which was regarded to an under bump metallization (UBM), were evaluated using atomic force microscope (AFM) and the curvature measurement. The X-ray diffractometry (XRD) was used to further identify microstructures. Detailed morphology of the interfacial reaction in SAC305/Ni–xZn joints was performed by a field-emission scanning electron microscope (FE-SEM) with low angle backscattered electron detector (LABE). It was demonstrated that the microstructure evolution and phase formation in the SAC305/Ni–7Zn and SAC305/Ni–20Zn joints varied from reflow time and Zn content in the UBM films. The influence of the Zn concentration in Ni–7Zn and Ni–20Zn films on the different interfacial reactions was discussed and proposed.