Morphological evolution induced by volume shrinkage in micro joints

In this study, sandwich structures of Ni/Sn/Ni was prepared by a general electroplating process. A high temperature storage test was conducted by isothermal aging at 180°C. Microstructure characterizations revealed that after 24 hours of heat treatment, the Sn solder consumed completely. Cross-sectional microstructure showed large voids was left among the IMC. The ratio of Voids is much beyond -11.3%, the theoretical volume shrinkage ratio induced by Ni/Sn interfacial reaction. In addition, the Ni
₃
Sn
₄
phase grew laterally and the ring-like morphology formed at the surface. We believe that surface diffusion contribute significantly in real micro joints and that such a microstructure would degrade its reliability.