Interfacial microstructure evolution and shear behavior of Au–12Ge/Ni solder joints during isothermal aging

Abstract

During isothermal aging, the interfacial microstructure evolution of Au–12Ge/Ni joints as well as its influence on the shear strength and the fracture behavior have been investigated. Results showed that there was a duplex layer of NiGe and Ni5Ge3 intermetallic compounds (IMCs) in the joints after soldering. The most obvious changes in morphology were the transformation from scallop type to planar type microstructure. EPMA data indicated that the growth of the total IMC layer was mainly attributed to the growth of Ni5Ge3 phase. Furthermore, it was found that the grain boundary diffusion was the dominant growth-controlling mechanism of overall IMC layer and the activation energy was 82.23 kJ/mol. In addition, the shear strength decreased continuously with extended aging time. The fracture of as-produced joint was at solder/IMCs interface, showing both ductile and brittle morphology. After the subsequent aging process, a thicker IMC layer was formed at the interface, leading to the movement of the fracture to IMCs region, a transformation of fracture to brittle morphology and a deterioration in shear strength.