Microstructural evolution of ɛ-AgZn3 and η-Zn phases in Sn-8.5Zn-0.5Ag-0.01Al-0.1Ga solder during aging treatment

This study investigated the microstructural evolution of ɛ-AgZn3 and η-Zn phases in Sn-8.5Zn-0.5Ag-0.01Al-0.1Ga solder (5-e alloy) during isothermal aging treatment at 150 °C. Zn element easily precipitates on the surface of AgZn3 intermetallic compounds (IMCs) and grows rapidly during aging. During aging, Ag dissolves in the precipitated Zn which forms the Zn-rich phase (η-Zn), the combination of ɛ-AgZn3 with precipitated Zn-rich became a diffusion couple. The ɛ-AgZn3 compound shrinks apparently upon heat exposure. Furthermore, at the interface of this diffusion couple, it seems to exit a phase transition between ɛ-AgZn3 IMC and η-Zn phase. This phase transition mechanism will be discussed in this paper.