Microstructural evolution of ε-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 epsilon-AgZn3 and eta-Zn phases in Sn-8.5Zn-0.5Ag-0.01Al-0.1Ga solder (5-e alloy) during isothermal aging treatment at 150 degrees 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 (eta-Zn), the combination of epsilon-AgZn3 with precipitated Zn-rich became a diffusion couple. The epsilon-AgZn3 compound shrinks apparently upon heat exposure. Furthermore, at the interface of this diffusion couple, it seems to exit a phase transition between epsilon-AgZn3 IMC and eta-Zn phase. This phase transition mechanism will be discussed in this paper. (C) 2008 Elsevier B.V. All rights reserved.