This study explored the effect of Ag as the substrate or alloying element of solders on the interfacial reaction in Sn-Zn soldering. Results show that instead of Ag-Sn compounds, ζ-AgZn and γ-Ag 5 Zn 8 form at the Sn-Zn/Ag interface. The addition of Ag in Sn-Zn solders leads to the precipitation of ε-AgZn 3 from the liquid solder on preformed interfacial intermetallics. The morphology of this additional AgZn 3 is closely related to the solidification process of Ag-Zn intermetallics and the under intermetallic layer.

The interfacial interaction between the Sn-8.55Zn-0.5Ag-0.5Ga-0.1Al solder and three kinds of metallized substrates (Cu, Cu/Au, and Cu/Ni-P/Au) does not form the Cu-Sn intermetallic compound (IMC). Continuous Cu-Zn and discontinuous Ag-Zn interfacial IMC layers formed between the Cu and Sn-Zn-Ag-GaAl solder, while Cu-Zn and Au-Al-Zn IMCs formed on the Cu/Au substrate. Only the Au-Al-Zn IMC formed at the interface when the electroless Ni-P deposit was the diffusion barrier between Cu and the Au surface layer.