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 wetting interaction of Sn-(7.1-9)Zn-(0-3)Ag solders with Cu was investigated from 230°C to 300°C. The wetting time, wetting forces, and activation energy of the wetting reaction were studied. The wetting time decreases with increasing temperature and increases with Ag content. The wetting force exhibits a disproportional correlation to temperature rise, while no trend was observed with respect to Ag content. The wetting behavior was ascribed to the interaction between Cu and Zn. The AgZn 3 compound was formed at the interface when the solder contains 0.3% Ag and above, while it was formed within the bulk solder at 2% Ag and above.

The microstructure and thermal behavior of the Sn-Zn-Ag solder were investigated for 8.73-9% Zn and 0-3.0% Ag. The scanning electron microscopy (SEM) analysis shows the Ag-Zn compound when the solder contains 0.1% Ag. X-ray diffraction (XRD) analysis results indicate that Ag 5 Zn 8 and AgZn 3 become prominent when the Ag content is 0.3% and above. Meanwhile, the Zn-rich phase is refined, and the Zn orientations gradually diminish upon increase in Ag content. The morphology of the Ag-Zn compound varies from nodular to dendrite structure when the Ag content increases. The growth of the Ag-Zn compounds is accompanied by the diminishing of the eutectic structure of the Sn-9Zn solder. Differential scanning calorimetry (DSC) investigation reveals that the solidus temperature of these solders exists at around 198°C. A single, sharp exothermic peak was found for the solders with Ag content less than 0.5%. Liquidus temperatures were identified with the DSC analysis to vary from 206°C to 215°C when the Ag content ranges from 1.0% to 3.0%