Liquid-state interfacial reactions in Sn–Zn/Pd couples and phase equilibria of the Sn–Zn–Pd system at 260 °C

• Liquid-state Sn–Zn/Pd interfacial reactions were examined.
• IMC phase changed from Pd2Zn9 to PdSn4 with Zn content from 2 wt.% to 1 wt.%.
• The PdSn4 growth was greatly suppressed with only 0.5 wt.% Zn addition.
• A drastic microstructural evolution occurred in the Sn–1.5 wt.%Zn/Pd reaction.
• Isothermal section of the Sn–Zn–Pd ternary system at 260 °C was determined.

This study investigated the effects of Zn contents on the reaction products and microstructural evolution in the liquid/solid Sn–Zn/Pd interfacial reactions at 260 °C. A uniform Pd2Zn9 layer was formed at the Sn–9 wt.%Zn/Pd interface. The reaction phase transited from Pd2Zn9 to PdSn4 when the Zn content decreased from 2 wt.% to 1 wt.%. The most striking feature is that the PdSn4 growth was greatly suppressed with only 0.5 wt.% Zn addition in solders. Additionally, a drastic microstructural evolution was observed in the Sn–1.5 wt.%Zn/Pd reaction. The Pd2Zn9 layer was initially formed and then it was detached from the interface due to the decrease in the Zn content. Subsequently, the dominant phase changed to the PdSn4 phase. Furthermore, a partial isothermal section in the Sn–Zn–Pd ternary system (less than 20 at.%Pd) at 260 °C was experimentally determined. The liquid apex of the liquid + PdSn4 + Pd2Zn9 tie-triangle was located at Sn–2.7 at.%Zn–1.0 at.%Pd. The phase transition from Pd2Zn9 to PdSn4 in the interfacial reactions was in good agreement with the phase equilibria relationship.