Interfacial reactions in Ag-Sn/Cu couples

Interfacial reactions between Sn-3.5 wt.%Ag, Sn-25 wt.%Ag, and Sn-74 wt.%Ag alloys with Cu substrate at 240°C and 450°C have been studied here by examining the reaction couples. It is found that Sn is the fastest diffusion species among the three elements during the reaction, while Ag is the slowest. The reaction path is liquid/η/ɛ1/Cu for the Sn-3.5 wt.%Ag/Cu couples reacted at 240°C. The paths are liquid/ɛ1/δ/Cu, liquid/ɛ1/δ/Cu, ɛ2/ζ/ɛ1/δ/Cu, for the Sn-3.5 wt.%Ag/Cu, Sn-25 wt.%Ag/Cu, and Sn-74 wt.%Ag/Cu couples at 450°C, respectively. These reaction paths are in agreement with the isothermal sections of the Ag-Sn-Cu ternary system at 240°C and 450°C. The isothermal sections are proposed based on the limited ternary phase equilibria data and the phase diagrams of its three constituent binary systems, Ag-Sn, Cu-Sn, and Ag-Cu.

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