Use of thermodynamic data to calculate surface tension and viscosity of Sn-based soldering alloy systems

A thermodynamic database for the Pb-free soldering alloy systems, which include Sn, Ag, Cu, Bi, and In, has been made using the CALPHAD method. The resulting thermodynamic properties of the Sn-based binary alloy systems were used to determine the surface tensions and viscosities. The surface tensions were calculated using Butler’s monolayer model and the viscosities by Hirai’s and Seetharaman’s models. Butler’s model was also used to determine the surface active element. The results for binary systems were extended to the Sn-based ternary systems (Sn-Ag-Cu, Sn-Ag-Bi). The surface tensions of commercial eutectic Sn-Pb and Sn-Pb-Ag solder alloys were measured by the sessile drop method. The measured values and other researchers’ results were compared with the calculated data.