Development of thermodynamic database for micro-soldering alloys

Recent progress on the database of calculated phase diagrams in micro-soldering alloy systems, which consist of Pb, Bi, Sn, Sb, Cu, Ag, In and Zn, is presented. Experimental determination of phase equilibria was conducted in several binary, ternary and quaternary systems by DSC, EDX and X-ray diffraction techniques. Based on these experiments, as well as on previous data on phase diagrams and thermo-chemical properties such as activity, heat of mixing and enthalpy of formation, the various thermodynamic parameters for describing the Gibbs energies of the different constituent phases were optimized and evaluated by the CALPHAD (calculation of phase diagrams) method. The database provides key information on liquidus and solidus surfaces, isothermal and vertical section diagrams, and mole fractions of the phase constitutions of multi-component soldering alloys. Thermodynamic properties of the surface tension and viscosity of the liquid phase can also be predicted. Moreover, a nonequilibrium solidification process using the Scheil model was simulated. Several phase diagrams of Pb-bearing and Pb-free solders are presented. The database is expected to be a powerful tool and an indispensable resource for the development of new Pb-free solders.