Thermodynamic Assessment of the Ni-Bi Binary System and Phase Equilibria of the Sn-Bi-Ni Ternary System

As a basis to understand the interfacial reaction between the Sn-Bi solder and the Ni substrate in electronic packaging, thermodynamic calculations of phase equilibria have been carried out on the binary Ni-Bi system. The Gibbs free energy of the NiBi phase has been approximated, using a three-sublattice model, and thermodynamic parameters have been evaluated, using available experimental information on phase boundaries and other related thermodynamic properties. The calculated phase diagram and thermodynamic quantities of the Ni-Bi binary system showed good agreement with the experimental data. The Sn-Bi-Ni ternary system was calculated using the thermodynamic parameters of the Sn-Bi, Sn-Ni, and Ni-Bi binary systems, and it was compared with experimental measurements.