Thermodynamic reassessment of Au–Ni–Sn ternary system

For having a better understanding on the formation and evolution of metal bonding interconnection microstructures the Au–Ni–Sn ternary system was reassessed on the basis of experimental results and the recently reported thermodynamical description for Au–Sn and Ni–Sn systems. In this paper, the thermodynamic parameters of Ni3Sn4 phase were modified in order to achieve a better agreement with experimentally determined phase boundaries. Further, a self-consistent set of thermodynamic parameters for the Au–Ni–Sn system were obtained, which were able to reproduce most of the available experimental data. The Ni|80Au20Sn (wt%) diffusion couples were annealed at 320 °C for 10,000 s and at 150 °C for 2500 h. The microstructures of these samples were studied with SEM+EDS technique. The reaction interface between Ni and near eutectic AuSn alloy consisted of Ni3Sn/(Ni, Au)3Sn2/AuSn/Au5Sn layers. This experimentally observed diffusion path of Ni against Au–20 wt% Sn solder at 150 °C was rationalized on the basis of the thermodynamically calculated isothermal section.