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.