Phase Equilibria in the Sn-Ni-Zn Ternary System: Isothermal Sections at 200A°C, 500A°C, and 800A°C

In the electronic packaging field, the Sn-Zn alloy system has been recommended as a high-temperature Pb-free solder. There is a need for thermodynamic data on the Sn-Ni-Zn ternary system. Such data would serve as a basis for understanding the interfacial reaction between Sn-Zn high-temperature solder and Ni substrates and for thermodynamically evaluating the proper composition level of Ni and Zn in Sn-based solder. This study has investigated the phase equilibria of the Sn-Ni-Zn ternary system at 800A degrees C, 500A degrees C, and 200A degrees C (for Ni composition of less than 60 at.%). Scanning electron microscopy (SEM), x-ray diffraction (XRD), and electron probe microanalysis (EPMA) were used to identify the equilibrium phases. On the basis of the experimental data and thermodynamic parameters, the isothermal sections of the Sn-Ni-Zn ternary system have been described, considering the ternary solubility in the binary phases and newfound ternary phases tau 1 (Sn(3)Ni(4)Zn(3)) and tau 2 (Sn(4)Ni(4)Zn(2)).