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

Abstract

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 800°C, 500°C, and 200°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 τ1 (Sn3Ni4Zn3) and τ2 (Sn4Ni4Zn2).