Effects of Minor Amounts of Zn on the Sn-Zn/Ni Interfacial Reactions and Phase Equilibria of the Ternary Sn-Zn-Ni System at 250°C

Abstract

This study investigated the effects of minor Zn additions (less than 1 wt.%) to pure Sn on the phase formation and microstructural evolution at the interfaces between Ni and Sn-Zn solders. When the Zn content was less than 0.3 wt.%, the reaction product was Ni 3 Sn 4 , which had no Zn solubility. By contrast, for reactions with more than 0.4 wt.% Zn, one high-Zn-containing phase (about Sn-35 at.%Ni-20 at.%Zn) was formed, which was proven to be a ternary intermetallic compound, the s-phase. In addition to composition analysis, x-ray diffraction (XRD) analysis revealed that the crystallographic structure of the s-phase was different from that of Ni 3 Sn 4 . Furthermore, a partial isothermal section in the Sn-Zn-Ni ternary system (less than 40 at.% Ni) at 250°C was experimentally determined to contain 12 different Sn-Zn-Ni alloys. Three three-phase regions were identified: Ni 3 Sn 4 + s + liquid, Ni 5 Zn 21 + s + liquid, and Ni 5 Zn 21 + Zn + liquid. The equilibrium phase boundaries for liquid separately with Ni 5 Zn 21 , s, and Ni 3 Sn 4 were highly consistent with the Zn concentrations where the phase transitions occurred in the interfacial reactions.

Liquid-state interfacial reactions in Sn–Zn/Pd couples and phase equilibria of the Sn–Zn–Pd system at 260 °C

“…When decreasing to 2 wt.%Zn, the dominant phase changed to the ternary t IMC (Sne35 at.%Nie20 at.%Zn). With less than 0.3 wt.%Zn, the reaction product was the Ni 3 Sn 4 [17,18]. In addition, the growth kinetics of the Ni 5 Zn 21 phase was also systematically investigated in liquid-state and solid-state reactions [19].…”