Phase equlibria studies of the Sn-Sb-Ni system at 270°C

The isothermal section of the Sn-Sb-Ni ternary system at 270°C is experimentally determined in this study. Sn-Sb and Sn-Sb-based alloys are viable high-temperature Pb-free solders, and Ni is the most frequently encountered surface finish in microelectronic industry. Sn-Sb/Ni is an important contact in using high temperature solders. Thus, phase equilibria information of the Sn-Sb-Ni ternary system is essential to the development of high-temperature Pb-free solders. 270°C is approximately the reflow temperature of the Sn-Sb solders. It is found that a Sn-Sb-Ni ternary phase, Ni(Sn_1-x, Sb_x)₃ (τ), exists at 270°C, where x=0.5-0.76. Based on the XRD structural determination, the τ phase is with a body-center-cubic (bcc) CoSb₃ crystal structure. The liquid phase has 14at%Sb and negligible Ni solubility, and the Rhombohedral-A7 Sb phase has 15at%Sn and negligible Ni solubility. The maximum Sb solubility in the Ni₃Sn₄ phase is 6.2at%. Six three-phase, 13 two-phase, and 10 single-phase region regions are determined. The six three-phase regions are liquid-Ni₃Sn₄-τ, liquid-Sn₃Sb₂-τ, Sn₃Sb₂-SnSb-τ, SnSb-Sb-τ, Sb-T-NiSb₂, and α-Ni₇Sb₃-β. The 13 two-phase regions are liquid-Ni₃Sn₄, liquid-τ, liquid-Sn₃Sb₂, Sn₃Sb₂-τ, SnSb-τ, Sn₃Sb₂-SnSb, SnSb-Sb, Sb-τ, Sb-NiSb₂, α-β, α-Ni₇Sb₃, β-Ni₇Sb₃, and β-Ni₃Sn₄.