Enhancement of heterogeneous nucleation of β-Sn phases in Sn-rich solders by adding minor alloying elements with hexagonal closed packed structures

Abstract

The measured undercooling of pure Sn was about 30 °C due to the difficulty of nucleating a solid β-Sn phase from a liquid phase. To promote the heterogeneous nucleation of β-Sn phases, the addition of impurity elements to the solders was suggested. Among the impurity elements, alloying elements with hexagonal closed packed (hcp) structures, such as Co, Zn, Ti, and Mg, were found effective to enhance heterogeneous nucleation of β-Sn phases in Sn-rich solders. Calculations of the density functional theory indicate that the interfacial energy between β-Sn and Zn was relatively low. Minor alloying elements with hcp crystals are expected to provide more favorable heterogeneous nucleation sites for β-Sn phases.