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

The measured undercooling of pure Sn was about 30 degrees C due to the difficulty of nucleating a solid beta-Sn phase from a liquid phase. To promote the heterogeneous nucleation of beta-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 beta-Sn phases in Sn-rich solders. Calculations of the density functional theory indicate that the interfacial energy between beta-Sn and Zn was relatively low. Minor alloying elements with hcp crystals are expected to provide more favorable heterogeneous nucleation sites for beta-Sn phases.