M. Nagaoka 1, T. Morohoshi 2, H. Esaka 1 and K. Shinozuka 1
1 Department of Materials Science and Engineering, National Defense Academy
The amount of undercooling required for the nucleation of (β-Sn) in Sn-6.0 mass%Zn alloy was found to be extraordinarily small compared with other Sn-based alloys. One reason for this may be that the solute Zn is oxidized during the process to form ZnO, and this may assist the nucleation of (β-Sn). The disregistry between ZnO and (β-Sn) was analyzed. It was found that crystalline ZnO may be effective for nucleation of (β-Sn), since the disregistry is small. In order to test the nucleation effect of ZnO on β-Sn, dipping experiments were carried out. ZnO powder used in this study was analyzed by X-ray and found to be crystalline. Pure Sn and Sn-2 mass%Ag alloy were chosen as test metals and the undercooling for nucleation of (β-Sn), ΔT, was characterized. It was found that ΔT was large regardless of whether ZnO was dipped in the Sn alloy melt. This indicates that ZnO may not be effective for the nucleation of (β-Sn). Therefore, it can be concluded that low disregistry is a necessary condition but does not ensure nucleation.
lead-free solder, β-tin, undercooling, heterogeneous nucleation, wettability, disregistry
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