Heterogeneous nucleation of βSn on NiSn4, PdSn4 and PtSn4

During Pb-free soldering, beta Sn often requires a high nucleation undercooling and there is an ongoing effort to develop nucleation catalysts. It is shown here that NiSn4, PdSn4 and PtSn4 are heterogeneous nucleants for beta Sn, reducing the nucleation undercooling to similar to 4 K when these intermetallics are present either in the bulk solder or as the interfacial layer. Nucleation catalysis occurs by beta Sn nucleating on the (0 0 8) facet of XSn4 crystals with an orientation relationship (OR) (1 0 0)Sn vertical bar vertical bar(0 0 8)XSn4 and [0 0 1]Sn vertical bar vertical bar[1 0 0]XSn4 where there is a planar lattice match of similar to 5%. This OR is also the origin of well-aligned lamellar beta Sn-XSn4 eutectic morphologies, even though the eutectics contain less than 2 vol.% of faceted NiSn4, PdSn4 or PtSn4. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.