Wetting kinetics of Sn-Pb eutectic solder on Cu and Cu-Sn intermetallics substrates

The wetting kinetics of the eutectic 63Sn-37Pb solder on Cu and Cu-Sn intermetallic compound (IMC) substrates were investigated. The results show that the spreading feature of 63Sn-37Pb solder on the Cu substrate changes with the exhaustion of element Sn as the Cu-Sn interfacial reaction goes on. In the initial stage, the spreading fits the simple liquid flow rule well, while with decreasing Sn, it comes into the typical reactive spreading character stage. The first sub-stage follows a model involving a local chemical reaction controlled wetting with the stable triple line moving rate under the condition of sufficient Sn supply. The second sub-stage shows a wetting behavior that follows a model of diffusion-controlled reactive spreading with the lacking supply of Sn. The spread of eutectic 63Sn-37Pb solder on Cu-Sn intermetallic compound substrates is very well, much better than its spread on Cu substrate.