The formation of nano-Ag3Sn particles on the intermetallic compounds during wetting reaction

The morphologies of the intermetallic compounds (IMC) forming during wetting reaction between molten Sn-3.5Ag, Sn-3.5Ag-0.7Cu lead free solder alloys and pure Cu and Ni substrate were investigated. It is quite interesting that nano-size Ag3Sn particles were found on the IMC surface. It seems that the formation of Ag3Sn particles takes place in the solidification process. The existence of these particles would decrease the interfacial energy and hamper the growth of the IMC layer. Adsorption theory is used to explain the formation of these particles and their effect on the surface energy of the IMC.