The growth and roughness evolution of intermetallic compounds of Sn–Ag–Cu/Cu interface during soldering reaction

Abstract The growth behavior and roughness evolution of intermetallic compounds (IMCs) layer between Sn–3.5Ag, Sn–3.5Ag–0.7Cu, Sn–3.5Ag–1.7Cu and Sn–0.5Ag–4Cu lead-free solder alloys and Cu substrate are investigated during soldering under 250 °C. With the increase of Cu content in Sn–3.5Ag, Sn–3.5Ag–0.7Cu and Sn–3.5Ag–1.7Cu solders, the IMC thickness increases due to the decrease of the dissolution rate of the IMCs. The IMC thickness of Sn–0.5Ag–4Cu is quite thinner in a short soldering time. However, with the increase of soldering time, the IMCs layer grows quickly due to the precipitation effect of the Cu 6 Sn 5 in the liquid solder. With the increase of soldering time, the roughness of all the IMC layers increases. The roughness of Sn–3.5Ag–0.7Cu and Sn–3.5Ag–1.7Cu interfaces is larger than that of Sn–3.5Ag while Sn–0.5Ag–4Cu/Cu interface has the smallest roughness value. It is believed that the small IMC roughness of Sn–3.5Ag/Cu interface is caused by the IMCs dissolution, and the large IMC/liquid solder interfacial energy maybe the reason for Sn–0.5Ag–4Cu/Cu interface obtaining the smallest IMC roughness.