The growth behavior of intermetallic compound layer of Sn-Ag-Cu/Cu interface during soldering

The melting properties of Sn-3.5Ag, Sn-3.5Ag-0.7Cu, Sn-3.5Ag-1.7Cu and Sn-0.5Ag-4Cu lead-free solder alloys and the growth behavior of the intermetallic compound (IMC) layer of these solders on a Cu substrate during soldering are investigated. The results indicate that the melting points of Sn-3.5Ag, Sn-3.5Ag-0.7Cu and Sn-3.5Ag-1.7Cu solders are quite similar with one eutectic peak, while Sn-0.5Ag-4Cu solder has two endothermal peaks according to β | Cu₆Sn₅ + Ag₃Sn → L and β + Cu₆Sn₅ → L reactions, respectively. With the increasing Cu content in Sn-3.5Ag, Sn-3.5Ag-0.7Cu and Sn-3.5Ag-1.7Cu solders, the IMC thickness decreases due to the decrease of the dissolution rate of the IMC. The IMC thickness of Sn-0.5Ag-4Cu is quite thin when the soldering time is short. However, with increasing soldering time, the thickness turns thick very soon, which is led by the precipitation effect of the Cu₆Sn₅ in the liquid solder.