Premelting behavior and interfacial reaction of the Sn/Cu and Sn/Ag soldering systems during the reflow process

The early interfacial reaction and premelting characteristics of the Sn/Cu and Sn/Ag soldering systems, and the formation and morphology transition of interfacial intermetallic compounds in the two systems during the reflow soldering process were investigated by using a differential scanning calorimeter. Results show that the initial interfacial eutectic reaction arising from atomic interdiffusion in solid-state Sn/Cu and Sn/Ag systems results in the premelting at each interface of the two systems at a temperature 4.9 and 10.6 °C respectively lower than the actual melting point of pure tin, and consequently both of the Sn/Cu and Sn/Ag soldering systems exhibit morphology change of the intermetallic compound (IMC) as the solder experiences a transition from solid-state to liquid-state in a very small temperature range. The change in the interfacial energy between the solid (or liquid) Sn-rich phase and IMC phase is the essential factor leading to the morphology transition of the interfacial IMC in the Sn/Cu and Sn/Ag soldering systems.