Microstructure and its effect on mechanical behavior of Sn-Ag-Cu/Cu single crystal solder joints

To explore the microstructural evolution of Sn-3.0Ag-0.5Cu/Cu single crystal solder joints and its effect on mechanical properties, Sn-3.0Ag-0.5Cu/Cu single crystal solder joints welded at 260 degrees C for different reflux times were prepared. The results show that interfacial layers formed at various reflux times consist of Cu6Sn5 grains; with a prolonged reflux time, the interfacial compound layer becomes thicker and denser due to the growing-up of Cu6Sn5 grains. The ultimate tensile strength of welding joints starts to increase as the reflux time is above 30 s and reaches the maximum at 600 s. Yield strength largely increases compared to Cu single crystal; however, with prolonging time, there is no obvious change, except the case that yield strength increases at 600 s. The cracks formed during deformation primarily appear within the interfacial layer, which results from the strain mismatch at solder/compound layer/Cu interfaces along with the collision of slip bands in Cu substrate on the compound layer.