Effect of rare earth addition on shear strength of SnAgCu lead-free solder joints

In the present study, the effect of adding trace amount of rare earth (RE) on the shear strength of Sn3.8Ag0.7Cu lead-free solder joints has been investigated. The shear strength of the solder joints as-reflowed and after aging at 150 °C for 168 and 336 h was measured at a constant loading rate of 0.3 mm/min and room temperature. The investigation indicates that the shear strength of Sn3.8Ag0.7Cu0.1RE solder joints is lower than that of Sn3.8Ag0.7Cu solder joints. The shear strength of both Sn3.8Ag0.7Cu solder joints and Sn3.8Ag0.7CuRE solder joints was reduced after aging at elevated temperature. However, the shear strength reduction rate of the Sn3.8Ag0.7Cu solder joints was much faster than that of Sn3.8Ag0.7CuRE solder joints. Moreover, the fracture surfaces were examined by scanning electron microscopy (SEM) and the thickness of intermetallic compounds layer (IML) in the solder joints that join Cu substrate was measured. The results indicated that the addition of rare earth elements suppresses the growth of the thickness of intermetallic compounds layer.