Effect of RE element addition and processing parameters on the shear strength and interfacial IMCs of SAC solder joints

The reliability of SAC lead-free solder joints are believed to be greatly influenced by the interfacial intermetallic compounds (IMCs) between solders and substrates. Our previous works investigated the effects of minimal rare earth (RE) elements addition on the interfacial IMCs under different aging time. Experimental results showed that the appropriate RE content is 0.07wt% La in Sn-0.3Ag-0.7Cu (SAC0307). In this paper, the influences of reflow parameters and Ce addition on the IMCs of SAC0307-0.07La/Cu solder joints were studied. The morphologies of IMCs were characterized by metallographic microscope (OM) and scanning electron microscope (SEM). Besides, the shear strength of the solder joints was evaluated by the shear tests. In comparison purpose, all the solder balls were prepared under the same conditions. The results showed that the thicknesses of the IMCs increased following the linear law and the shear strength varied under the parabolic law with the increase of reflow time. Meanwhile, the shear strength of the solder joints increased almost linearly with the increase of the cooling rate. The main failure mode was ductile fracture when the shear speed was 0.05mm/s.