Study of microstructure, growth orientations and shear performance of Cu/Sn-3.0Ag-0.5Cu/Cu solder joints by using thermal gradient bonding

In this study, the effects of the thermal gradient (TG) applied during the bonding process on the microstructure, grain orientations and shear properties of Cu/SAC305/Cu solder joints were investigated, and the magnitude of the TG was controlled by the thickness of the solder layer. The results indicated that the introduction of TG caused the asymmetric growth of intermetallic compounds (IMCs) and enabled the rapid generation of IMCs at the cold end. Cu6Sn5, as the main component of IMCs in Cu/Sn solder joints, developed a strongly preferred orientation in the (0001) ‖ RD direction. While for β-Sn grains, the preferred orientation was uncontrollable, which formed the preferred orientations of (010) ‖ TD, (031) ‖ RD and (114) ‖ RD at 20 um, 60 um and 100 um solder joints, respectively. In addition, the TG reduced the reliability of solder joints whose shear properties were lower than those of joints with isothermal bonding.