The interfacial reactions and bump shear properties of the electroplated Sn-37Pb (in wt.%) solder bumps with the Ni under bump metallization (UBM) were investigated as a function of the number of reflows. A continuous facetted Ni3Sn4 intermetallic compound (IMC) layer was formed at the interface between the solder bump and the Ni UBM during reflow. The thickness of the Ni3Sn4 IMC layer was 0.41 μm after 1 reflow, and then the thickness of the IMC layer increased with increasing the number of reflows. The shear properties of the bumps indicated the maximum values after 1 reflow, and then decreased with increasing the number of reflows. The fracture surfaces of the bumps showed ductile failure characteristics after 1 reflow, and then the fraction of the brittle fracture, induced by the IMC formed at the interface, increased with increasing the number of reflows.