Study on interfacial behavior and shear strength of lead-free micro-interconnect bump after SnPb reballing

The metallurgical structure and mechanical shear performance of replated solder bumps were studied. Firstly, the original lead-free interconnect bumps were removed by melt method and the SnPb solder bumps were soldered on the original soldering interface. Then the cross sections of replated bumps were obtained by polishing and the metallurgical structure and the composition of intermetallic layer at the soldering interface were analyzed by SEM&EDS. Secondly, the aging behavior of metallurgical structure of replated bumps was studied further. Finally, the dage4000 was employed and the shear tests were performed respectively on the solder bumps before and after replating. The results showed that the jagged nickel coating formed during the lead conversion process increased the contact areas between nickel coating and IMC layer, and the aging test of 85°C promoted the enhanced growth of IMC layer and even diffusion of solder grain, all of these playing the role of increasing mechanical strength of solder balls. The solder balls after lead conversion represented good shear strength, which proved that the lead free devices after lead conversion used in the high reliability electronic products were feasible.