Effect of current density and geometry structure on Pb-free solder joints electromigration

Pb-free solders will replace traditional Sn-Pb solders to correspond with the green-packaging strategy. In this paper, a 2D model was presented to study the electromigration (EM) in Pb-free solder joints (Sn-Ag-Cu). Some geometry patterns of Cu thin films were designed and interconnected with Pb-free solder joints. The current density distribution in the special geometry pattern interconnect was analyzed with ANASYS. And then the testing data were obtained to compare with the simulation results. Numerical simulation showed that current density crowding occurred because of the interconnect geometry changes, which resulted in inhomogeneous drift of metal atoms. For a given geometry Pb-free interconnect, it was found that voids nucleated at the IMC interface where current density was crowding excessively and propagated along the current-density gradient direction. In the meantime, some hillocks were observed at the IMC interface of the anode. In addition, IMCs dissolved at the cathode or formed at the anode, of those whose boundary migrated in the EM process. Those phenomena were fully accorded with the prediction from simulation results. Finally, EM driving forces were applied to explain these phenomena.