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Nowadays the issues about reliability of IC caused by electromigration (EM) become very important. In this paper, a 3D model is presented to simulate the distribution of current density in lead-free flip chip bump interconnect. By the simulation, the effect of current crowding on electromigration in lead-free flip chip bump interconnect is studied. The simulation results show that when high current flows into and out of solder bump, current crowding occurs and large joule heat is generated. Through the analysis of experimental results, it can be found that the current crowding accelerates the electromigration in lead-free flip chip bump interconnect combined with joule heat. The extent of electromigration where the electron flow enters the under bump metallization (UBM) is more severe than other places in the cathode of the lead-free solder bump.