Effect of pad geometry on current density and temperature distributions in solder bump joints

Three-dimensional thermo-electrical finite element analyses were conducted to simulate the current density and temperature distributions in solder bump joints with different pad geometries. The effects of pad thickness, diameter and shape on current density and temperate distributions were investigated respectively. It was found that pads with larger thickness or/and diameter could reduce current density and temperature in solder bump significantly. Pad shapes affected the current density and temperature distributions in solder bumps. The relatively low current density and temperature didn't occur in the bump joint with traditional rounded pad but occurred in bump joints with octagonal and nonagonal pads respectively. Therefore, optimized pad geometry may be designed to alleviate the current crowding effect and reduce the bump temperature, and therefore delay electromigration failure and increase the mean-time-to-failure.