Effect of pad shape on electromigration in solder bump joints

In this study, the effect of pad shape on current density and temperature distributions in solder joints has been investigated by three dimensional thermo-electrical finite element analysis. The simulation results show that square, hexagonal, octagonal and rounded pads with the same thickness/volume generate different current density and temperature distributions. The maximum current densities in solder bumps are 2.81×10⁴, 2.62×10⁴, 2.60×10⁴ and 2.66×10⁴ A/cm² respectively, while the maximum temperatures are 183.3, 181.5, 181.2 and 182.2°C respectively. Solder joints with octagonal pads generate the smallest current density and temperature, indicating that this geometry has the best electromigration reliability. The results indicate that electromigration reliability can be improved by changing pad shape, without enlarging joint size. Pad shape design is a promising solder joint structure design method for enhancement of electromigration reliability in line with the miniaturization trends of future electronic products. Better design of the pad structure should help alleviate the electromigration reliability problem.