Electromigration (EM) in solder joints under high current density has become a critical reliability issue for the future high density microelectronic packaging. A practical method of atomic density integral (ADI) for predicting solder bump electromigration reliability is proposed in this paper by considering the driving forces of electron wind force, stress gradients, temperature gradients, as well as atomic density gradient. The electromigration simulation is performed on FCBGA package based on ADI method, and the simulation results for void generation and time to failure (TTF) have a reasonably good correlation with the testing results. Orthogonal experimental design has been used to evaluate the effect of design parameter on TTF of electromigration. Based on this study, some practical recommendations are made to optimize the package design and improve the solder bump electromigration reliability.