Abstract: In order to evaluate the reliability of PBGA soldered joints, an optimized method was proposed based on Taguchi design and numerical simulation, in which the Anand equation was used to describe the viscoplastic behavior of Sn3.0Ag0.5Cu solder, and the distribution of equivalent stress and strain in soldered joints under temperature cycle were studied respectively.Results indicate that the thermal fatigue life of soldered joints can be substantially improved by filling up the underfill between the PCB and substrate.The linear expansion coefficients of substrate, epoxy mold compound, underfill and PCB were considered as the controlling factors, and the linear expansion coefficient of the substrate and that of epoxy mold compound were deemed to the main influencing factors by Taguchi method.The optimized controlling factor combination can be decided as A3B3C3D3, and the verification test shows the maximum equivalent strain of the optimization scheme was decreased by 41.4%, and the ratio of signal to noise was increased by 4.61 dB.