Abstract: The soldered joint reliability of 1.27mm pitch plastic ball grid array(PBGA) package was studied by Taguchi design experiment method under the thermal shock.The stencil thickness,the pad diameter and the chip weight were chosen as the three critical factors for the design of the PBGA test specimens by using a Taguchi orthogonal array.The thermal shock cycling test of PBGA test specimens was carried out.The range analysis and the variance analysis were performed to determine both the best combination of the process parameters and the most influential factors;the failure distribution of PBGA soldered joints was also characterized by using two-parameter Weibull distribution.The results show that the thickness of stencil has a significant effect on the reliability of the 1.27 mm pitch PBGA soldered joints.The optimal of process parameters are the stencil thickness of 0.15 mm,the pad diameter of 0.73 mm and the chip weight of 18.0547 g.The failure life of PBGA soldered joint follows the twoparameter Weibull distribution,whose shape parameter and scale parameter are 0.85 and 6254.88,respectively.