Abstract: Finite element analysis was used to investigate the stress distribution of PBGA soldered joints with different arrangement models, and the constitutive relationship of Sn3.0Ag0.5Cu lead-free solder was described by Anand model.The results indicate that the positions of critical soldered joints are determined by the chip corner.The maximum stress of PBGA121 soldered joints increases when chip size increases, while the maximum stress of PBGA81 soldered joints decreases first and then increases.Based on the modified Manson-Coffin model by Engelmaier, the fatigue lives of critical soldered joints conditions corresponding to four different chip sizes were predicted, and it is found that the size of Silicon chip has a significant effect on the fatigue life of soldered joints.