Stress analysis and optimization of POP stacked solder joints under thermal cyclic load

The finite element model of packaging on packaging(POP) stacked solder joints was established, and the stress distribution state and thermal fatigue life of the solder joints under thermal cyclic load were analyzed based on the ANAND constitutive equation. The significance of the influence of the structural parameters of the POP package on the thermal stress of the solder joints was analyzed based on the sensitivity method. The regression equation of the thermal stress of the POP stacked solder joints and the structural parameters was established based on the response surface method, and the structural parameters were optimized by combining the particle swarm algorithm. The results show that the stress is highest at the contact between the solder joint and the copper solder disc, which is the location of the crack initiation. The upper and lower solder joint heights have a significant effect on the thermal stresses in POP stacked joints. The optimal combination of structural parameter levels is 0.35 mm for the upper solder joint height, 0.28 mm for the lower solder joint height and 0.26 mm for the middle PCB thickness, which reduces the maximum thermal stress of the upper and lower solder joints by 0.816 and 1.271 MPa, respectively, and prolongs the thermal fatigue life of POP stacked joints.