Analysis and Optimization of Residual Stress after Reflow Soldering of BGA Lead Free Solder Joints

A finite element model of residual stress after reflow soldering of lead free BGA solder joints is established, and analyzed the residual stress after reflow soldering under the structure-thermal coupling conditions. The deterministic experiment is designed and completed based on the Hole drilling strain-gauge method. The significance and the order of the influence of solder joint height, solder joint diameter, pad diameter and solder joint pitch on the residual stress of solder joints are analyzed based on the sensitivity method. Setting the factors that have significant influence on residual stress are variable, and then the structural parameters of solder joints are optimized by response surface method and genetic algorithm. The results show that the deterministic experiment results verify the effectiveness of the simulation analysis results. The significant factors for the residual stress are the solder joint diameter, solder joint pitch and solder joint height when the confidence is 95%, and the order of sensitivity from large to small is solder joint diameter, solder joint diameter and solder joint height. The optimal structure parameter combination of the solder joint of the minimum residual stress after reflow soldering is that solder joint diameter of 0.55 mm, the solder joint height of 0.36 mm and the solder joint pitch of 1.07 mm.The simulation results of the solder joint show that the maximum residual stress decreased 0.998 MPa.The research results have certain guiding significance and reference value for reducing the residual stress after reflow soldering of BGA solder joints.