Stress analysis and optimization of QFN solder joints under bending-torsion coupled conditions based on the SSA

A 3D finite element model of QFN (Quad Flat No-Lead Package) solder joints was established for stress–strain analysis under bending-torsion coupled loading. The accuracy of the finite element simulation was validated through bending-torsion coupled strain measurement experiments. The effects of pad length, pad width, solder joint standoff height, and PCB (Printed Circuit Board) thickness on bending-torsion coupled stress–strain behavior were analyzed using univariate and correlation analysis. To minimize stress, these parameters were optimized using the response surface-Sparrow Search Algorithm (SSA). Results show a weakly positive correlation for pad length, strong negative correlations for pad width and standoff height, and a strong positive correlation for PCB thickness. The optimal parameters – pad length 0.66 mm, pad width 0.25 mm, solder joint standoff height 0.09 mm, and PCB thickness 1.2 mm – reduced maximum stress by 10.8 MPa. The research findings provide theoretical guidance for reducing the bending-torsion coupled stress of QFN solder joints.