Stress-strain Analysis Of PBGA Stacked Solder Joints With Different Loads Based On Parametric Submodeling

The PBGA package is one of today’s mainstream packaging technologies due to its high packaging density,electrical performance and good thermal performance.A large number of studies have shown that the height of interconnecting solder joints in PBGA packages is one of the most important factors influencing the reliability of solder joints.By increasing the height of solder joints through the use of solder joint stacking,the stacked joint technology can reduce the shear stress of solder joints under temperature cycling due to thermal mismatch phenomenon,thus improving the reliability of solder joints.Stacked solder joint technology is a new type of interconnecting solder joint technology.In this paper,the stress-strain of PBGA stacked solder joints under different load loading is investigated,and the details and results are as follows:(1)Introducing the idea of structural optimality,based on the parametric sub-model method to establish a parametric equivalent overall model for PBGA stacked solder joints.The method is able to establish the overall model of PBGA stacked solder joints FEA with a more accurate and efficient alternative to the full-domain or local PBGA stacked solder joints FEA method.It improves the previous crude method of modeling equivalent solid solder balls by the equal volume principle and corrects the shortcomings of the previous cubic equal volume submodeling analysis method.This method can significantly reduce the number of cells in FEA,improve the flexibility of FEA modeling,and save computational time and computer resources.(2)Based on parametric sub-model modeling method,an equivalent overall model of PBGA stacked solder joints is established and finite element analysis is performed under temperature cyclic loading conditions.The results of the study show that the stress and strain distribution in the PBGA stacked solder joints is not uniform under the temperature cyclic loading conditions,and the edge area away from the center of the solder joint array is the danger area where the solder joints are prone to failure.Among the three solder joint structure parameters that affect the PBGA stacked solder joints thermal fatigue life of solder joints: solder ball diameter,solder joint height and pad diameter,the thermal fatigue life of stacked solder joints decreases with increasing solder ball diameter,increases with increasing solder joint height and increases with increasing pad diameter.The second-order reaction surface model of the structural parameters of the solder joint and the the average viscoplastic strain energy density increment of the solder joint is obtained using the reaction surface analysis method,and the model fits significantly and well.After optimization of the reaction surface model using genetic algorithm,the combination of solder joint structure parameters level with the highest thermal fatigue life of solder joints was obtained: solder ball diameter 0.70 mm,solder joint height 0.52 mm,and pad diameter0.62 mm.(3)This paper presents a finite element simulation of the stress-strain of a PBGA stacked solder joint under bending and torsional load loading conditions.The results showed that under bending load and torsional load loading conditions,the equivalent stress-strain distribution in the PBGA stacked solder joint array and inside is not uniform,and the edge area at the periphery of the solder joint array is the hazardous area with the largest stress-strain in the solder joint.The PBGA stacked solder joints structure parameters of solder ball diameter,solder joint height and pad diameter all have significant effects on the bending and torsional stress of solder joints,with the effect size of: solder joint height > solder ball diameter > pad diameter.When the ball diameter is 0.70 mm,the joint height 0.52 mm and the pad diameter 0.62 mm,the value of bending stress and torsional stress in the solder joint is the smallest.