Stress And Strain Analysis And Optimization Of Large Size PBGA Solder Joint With Underfill Under Combined Loading

Compared with QFP,CSP and other packaging devices,large-size PBGA has the advantages of more I / O ports,good electrical performance and good thermal matching performance.Therefore,it is widely used in the field of high-speed input / output computing.Due to its large size,large weight,complex assembly process and high use frequency,largesize PBGA equipment is vulnerable to the simultaneous action of bending,torsion and temperature impact,resulting in the failure of large-size PBGA interconnection solder joints.The reliability of large-size PBGA interconnection solder joints is usually improved by filling glue at the bottom of large-size PBGA devices.The solder joint of underfill large-size PBGA will still fail under the combined loading of temperature cycle,bending and torsion.Therefore,this paper studies the stress and strain of underfill large-size PBGA Solder Joint under the combined loading of temperature cycle,bending and torsion(hereinafter referred to as composite loading).Firstly,the sub model technology is used to model and simulate the large-size PBGA filled with rubber.Under the composite loading,the change law of solder joint stress strain is analyzed.The size of the solder joint stress strain at composite loading and single loading is compared.And the influence of underfill on the stress and strain of solder joints under combined loading is compared and analyzed.The influence of solder joint structure parameters on solder joint stress and strain is studied by single factor method,and the significance of solder joint structure parameters on solder joint stress of underfill PBGA is studied by orthogonal analysis method.The results show that the stress and strain of largesize PBGA Solder Joints filled with primer increase periodically;Under high temperature combined loading,the strain and stress of solder joint are large,while under low temperature combined loading,the strain and stress of solder joint are small,and the stress of solder joint is the largest at the beginning of low temperature insulation.The stress and strain of solder joints during composite loading are greater than those during single loading.During composite loading,the stress and strain of underfill PBGA solder joint is less than that of underfill PBGA Solder joint.The maximum stress-strain of solder joint is negatively correlated with solder joint height and pad diameter,and positively correlated with solder joint diameter.At 90% confidence level,pad diameter,solder joint diameter and height have a significant effect on the maximum stress.The order of influence size is: solder joint diameter > pad diameter > solder joint height.Secondly,the response surface method is used to design the structural parameters of the solder joint,and the simulation analysis results are used to fit the regression equation,The regression equation is optimized based on genetic algorithm,particle swarm optimization algorithm and differential evolution algorithm,and the optimized structural parameters of large-size PBGA Solder Joints filled with primer are obtained,which are verified by simulation analysis.The results show that using three optimization algorithms to optimize the solder joint structure parameters can improve the solder joint reliability of underfill largesize PBGA.The order of optimization effect is: genetic algorithm > differential evolution algorithm > particle swarm optimization algorithm.Thirdly,based on the BP neural network with a quantitative term,70 combinations of welded joint patterns are selected as training samples to establish a BP neural network prediction model.The stress prediction of large-size PBGA Solder Joint filled with primer under compound loading is realized.The neural network is tested by 10 groups of different solder joint structure parameters.The average error between the predicted value and the simulation value is 1.47%,which can better realize the stress prediction of large-size PBGA filled with primer under combined loading.Finally,the strain measurement platform of temperature cycle bending torsion composite loading is built to complete the strain measurement under composite loading.The error between the simulation value and the experimental value is less than 20%.Experiments prove the reliability of the simulation...