Study Of Mechanical Response In BGA Packing Structure Under Thermal Cyclic Loading

With the rapid development of electronic industry,people have higher and higher requirements for information transmission energy of electronic devices.Electronic packaging is developing in the direction of miniaturization and high integration of components.In order to meet the new requirements of more and more dense solder joints in electronic packaging,ball grid array(BGA)emerges as the times require and becomes the mainstream packaging form.The statistical results show that for electronic packaging structures,solder joints and other interconnection structures are the most prone to failure in electronic devices,and temperature and temperature cycle are the main causes of solder joint damage and failure.Therefore,this paper takes BGA packaging circuit board as the research object,and carries out the research work on the solder joint damage and failure under the condition of temperature cyclic load.Solder joints are the weakness of the encapsulation structure,and the creep characteristics are obvious.In order to solve the problem of creep constitutive model characterization and parameter acquisition of solder joints,the uniaxial tension test of lead-tin solder is carried out in this paper.Uniaxial tension test of lead-tin solder is carried out in this paper.Uniaxial tension tests of lead-tin brazing at different temperatures and loading strain rates were carried out.All nine parameters of Anand creep constitutive model were identified by non-linear fitting of stress-strain data and simulated annealing optimization algorithm.The fitted curves are in agreement with the experimental curves,which proves that the fitted data are valid.This provides a basis for subsequent simulation analysis using the Anand constitutive model.Then,the deformation and thermal stress of BGA encapsulated structure under temperature-dependent load are analyzed and calculated by theoretical deduction and FEM simulation.The analysis results show that the difference of linear expansion coefficient of each connecting part is the main cause of thermal stress.Under asymmetric cyclic temperature load,the weld produces cumulative creep deformation,and the distortion at the four corners is the largest.After several cycles,the fatigue failture of solder joints occurs.The deduced calculation method is consistent with the finite element analysis result,which a technical means for damage analysis of encapsulated structures under temperature-dependent load.After that,Fortran subroutine was written to characterize the creep properties of solder joints by combining the two creep constitutive models Anand and Wiese.Several life evaluation models of encapsulated structures were summarized.Based on the failure characteristics analyzed in the previous section,creep-fatigue related life models were selected for life evaluation method for BGA encapsulated structures based on failure physics was established.The fatigue life of solder joints under temperature-dependent load for BGA printed circuit boards is predicted.Finally,in order to solve the problem of strain measurement in solder joints,the DVC method is used to measure the inelastic strain at the crack of solder joints,and the accuracy of simulation results is verified.Three-dimensional digital images of solder joints of printed circuit boards were obtained by temperature cycling test of printed circuit board samples,and all solder joints strains were calculated and analyzed.The results of the test are consistent with the rules and trends of the simulation results.All the solder joints are micro-characterized,the actual shape distribution and statistical results of the solder joint are analyzed,and the basis for further refined modeling and simulation.In this paper,the failure mode and damage mechanism of solder joints under temperature-dependent load are revealed by theoretical derivation and finite element analysis.Two constitutive models were introduced to describe the creep behavior of solder joints and material tests were carried out to obtain model parameters.Typical test samples were designed and temperature-cycle tests were carried out.The non-elastic strain inside the solder joints was mrasured by CT comnined with DVC method.The three-dimensional morphology of BGA-encapsulated solder joints was characterized and analyzed,which laid a foundation for fine modeling of solder joints based on image finite element.The analysis and measurement methods explored in this paper provide important technical means for damage assessment of encaosulated structures.