Study On Microscale Mechanical Behavior Of Electronic Packaging Sn58Bi Lead-free Solder Based On Nanoindentation Test And Finite Element Simulation

Electronic packaging is the foundation of microelectronics manufacturing,and solder joints are one of the weakest parts in electronic packaging systems.The solder joints in electronic packaging are formed by soldering,and the mechanical behavior of the solder is one of the important factors that affect the reliability of solder joints.Tin-lead(SnPb)solder has been widely used in the electronics industry due to its excellent mechanical properties.However,in recent years,because lead in waste electronic products endangers biological health and pollutes the environment,many industrial countries have successively banned the use of lead-containing materials in electronic products in the form of legislation.At present,in the electronics industry,lead-free solder has basically replaced Sn Pb solder.Among the lead-free solders,Sn58Bi lead-free solder has potential prospects in low-temperature brazing due to its low melting point and good mechanical properties.For a long time,the study on Sn58Bi lead-free solder has mainly focused on the macroscale mechanical properties of materials or solder joint samples.However,the size of the solder joints of electronic packaging has reached the micron-level.Due to the effect of the size effect,the macroscale mechanical performance parameters cannot well characterize the microscale mechanical behavior of the materials or phases in the micro solder joints.At present,study on the microscale mechanical behavior of Sn58Bi lead-free solder is lacking.In this study,based on the combination of nanoindentation test and finite element simulation,the microscale mechanical performance parameters and stress-strain relationship function expressions(Constitutive equation)of Sn-rich and Bi-rich phases in Sn58Bi lead-free solder and its microstructure in electronic packaging were studied.Firstly,according to the SnBi binary alloy phase diagram,eutectic Sn58Bi alloy and solid solution alloy with the same composition of Sn-rich phase and Bi-rich phase as its eutectic structure were prepared.After the nanoindentation test,the elastic modulus E and hardness H of Sn58Bi,Sn-rich phase,and Bi-rich phase were obtained,and their load-displacement curves were recorded.Secondly,according to the reverse analysis theory,the results of the nanoindentation test are assigned to the finite element model,and the finite element software ANSYS is used to perform reverse analysis on the loading stage of the load-displacement curve obtained by the nanoindentation test.by comparing the test loads-displacement curve and simulated load-displacement curve to determine the characteristic stress and characteristic strain of the tested material.Then the strain strengthening index of the tested material through the dimensional function was determined.By substituting the characteristic stress,characteristic strain,strain strengthening index and elastic modulus into power exponential model,the yield strength of the tested material was determined.Lastly,and the expression of the stress-strain relationship function of the tested material is determined.Finally,Sn58Bi and Sn-rich phase alloys were prepared into canine bone samples specimens that meet the tensile test requirements,and Sn58Bi and Sn-rich phase alloys canine bone samples were subjected to tensile test to obtain yield strength.Comparing the yield strength obtained from the reverse analysis and the yield strength obtained from the tensile test,it is found that there is not much difference between tensile test and reverse analysis,which verifies the accuracy of the expression of the corresponding stress-strain relationship function of Sn58Bi and Sn-rich phase.