Research On Microscale Mechanical Behavior And Coupled Thermo-electrical Analysis Of Sn58Bi Solder Alloy In Electronic Packaging

The reliability of the micro-interconnect structure of electronic packaging often determines the service life of the entire electronic products and equipment.The damage of the micro-interconnect structure in the electronic packaging is usually caused by the failure of the solder joints.These micro solder joints will be invalidated by electric,heat and force fields during the service process.With the continuous development of high-density packaging technology,the size of solder joints has reached tens of microns,and the solder alloy matrix of solder joints has obvious microstructure inhomogeneity.The microstructure of the matrix has a significant impact on the mechanical properties of solder joints.However,most of the current researches focus on the macro-mechanical properties of solder joints,and have not considered the influence of the microstructure of the solder alloy on the mechanical behavior of the micro-solder joints.The difference in the mechanical behavior of the microstructure composition phase is still unclear.Therefore,there is an urgent need to carry out research on the micromechanical behavior of solder alloys with micro solder joints.In addition,the ever-decreasing volume of solder joints leads to a sharp increase in the current density in the solder joints,which causes electromigration and causes the solder joints to fail.Current density and temperature gradient are two important indicators that affect electromigration.Current test instruments cannot measure the size and distribution of current density and temperature gradient in the microstructure of micron-level solder joints,but most numerical simulations homogenize the solder joints.Chemical treatment,ignoring the difference in physical properties of the phase.In view of the above problems,this paper studies the micromechanical behavior of Sn58 Bi solder alloy,which is widely used in low temperature soldering of electronic packaging,and conducts thermoelectric coupling analysis.The full text research mainly includes the following three parts:1.According to the alloy phase diagram,the Sn58 Bi solder alloy and its constituent phases(Sn-rich phase and Bi-rich phase)solid solution alloys were prepared,and nanoindentation loading tests with different depths and different strain rates were performed.The load-displacement curve,elastic modulus and hardness values of the sample were obtained.Combined with finite element reverse analysis and dimensional theory,the relationship between the load-displacement curve of the compressed sample and the parameters of the compressed material stress-strain constitutive equation was established.The elastoplastic mechanical constitutive equations of Sn58 Bi solder alloy and its constituent phases under different strain rates and different loading depths were determined.2.Based on the Norton creep power law model,the load-displacement curve obtained from the nanoindentation test of the Sn58 Bi solder alloy and its constituent phases was analyzed during the load-holding stage,and the relationship between the hardness and the creep strain rate during the load-holding stage was determined.The logarithmic relationship point,through linear fitting,the slope obtained is the creep sensitivity index of the Norton creep power law model.In addition,the effects of nanoindentation size effect and different peak loads on the creep sensitivity index of Sn58 Bi solder alloy and its composition are also analyzed and studied.3.The methods of Monte Carlo and numerical image recognition were used to realize three-dimensional(3D)modeling and Two-dimensional(2D)modeling of Sn58 Bi microstructure respectively,and then the loading,solving and analysis were realized in ANSYS software.The size and distribution of current density and temperature gradient in Sn58 Bi micro solder joints were characterized quantitatively.