Research On Electro-migration Failure Of Flip Chip Under Electro-thermal-Structure Coupling

With the rapid development of Integrated Circuit technology,in order to meet the packaging requirements,the size of Flip Chip has become smaller and smaller,leading to the increasing current intensity in the package body,which makes the electro-migration phenomenon easily occur in the Integrated Circuit package.The electro-migration phenomenon usually occurs in the interconnection structure of micro flip chip package.Usually,the cavity is formed in the cathode.The cavity will lead to the crack in the package and destroy the integrity of the circuit,and the reliability of electronic products will be decreased.The miniaturization of packaging technology has a serious impact on the reliability of flip chip packaging,so it is of great significance to study and optimize the electro-migration failure of flip chip packaging.In this paper,according to the research method of electro-migration failure mechanism,an electro-migration reliability optimization technology is proposed to solve the reliability problem of flip chip package.This technology is based on the electro-thermal-structural coupling process of flip chip package,and combined with the influencing factors of electro-migration:resistivity,electro-migration resistance and current density.The simulation results show that the reliability of the flip chip package will be affected when the current density exceeds 1×10⁴A/cm².Firstly,the wiring pattern of copper wiring and the arrangement pattern of small solder balls in the flip chip package were optimized,and it was found that the current density of copper wiring in full connection mode was the least,and the electrical migration was improved most obviously.Secondly,copper alloy method is used to study the material of small and medium solder balls in flip chip packaging.When tin impurity is added into copper material and small solder balls are selected as Cu₃Sn and Cu₆Sn₅respectively,the simulation results show that Cu₆Sn₅ can improve the electro-migration failure more obviously.Then,the influence of the length,thickness and width of the copper wiring on the failure mechanism of electro-migration is analyzed.It is found that increasing the thickness and width of the copper wiring and reducing the length of the copper wiring can reduce the current density and improve the electro-migration,but the size of the copper wiring should meet the actual packaging requirements.At last,the viscoplastic ANAND constitutive model is introduced into the simulation to analyze the influence of different elastic or plastic materials on the final mechanical properties of the ANSYS simulation.It is found that the model is very helpful to the study of the stress-strain of the electro-migration failure of the flip chip package.Finally,the average failure time formula is optimized by introducing the generation and growth of cavities,and the simplified Black equation is used to calculate the failure life of electro-migration.Whether the electro-migration is improved or not is judged by the size of the average failure time.The finite element simulation results of the initial model and the improved model were put into the Black equation respectively.According to the calculation results,it is found that the electro-migration life is increased by 1.2 times after the optimization of the small solder ball material and 1.5 times after the optimization of the copper wiring connection.After optimizing the copper wiring width,the electric migration life is increased by 3 times,the electric migration life is increased by 7.5 times,and the electric migration life is increased by 8.4 times after optimizing the small copper wiring length.Because the operating temperature also has a great influence on the electro-migration failure,the calculation of the electro-migration life at high temperature shows that the electro-migration life decreases sharply with the increase of ambient temperature.