Plastic Ball Grid Array Package (pbga) Mechanical Properties Under Different Loading Conditions And Optimization Analysis

At present,while BGA(ball grid array) packages are widely applied to the field of microelectronic packaging,SMT(surface mounting technique) has gradually entered into the BGA package time.The failure of solder joints is the main reason for the failure of BGA assembly,while the PBGA package is the most widely used of the BGA package,so studying the reliability of PBGA package has a very important significance.In the first part of this paper,voltage values of PCB board,substrate and EMC for PBGA package under random vibration,thermal cycling,random vibration and thermal cycling compound conditions were measured through experiments,and strain values were calculated through the corresponding formula.So we used these values to analyze the strains under different environmental loading conditions.From analysis,it shows:Random vibration and thermal cycling compound conditions has the maximum strain value, random vibration condition has the minimum strain value which basically fluctuates in a narrow range,and the strain value under thermal cycling condition is between them.But the strain under compound condition is not only simply addition of that under random vibration and thermal cycling load condition.In the second part,we set up one-eighth structure model of PBGA package using finite element analysis software ANSYS,gave material parameters to each part of PBGA,then meshed the PBGA assembly,at last acquired one-eighth finite element model for PBGA package.After 0℃～100℃thermal cycle loading was imposed to PBGA assembly,we can analyze the equivalent strain distribution of each part for PBGA assembly,and find the most vulnerable failure solder joint through analyzing the plastic equivalent strain of solder joints.Based on this,we calculated the thermal fatigue life of solder joints by using the experimental Coffin-Manson formula.From the ANSYS simulation result,it shows:the maximum deformation of overall PBGA assembly lies at the outmost PCB board,and both the maximum equivalent stress and maximum plastic equivalent strain occur at the second solder joint of diagonal direction for one-eighth model,just at the bottom edge of silicon die. So this solder joint is considered as the solder joint which is the most prone to failure.As we all known that the lead-free solder joint has become the mainstream in microelectronics package in modern times,therefore,PBGA package with lead-free solder joint was studied in third part of this paper,and Taguchi method was used to optimize the structure parameters of PBGA package.Solder joint diameter,Size of PCB,Thickness of PCB,Size of substrate,Thickness of substrate,Thickness of silicon chip and Thickness of EMC eight factors was considered to experiment in Taguchi orthogonal arrays.We can calculate the effect of the plastic equivalent strain and find best control factor combination to achieve the target of decreasing the strain and reach for the purpose of PBGA package optimization.