Characterization Of Void In Lead-Free Solder Joint And Its Effects Of Void On Damage And Failure

In the field of microelectronic packaging,the reliability of solder joint has been a research hot spot.Mismatches in the coefficients of thermal expansion(CTE)of different material will lead to damage such as creep damage and fatigue damage when it exposed to temperature cycling.This damage failure behavior is the key point of the solder joint research.The presence of voids would have a huge impact on the failure behavior of solder joints.This paper studied the influence of voids on the mechanical properties and fatigue life of lead-free solder.Meanwhile,the inverse analysis method was used to analyze the void volume fraction of solder joint.The major works and results are listed as follows:(1)The finite element(FE)model of Lead-free solder tensile rod was built,and the features of void were also taken into account.According to tensile stress model under different porosity,which's stress-strain curve inversion identify the content of lead-free solder hole stretch stick.The results of three inverse examples show that the error of void volume fraction identification is small,and the feasibility of using the inverse method to study the inner voids of the material is therefore demonstrated.(2)An inverse analysis method based on the Kalman Filter(KF)algorithm and uniaxial tension experiment was proposed.In this method,the load-displacement curves from uniaxial tensile test were used in combining with finite element simulation to determine the void volume fraction of solder layer.An improved cohesive zone model was proposed to analyze the bonding property of copper-solder interface.The results show that the inverse analysis method has advantages of higher efficiency and lower error in the identification of the void volume fraction of solder layer.(3)A DCB model with interfacial voids was developed to investigate the influence of void location on crack propagation and fatigue life.An irreversible cohesive zone model was proposed to predict the fatigue crack path and damage evolution process of solder interface.In addition,the effect of different void contents was also taken into consideration.With these studies,the relationship among voids,crack propagation and fatigue life can be revealed.(4)A package model with voids in the solder joint was established.The effect of different parameters was studied,like different void volume fractions,different thicknesses of solder layer and different solder materials with the same void volume fraction.The results show that with the increase of void volume fraction,fatigue life of solder will decreases.However,as the increase of void volume fraction,the trend of solder fatigue life decreasing becomes slow.The package model with thicker solder layer has better adaptability to the void.The nano-silver sintering has a better fatigue performance and a better adaptability for voids,as compared with Sn-3.0Ag-0.5Cu(SAC305).