Reliability Investigation Of Lead-free Micro-electronic Packaging Solder Joint Under Electromigration

Under the tendency of miniaturization and multi-functionalization in electronic products,the current density of single solder joint loaded and the service temperature increased day byday. It brought a huge challenge to reliability of micro-electronic packaging solder joint. As anew failure mode of micro-electronic products, electromigration took wide concern gradually.The physics nature of electromigration was the atom in solder joint migrated in the directionof electron flow from cathode to anode continuously, under the droving of electronic wind.Electromigration can accelerate the failure of electronic component, cut down the effectiveservice lifetime, and seriously impact the reliability of micro-electronic packaging solderjoints.Based on the research above, under premise of excluding the interference of currentcrowing effect and joule heat effect, the paper used butting solder joint as study object, toinvestigate the influence on reliability of Cu/Sn-3.0Ag-0.5Cu/Cu solder joint in the loadingconduction of1.78×10~4A/cm~2current density and100℃. It was discovered that the growthof interfacial IMC at cathode and anode presented an obvious polarity effect under the currentstressing, the growth of interfacial IMC was strengthened at anode and inhibited at cathode. Itwas considered that the diffusion of Cu atom controlled the growth of interfacial IMC, underthe combined effects of electron wind, chemical potential gradient and back stress, the growthof interfacial IMC at anode presented a parabolic relationship with stressing time. The tensilestrength of solder joint declined with current stressing time, fracture mode changed form pureshear fracture to microvoid accumulation fracture, and finally to brittle fracture. The positionof fracture transferred from middle of solder to interfacial at cathode.As a comparative analysis, the Cu/Sn-3.0Ag-0.5Cu/Cu solder joint was used toinvestigate influence of isothermal aging on the reliability of solder joint. The result showedthat the interfacial IMC grew unceasingly with aging time; the higher the aging temperaturewas, the faster the interfacial IMC grew; the interfacial IMC growth speed was about1/30ofinterfacial IMC at anode in electromigration sample under the same temperature. The tensilestrength of solder joint decreased with aging time, the speed was about1/9ofelectromigration sample under the same temperature. For long time aging at high temperature, the Kirkendall voids were found at interfacial. The fracture mode changed form pure shearfracture to microvoid accumulation fracture, but the fracture position always appeared insolder. The interfacial IMC growth during aging at130℃of Cu/Sn-3.0Ag-0.5Cu/Ni solderjoint was also investigated. It was found that interfacial IMC at the side of Ni base metal grewmore slowly than the side of Cu base metal, the composition of interfacial IMC was verycomplex.Lastly, electromigration of Cu/Sn-9Zn/Cu solder joint under stressing condition of1.78×10~4A/cm~2current density and125℃was investigated. An abnormal phenomenon wasdiscovered that interfacial IMC grew both at anode and cathode, and the interfacial IMC grewfaster at cathode. It was considered that the diffusion of Sn atom controlled growth of IMC,when the interfacial IMC composition has been analysed.