Improvement electromigration resistance of Pb-free solder joints with element addition

Electromigration has become the most important concern for solder joint in electronic assembly.The solder joint durability under high current density stressing is highly dependent on the solder materials compositions.In this paper,the electromigration of five types of Sn based solder material were observed and compared.The influence of elements addition on solder electromigration were investigated.The results indicated that intermetallic compounds(IMC) was formed near the cathode disappeared after electromigration tests,and the copper layer at the cathode was consumed significantly.A large amount of Cu6Sn5 IMC were observed at the anode of the solder interconnects.Considering the IMC layer thickness as a criterion of electromigration durability,Sn3.0Ag0.5Cu solder performed better than low-Ag solder.By adding elements of Bi and Ni into the low-Ag solder,the solder microstructure were refined.The IMC accumulating near anode became thinner and electromigration resistance was improved significantly.