微量元素对无铅焊点电迁移性能的改善

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

电迁移现象已经成为电子组装焊技术中最受关注的问题之一.焊点在高电流密度下的服役可靠性与焊点钎料成分有关.通过对比分析五种SnAgCu基无铅焊点在高电流密度下的服役表现,分析了添加微量元素对于电迁移现象的影响规律.结果表明,焊球承受一定电流作用之后,阴极金属间化合物(IMC)分解,铜焊盘受侵蚀,阳极形成大量脆性化合物Cu6Sn5;根据IMC层的厚度变化,Sn3.0Ag0.5Cu的抗电迁移性能优于低银钎料;向低银钎料中加入微量元素Bi和Ni后,晶粒得到了明显的细化,界面IMC层较薄,其抗电迁移的能力得到了明显的改善.

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.