Effects of Ag content on electromigration of Sn-Ag solder bumps in C4 package

In this study, the effect of Ag content (1.8 & 2.3 wt.%) on the electromigration lifetimes and microstructure evolution of Sn-Ag solder bumps were investigated at highly accelerated electromigration test conditions. Electromigration of solder joint under high current stressing has been an important concern of the reliabilities in solder joint system, since the higher device density and increasing power of flip chip package. The size of the bumps is reduced continuously, causing rapid increase in the current density passing through the bumps. During the high current stressing in solder joints, electromigration failure of the Sn-1.8Ag solder bumps occurred with large consumption of Ni under bump metallization (UBM) and void formation at the cathode side of the solder bump. The electromigration reliability of Sn-2.3Ag solder bumps was superior to that of Sn-1.8Ag solder bumps due to its slow consumption of solder joint and much longer lifetime.