Electromigration failure mechanism of Sn96.5Ag3.5 flip-chip solder bumps

Abstract

The electromigration-induced failure of SnAg3.5 flip chip solder bumps was investigated at the current density of I x 10(4) A/cm(2) at 150 degreesC, and they failed after 22 hours of current stressing. Failure was found to be on anode/chip side, and large (Cu,Ni)(6)Sn-5 intermetallic compounds (IMCs) were observed on the interface of the UBM and the solder bump. A novel electromigration failure mechanism is proposed. Nickel atoms were migrated by electron flow from substrate side to chip side to form (Cu,Ni)(6)Sn-5 IMCs. The volume expansion due to the IMC formation may induce local high stress around the UBM and fail the contact of the anode/chip side.