A comparison study of electromigration in In-48Sn solder interconnects with Cu and Au/Ni/Cu pads

The microstructural evolution and interfacial reactions of the eutectic In-48Sn solder interconnect with Cu and Au/Ni/Cu pads, under current stressing of 0.7×104 A/cm2 at room temperature, have been investigated. The Ni metallization eliminated the current density inside the solder bump region, which is helpful to improve the electromigration reliability. During electromigration, Sn migrated to anode, while In migrated to cathode. The opposite migration direction of Sn and In atoms led to the segregation of Sn-rich and In-rich phases. The interfacial IMCs in the solder interconnect with Cu pads were composed of Cu6(Sn,In)5 and Cu(In,Sn)2. The most noticeable characteristic with using Cu pads was the spalling of thick cathode IMC, which was caused by the dissolution of cathode Cu. In the interconnect with Au/Ni/Cu pads, only a thin layer of (Ni,Cu)3(Sn,In)4 was formed at both the cathode and anode interfaces. The cathode dissolution is significantly eliminated by using Au/Ni/Cu pad, which improved the electromigration resistance of In-48Sn solder interconnects.