Electromigration study of eutectic SnPb flip-chip solder joints on ceramic substrates

This study investigates electromigration Study of eutectic SnPb flip-chip solder joints on ceramic substrates. The under bump metallization (UBM) structure consist,; of 5-mu m Cu / 3-mu m Ni under bump metallization (UBM). Under the current stressing by 0.9A tit 150 degrees C, we did not find void formation but a large amount of intermetallic compound (IMC) of Cu-6(Sn, Ni)(5) were fornied when the bump resistance increased 10 m Omega. Three-dimensional electrical Simulation by finite element analysis was carried out to simulate the current density distribution in solder joints with slit Cu traces. It is found that the current density was almost uniformly distributed in solder joint for this structure. It is found that the bump resistance only increases 0.07m Omega when half of the solder bump was transformed into Cu6Sn5 IMC. The reason for the low crowding effect in the solder joints will be discussed in the conference.