Electromigration in Flip-chip SnPb Solder Joints with thick Ni/Cu UBM

Flip Chip Technology is one of the most important packaging methods for high current density IC device. While current density applied increased, solder joint has become a critical issue on device reliability. Concerning electromigration, the device design rule requires that each solder bump need to carry 0.2A to 0.5A, and the current density will reach 1000~10000 A/cm2 in the future. However, there are few studies on solder EM with thick UBM structure (Ni/Cu).

In this study, Sn80/Pb20 solder joints with thick UBM (electroplating Ni 3µm/Cu 5µm) were stressed at 1000~10000 A/cm2 at 150C. The bump height was about 70µm, and electroless Ni 3µm was adopted as barrier layer at board side. It is found that the dissolution of UBM was the failure mechanism for the solder joints with thick film UBM. The details of results will be presented in this meeting.