Characterization of Solder Joint Electromigration for Flip Chip Technology

摘要

Electromigration behavior and current carrying capabilities of eutectic Sn-37Pb, Sn-3.5Ag, and Sn-3.8Ag-0.7Cu solders on electroless NiP / immersion Au under bump metallurgy were investigated in a flip chip configuration. None of the solders showed electromigration failure when tested at up to 2.55×10{sup}4 A/cm{sup}2 and 150°C for 2338 hours. At 170°C, some SnAg bumps had a three times increase in electrical resistance under same current/time stress condition. Pb tends to migrate with electron flux to form a Pb-rich phase at the anode of the SnPb flip chip joint. At a current density greater than 5.1×10{sup}4A/cm{sup}2 at 150°C, the current carrying capability of all bumps deteriorated dramatically and there were significant phase separation accompanied by aggressive intermetallic growth. The entire NiP UBM migrated toward anode and formed a Sn-Ni intermetallic after only 30 hours of stressing at 5.1×10{sup}4A/cm{sup}2 and 150°C, that may be a reliability concern for the NiP UBM. Voids were found at the interface of lead-free solder whereas eutectic SnPb solder had very few voids after electromigration testing.