Current stressing effects on the reliability of Cu pillar bump with shallow solder

The intermetallic compound (IMC) growths of Cu pillar bump with shallow solder (thin Sn thickness) were investigated during annealing or current stressing condition. After reflow, only Cu
₆
Sn
₅
was observed, but Cu
₃
Sn formed and grew at Cu pillar/Cu
₆
Sn
₅
interface with increasing annealing and current stressing time. The kinetics of IMC growth changed when all Sn in Cu pillar bump was exhausted. The complete consumption time of Sn phase in electromigration condition was faster than that in annealing condition. Under current stressing condition, intermetallic compound growth was significantly enhanced mainly due to the joule heating effects. Kirkendall void was observed at the interface of Cu pillar/Cu
₃
Sn and it affected the mechanical reliability of Cu pillar bumps, which was estimated by die shear test.