Electromigration activation energy is measured by a built-in sensor that detects the real temperature during current stressing. Activation energy can be accurately determined by calibrating the temperature using the temperature coefficient of resistivity of an Al trace. The activation energies for eutectic SnAg and SnPb solder bumps are measured on Cu under-bump metallization (UBM) as 1.06 and 0.87 eV, respectively. The activation energy mainly depends on the formation of Cu-Sn intermetallic compounds. On the other hand, the activation energy for eutectic SnAg solder bumpswith Cu-Ni UBM is measured as 0.84 eV, which is mainly related to void formation in the solder.