Stress voiding is caused by the difference in the thermal expansion coefficients of the metallization lines and the surrounding passivation. Volumes of individual stress voids are measured as a function of stress time at 200°C, 180°C, and 150°C in 1-μm-wide AlCu(1%wt) integrated circuit metallization lines. The time needed for void growth to saturate, and the total void volume depend on the stress temperature. If the void growth is regarded as an isothermal phase transformation in which voids are formed as precipitates at the void nucleation sites, the void volume growth is accurately described by the Avrami equation. Depending on the temperature, the time power n ranges between 0.5 and 1.5. First principle calculations are in excellent agreement with the measurements. The impact of the above results on electromigration testing is discussed.