used to project the electromigration lifetime under pulsed dc and ac current stressing has been reported. The experimental results indicate that different metallization systems (Al-2%Si, Al-4%Cu/TiW, and Cu) show similar failure behaviors, which can be explained and predicted by this model. The pulsed dc lifetime is found to be longer than dc lifetime, and the ac lifetime is found to be very much longer. This recognition can provide significant relief to circuit designs involving metals carrying pulsed dc and ac currents, and allow a more aggressive design to improve circuit density and speed. An electromigration failure model which can be.