This letter reports that electromigration lifetimes of Al–2Cu (wt. &percent;) thin-film conducting lines increase by more than three times when the lines are optimally aged to facilitate finely dispersedAl2Cuprecipitates in the interior of the grains. In contrast to other studies which did not report a beneficial aging effect for Al–Cu films, the present work substantiates the fact that proper control ofAl2Cuprecipitates improves resistance to electromigration failure. However, the benefit of aging the Al-2Cu lines investigated here was less pronounced and confined to a more narrow heat-treatment “window” than that previously found for the Al–2Cu–1Si lines. ©1998 American Institute of Physics.