For Al-Cu VLSI interconnects at tungsten (W) plug contact/via areas, a new electromigration (EM) failure model has been established. A series of experiments was performed to verify the proposed model using novel test structures. This paper discusses the lifetime extrapolations using the model and experimental data which predicts that lifetimes of AI-Cu interconnects at use conditions are dominated by Cu drift, or incubation times. This paper also discusses EM experimental results obtained for the Al-filled via which is a promising candidate for replacing W plug vias due to requirements of process simplification and cost reduction in multilevel metallizations. EM failure distributions from Al-filled vias show large standard deviations. This observation is explained through extensive failure analysis of EM-failed specimens. The application of the established EM model to Al-filled vias is discussed.