We propose a methodology using nodal analysis techniques compatible with existing computer-aided design (CAD) tools for implementing critical threshold design rules for electromigration reliability. The concept underlying critical threshold design rules is the observation that a mechanical stress-induced backflow of metal atoms is created by electromigration in interconnect lines confined by a rigid dielectric. If the steady-state balance of these two atomic fluxes is achieved before critical electromigration damage is realized, then the line can be considered to be virtually immortal with negligible reliability risk. A design rule based on this critical threshold criterion has the potential to give designers added flexibility to use currents larger than present design rules typically allow in short interconnects.