Electromigration

**Electromigration EM Design Rules** is **a comprehensive set of interconnect design constraints that limit current density and current products in metal conductors — preventing accelerated conductor degradation from the momentum transfer of drifting electrons to metal atoms, which gradually transforms circuit interconnects into high-resistance or open-circuit structures**. Electromigration is a time-dependent failure mechanism where high current density in metal conductors causes progressive accumulation of metal atoms on one side of the conductor and depletion on the other side, eventually creating voids that increase resistance or break interconnect continuity. The electromigration current limit for specific metal layers and conductor widths is specified as maximum current density (amperes per square micrometer) that can be carried indefinitely at the maximum operating temperature without exceeding acceptable failure rates. The design rule for electromigration is typically specified as maximum current (in milliamps) that can flow through a conductor of specified width at specified temperature, with wider conductors allowing higher absolute current while maintaining the same current density limit. The thermal accelerations characteristic of electromigration require careful consideration of operating temperature, with electromigration failure rate doubling for every 50 degrees Celsius temperature increase, necessitating conservative derating for worst-case operating temperatures. The current distribution analysis for electromigration verification requires detailed electrical simulation across relevant frequency ranges and all possible circuit states, with particular attention to high-current paths that may not be immediately obvious from circuit topology. The multiple voltage domain operation and dynamic voltage scaling further complicate electromigration verification, requiring careful analysis of current distribution under all possible voltage and frequency combinations. **Electromigration design rules prevent degradation of metal interconnects through current density and temperature-dependent current limits.**