What is electromigration and how is it addressed in VLSI?

Electromigration (EM) is metal atom movement due to electron momentum transfer in high-current-density wires, causing voids (open circuits) or hillocks (shorts). Affected by: Current density, temperature, wire material and structure. EM analysis compares current through wires against EM limits defined by foundry reliability models (typically for 10-year lifetime). Mitigation: Wider wires for high-current paths, proper via arrays, limit DC current density, and use Cu instead of Al. Signoff requires EM-clean designs. Also consider: ESD, hot carrier injection, and NBTI for reliability.