Abstract: An endcap reservoir for extending electromigration lifetime and preventing harmful void formation that causes electromigration failure in interconnect lines. When a current is introduced into an interconnect line the current can drag metal atoms from behind the current flow down the interconnect line, leaving behind voids. Voids are regions of the interconnect line that no longer contain metal atoms. If a void grows to the entire width of the interconnect line it stops the current from flowing in the interconnect line and forces the current to flow in the shunt layer. Current flowing in the shunt layer raises the resistance of the interconnect line and can cause the interconnect line to suffer electromigration failure. The present invention, an endcap reservoir, is an extension of the interconnect line added at the upstream end of the interconnect line.