Routing (electronic design automation)

Routing, commonly called wire routing, is the step in the design of printed circuit boards and integrated circuits that adds the wires needed to connect components already positioned by the preceding placement step, while obeying every design rule. Together the two steps are known as place and route. A router is given pins on cells grouped into nets, obstacles where wires cannot go, and sometimes preroutes, and it must connect all terminals of a net without joining different nets, leaving no opens, shorts or design rule violations, while also meeting timing, crosstalk, metal density and antenna limits. Almost every routing problem is known to be intractable: even the simplest, the Steiner tree problem for one net in one layer, is NP-complete, so most algorithms are heuristics. Autorouter families include maze routers, Lee routers, channel routers and topological routers, and a common detailed method is rip-up and reroute.