A laser-programmable multichip module on silicon

A laser-programmable substrate for multichip modules comprises a silicon substrate with a dense, predefined array of pads, tracks and links. A pattern of wiring connecting some of the pads is formed with a laser. Integrated circuit chips are mounted on the substrate, and the chip pads are wire-bonded to the substrate pads. East-west tracks are on the second level of metal, and north-south tracks on the first level. Power, ground, and signals share the tracks on the two metal layers. There is an array of 258-by-258 pads on a 200- mu m pitch, and there are three signal tracks, one power track, and one ground track between any two adjacent pads. Links consist of a silicon nitride layer sandwiched between the two metal layers. When a laser pulse of the correct power and duration is directed to the link region, the metal and nitride fuse to form a conductive vertical path, with a resistance typically two ohms.