Relocating, or redistributing, contact points is another technology that can be done efficiently at the wafer level. A redistribution layer (RDL) is used to reroute connections to desired locations. For example, a bump array located in the center of a chip can be redistributed to positions near the chip edge. The ability to redistribute points can enable higher contact density and enable subsequent packaging steps. This “fan-in” process also creates one of the smallest packages available.
The redistribution process adds another set of layers over the wafer surface. A dielectric film is deposited for electrical isolation, then the original bond pads are exposed. Metal lines are deposited to relocate the pads to desired locations, and under bump metallization (UBM) layers are built to support the solder bumps.