Flip chip (also known as direct chip attach) is the process whereby a semiconductor die is attached bond pad side down to a substrate or carrier. The electrical connection is made by means of a conductive bump on the die bond pad. Once the die is connected the stand-off distance between the die and substrate is typically filled with a non-conductive adhesive referred to as underfill. The underfill provides stress relief between the die and carrier, provides robustness, and protects the component from any moisture ingress.
Flip chip bonding can offer a number of advantages over other interconnection processes. Flip chip bonding can provide higher I/O count as the whole area of the die can be used for connections. Due to the short interconnections paths, compared to wire bonds, the speed of a device can be improved. In addition, as wire bonds loops are removed it provides a smaller form factor.