A flip chip is one type of IC chip mounting which does not require any wire bonds. Instead the final wafer processing step deposits solder beads on the chip pads. After cutting the wafer into individual dice, the "flip chip" is then mounted upside down in/on the package and the solder reflowed. Flip chips then normally will undergo an underfill process which will cover the sides of the die, similar to the encapsulation process. The terminology flip chip originates from the upside down (i.e. flipped) mounting of the die. This leaves the chip pads and their solder beads facing down onto the package, while the back side of the die faces up. This mounting is also known as the Controlled Collapse Chip Connection, or C4.
Flip-Chip® modules were used in the DEC PDP-7, PDP-8, PDP-9 and PDP-10, beginning on August 24, 1964. The modules were called Flip-Chip because early versions of some of these modules used flip chip mounting for discrete diode chips, but were eventually found to be unreliable so conventional discrete diodes replaced the flip chips. In later computers where DEC used integrated circuits they continued to use "Flip-Chip®" despite the fact that actual flip chip mounting was not used so that they could retain their trademark. Eventually the trademark was allowed to expire.