A â€˜Chip-On-Boardâ€™ technology in which the silicon chip is inverted (â€˜flippedâ€™) and interconnected mechanically and electrically to a conductor pattern on the substrate by conductive bumps on the chip. The bumps are formed on the active surface of the chip, which is turned over for attachment. Flip-chip bumps are usually of solder, deposited on the bonding pads in vacuum, then reflowed. This process needs complex metallisation on the bonding pads. Originally developed by IBM, the process is also known as C4 (controlled collapse chip connection).