What is "flip chip"

n. A method for interconnecting semiconductor devices to external circuitry with solder bumps that have been deposited onto the chip pads.

Flip chip, also known as controlled collapse chip connection or its abbreviation, C4, is a method for interconnecting semiconductor devices, such as IC chips and microelectromechanical systems (MEMS), to external circuitry with solder bumps that have been deposited onto the chip pads. The solder bumps are deposited on the chip pads on the top side of the wafer during the final wafer processing step. In order to mount the chip to external circuitry (e.g., a circuit board or another chip or wafer), it is flipped over so that its top side faces down, and aligned so that its pads align with matching pads on the external circuit, and then the solder is reflowed to complete the interconnect. This is in contrast to wire bonding, in which the chip is mounted upright and wires are used to interconnect the chip pads to external circuitry.

Flip-Chip modules were used in the DEC PDP-7 (referred to in documentation as the "FLIP CHIP"), PDP-8, PDP-9 and PDP-10, beginning on August 24, 1964. The trademark "Flip-Chip"' was filed on August 27, 1964. Various manuals produced by DEC refer to the modules as "FLIP CHIP", "FLIP-CHIP", "Flip Chip", and "Flip-Chip", with trademark and registered trademark symbols.

The first flip-chip modules mated with single-sided 18-contact card edge connectors with contacts on 1/8 inch centers. Circuit boards were 2 7/16 inches wide by 5 inches long, with a handle adding 1/2 inch. Double modules with two connectors end to end were 5 3/16 wide. Later, when two-sided boards were introduced, compatible double-sided 36-contact edge connectors were used, but the basic board dimensions were unchanged.

The modules were called Flip-Chips because early versions of some of these modules, for example, the R107 module shown, used hybrid integrated circuits built using flip chip mounting of individual diode chips on a ceramic substrate. Some boards containing flip chip modules were etched and drilled to allow those modules to be replaced by discrete components. At some points during production, conventional discrete components may have replaced these flip-chip devices, but the early use of hybrid integrated circuits allowed DEC to market the PDP-8 as an integrated circuit computer.

When DEC began to use monolithic integrated circuits, they continued to refer to their circuit boards as "Flip-Chip" modules, despite the fact that actual flip chip mounting was not used. DEC continued to hold the flip chip trademark until June 6, 1987, when the trademark was allowed to expire.