A chip packaging technique in which the active area of the chip is "flipped over" facing downward. Instead of facing up and bonded to the package leads with wires from the outside edges of the chip, any surface area of the flip chip can be used for interconnection, which is typically done through metal bumps of solder, copper or nickel/gold. These "bumps" or "balls" are soldered onto the package substrate or the circuit board itself and underfilled with epoxy. The flip chip allows for a large number of interconnects with shorter distances than wire, which greatly reduces inductance.
Wire Bond Vs. Flip Chip
In the wire bond method (top), the die faces up and is attached to the package via wires. The flip chip (bottom) faces down and is typically attached via solder bumps similar to the larger ones that attach BGA packages to the printed circuit board (also shown here). (Image courtesy of Amkor Technology, Inc.)