What is Flip Chip

Flip Chip, known as controlled collapse chip connection, short of C4, is the way to interconnect semiconductor devices to external circuitry with solder bumps. The solder bumps are deposited on the chip pads on the upper side of the wafer during the final wafer processing procedure. In order to mount the chip to external circuitry, by flip chip package, the chip is flipped over so that the chip surface aligned directly with circuit board without wire bonding, and then the solder is reflowed to complete the whole interconnection.. Here is the processing steps:
1. Integrated circuits are created on the wafer
2. Pads are metalized on the surface of the chips
3. Solder dots are deposited on each of the pads
4. Chips are cut
5. Chips are flipped and positioned so that the solder balls are facing the connectors on the external circuitry
6. Solder balls are then remelted (typically using hot air reflow)
7. Mounted chip is “underfilled” using an electrically-insulating adhesive

Compared with wire bonding,, the whole processing steps of flip chip package can be completed in batch so as to reduce cost and improve the speed. The resulting completed flip chip assembly is much smaller than a traditional carrier-based system; the chip sits directly on the circuit board, and is much smaller than the carrier both in area and height. The short wires greatly reduce inductance, allowing higher-speed signals, and also conduct heat better.