Flip-Chip is 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. These bumps are soldered onto the package and underfilled with epoxy. The Flip-Chip allows for a large number of interconnects with shorter distances than wire, which greatly reduces inductance.
According to Lionel Cadix, market and technology analyst, Yole Developpement, France, metal bumps can be made of solder (tin, tin-lead or lead-free alloys), copper, gold and copper-tin or Au-tin alloys. The package substrates are epoxy-based (organic substrates), ceramic based, copper based (leadframe substrates), and silicon or glass based.
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