A flip chip also known as the Controlled Collapse Chip Connection, or C4 is one type of mounting used for semiconductor devices, such as IC chips, MEMS or components, which is using solder bumps instead of wire bonds. Semiconductor devices are Electronic components that exploit the electronic properties of Semiconductor materials principally Silicon, Germanium Microchipsjpg|right|thumb|200px|Microchips ( EPROM memory with a transparent window showing the integrated circuit inside Microelectromechanical systems ( MEMS) is the technology of the very small and merges at the nano-scale into Nanoelectromechanical systems (NEMS and Nanotechnology A solder is a fusible metal Alloy with a melting point or melting range of 90 to 450 ° C (200 to 840 ° F) used in a process called Wire bonding is a method of making interconnections between a microchip and other electronics as part of semiconductor device fabrication. The solder bumps are deposited on the chip pads, located on the top side of the wafer, during the final wafer processing step. A wafer is a thin slice of Semiconductor material such as a Silicon crystal used in the fabrication of Integrated circuit and other microdevices In order to mount the chip to external circuitry (on a circuit board or another wafer or a chip), it is flipped around – the top-side facing down the mounting area. The solder bumps are used to connect directly to the associated external circuitry.

Process steps

• Integrated circuits are created on the wafer
• Pads are metalized on the surface of the chips
• Solder dots are deposed on each of the pads
• Chips are cut
• Chips are flipped and positioned so that the solder balls are facing the connectors on the external circuitry
• Solder balls are then remelted (typically using ultrasound)
• Mounted chip is “underfilled” using an electrically-insulating adhesive

Comparison of mounting technologies

Wire bonding

The interconnections in a power package are made using thick aluminium wires (250 to 400 µm) wedge-bonded

In typical semiconductor fabrication systems chips are built up in large numbers on a single large "wafer" of semiconductor material, typically silicon. Semiconductor device fabrication is the process used to create chips the Integrated circuits that are present in everyday Electrical and electronic The individual chips are patterned with small pads of metal near their edges that serve as the connections to an eventual mechanical carrier. The chips are then cut out of the wafer and attached to their carriers, typically with small wires (see wire bonding). Wire bonding is a method of making interconnections between a microchip and other electronics as part of semiconductor device fabrication. These wires eventually lead to pins on the outside of the carriers, which are attached to the rest of the circuitry making up the electronic system.

Flip chip

Side-view schematic of a typical flip chip mounting

The processing of a flip chip is similar to conventional IC fabrication with the addition of a few additional steps. ^[1] Near the end of the process the attachment pads are "metalized" to make them more suitable for being soldered onto. This typically consists of several treatments. A small dot of solder is then deposited on each of the pads. The chips are then cut out of the wafer as normal. No additional processing is required, and there is no mechanical carrier at all.

To attach the flip chip into a circuit, it is inverted to bring the solder dots down onto connectors on the underlying electronics or circuit board. A printed circuit board, or PCB, is used to mechanically support and electrically connect Electronic components using conductive pathways or traces The solder is then re-melted to produce an electrical connection, typically using an ultrasonic process. This also leaves a small space between the chip's circuitry and the underlying mounting. In most cases an electrically-insulating adhesive is then "underfilled" to provide a stronger mechanical connection, provide a heat bridge, and to ensure the solder joints are not stressed due to differential heating of the chip and the rest of the system.

Advantages

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.

Disadvantages

Flip chips have several disadvantages as well. The lack of a carrier means they are not suitable for easy replacement, or manual installation. They also require very flat surfaces to mount to, which is not always easy to arrange, or sometimes difficult to maintain as the boards heat and cool.

History

The process was originally introduced commercially by IBM in the 1960s for ICs being used in the mainframe systems. International Business Machines Corporation abbreviated IBM and nicknamed "Big Blue", is a multinational Computer Technology ^[2] DEC followed IBM's lead but was unable to achieve the quality they demanded, and eventually gave up on the concept. In the 1970s it was taken up by Delco Electronics, and has since become very common in automotive applications. Delco Electronics Corporation was the automotive Electronics design and manufacturing subsidiary of General Motors based in Kokomo Indiana.

Alternatives

Since then a number of alternatives to the solder bumps have been introduced, including gold balls or molded studs, electrically conductive plastics, and the "plated bump" process that removes an insulating plating by chemical means. Flip chips have recently gained popularity among manufacturers of cell phones, pagers and other small electronics where the size savings are valuable. A pager (sometimes called a beeper) is a simple personal Telecommunications device for short messages

References

1. ^ Solder Bump Flip Chip
2. ^ Introduction to Flip Chip: What, Why, How

See also

• Solid Logic Technology
• Wikihowto: Guide to IC packages

External links

• Flip chip tutorials
• Flip Chip Assembly
• Flip Chip (C4) Benefits
• Kyocera America, Inc. - White Paper: Flip Chip Challenges