What is a Chip-Scale Package?

A Chip Scale Package (CSP) is a type of integrated circuit (IC) package that is surface mountable and has an area not more than 1.2 times the original die area. IPC/JEDEC's standard J-STD-012 for Implementation of Flip Chip and Chip Scale Technology states that to qualify as a chip scale package, the chip must be a single-die and have a ball pitch of not more than 1 mm.

CSP’s definition does not mention how it needs to be manufactured or constructed. Any package that meets the dimensional requirements of the definition and has surface mount ability can be considered a CSP. Structural dimensions are not given much consideration for classification as a chip-scale package. Because of this, there are a variety of chip-scale packages developed in the industry and generalized assumptions cannot be made on the manufacturability or reliability of the CSP as a homogeneous package group. There are over 50 different categories of chip-scale packages in the electronics industry which is continually evolving.

At the beginning of a typical CSP process, the die is mounted on the interposer using epoxy. The epoxy is usually of a non-conductive type although conductive epoxy is also used when the backside of the die needs to be connected to the circuit. The die is then wire-bonded to the interposer using gold or aluminum wires. These Wirebond profiles are as low and as close to the die as possible to minimize package size. This is followed by plastic encapsulation usually by transfer molding to protect the die and wires. After encapsulation, solder balls are attached to the bottom side of the interposer. Finally, the package is marked and the parts are separated from the lead frame.

CSPs offer advantages like smaller size (reduced footprint and thickness), lesser weight, relatively easier assembly process, lower overall production costs, and improvement in electrical performance. They are also tolerant of die size changes since a reduced die size can still be accommodated by the interposer design without changing the CSP's footprint.

CSP combines the strengths of various packaging technologies, such as the size and performance advantage of bare die assembly and the reliability of encapsulated devices. They are generally built using a lead frame which allows the assembly of many packages in bulk. This maximizes the use of the interposer area and allows many devices to be made from the same substrate. The significant size and weight reduction offered by the CSP makes it ideal for use in mobile devices like cell phones, laptops, palmtops, and digital cameras.