PLCC, Plastic Leaded Chip Carrier

- essential notes or overview about the SMD PLCC, Plastic Leaded Chip Carrier, an SMT package that can be soldered to a board or used with a socket.

The SMD PLCC or Plastic Leaded Chip carrier is an SMD package that is widely used for many types of integrated circuit. However the SMD PLCC is particularly useful for applications where the integrated circuit may need to be removed on a regular basis as, for example, in the case of a chip containing firmware where no other means of re-programming may be available.

The SMD PLCC also has the advantage that it can be soldered to the board. Having leads on all sides of the chip, the SMD PLCC offers a relatively high connection density.

SMD PLCC basics

An SMD PLCC or plastic leaded chip carrier is a four sided flat integrated circuit package or chip carrier. Rather than using the gull wing leads that are used on the quad flat pack, the SMD PLCC uses a "J" lead format. Here the leads are in the form of a J that is positioned on the edge of the SMD PLCC package with the lower section of the J folding back under the package.

As a result of the lead format the SMD PLCC offers a number of advantages:

  • Space saving:   The "J" lead of the SMD PLCC provides a useful reduction in board area when compared to the gull wing lead of the QFP. As the "J" lead effectively folds back under the package, this provides a significant reduction in real estate usage.
  • Socket compatible:   In some areas, especially when developing new products a socketed chip can be particularly useful, if new builds of a PLD or other chip may be needed. The PLD can be programmed off the board and added to the board to test the overall system operation. While many boards will allow on-board programming, this may not always be achievable.
  • Heat resistance:   In some limited instances, the heat experienced during the soldering process could cause damage to the chip. In this case a socket can be added to the board, and the PLCC inserted after soldering is completed, and no high temperatures will be experienced.

The SMD PLCC can have a variety of formats. Lead counts can vary from 20 up to 84 and body widths range from 0.35 to 1.15 inches. Pin or lead spacing is generally 0.05 inches, i.e. 1.27 mm.

PLCC sockets

One of the major advantages of an SMD PLCC is that the chip can be connected to the circuit via a socket. The same chip format can also be used in the standard SMT format, soldering the PLCC directly to the board. This can have significant advantages when a replaceable chip is needed for development, but then the same chip can be used in production where it can be soldered onto the board.

PLCC sockets may either be surface mounted - the most common, or some through hole versions are also available. Some through hole PLCC sockets may be used with wire wrap techniques for prototyping.

Although it is often possible to extract PLCCs using a small screwdriver, etc., it is far more preferable to use a PLCC extractor tool. This will make extraction of the PLCC far easier, and minimise the possibility of any damage.

By Ian Poole

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