SMD Quad Flat Pack QFP

- the quad flat pack or package, QFP provides an excellent format for high pin count SMD integrated circuits.

The Quad Flat Package, or Quad Flat Pack, QFP, is a package used for surface mount, SMD integrated circuits.

The QFP, Quad Flat Package is widely used because it enables SMD ICs with high numbers of interconnections to be used within electronics circuits.

The Quad Flat Package is an industry standard package format although a number of formats are available. These include variations on the number of pins, and also variations on other aspects of the package as well.

A surface mount quad flat pack or package, QFP mounted on a printed circuit board
Typical Quad Flat Package, QFP

Quad Flat Package, QFP Basics

The quad flat pack consists of a rectangular package a few millimetres thick. The package may be square with the same number of pins emanating from each edge or rectangular with different numbers of pins on each pair of sides..

The package itself is made from a top and a bottom section which are glue together. The connections emanate from the join on the side of the package. The pins are bent downwards towards the printed circuit board in what is termed a gull wing format. The pins normally just touch the printed circuit board so that they are easy to solder.

A surface mount quad flat pack or package, QFP lead configuration showing the gull wing shape
Quad Flat Package, QFP lead arrangement

Quad flat pack integrated circuits come in a variety of formats with pins varying in number. Often the QFP may be square and pin counts may rise to figures of 256 or even more. A 256 pin QFP would typically have 64 pins on each side. Some of the smaller quad flat packages may have pin counts of 32 pins, i.e. 8 pins on each side, assuming the package is square.

Quad flat package variants

There are many different abbreviations for the various formats for quad flat pack ICs. Some are detailed below:

  • BQFP - Bumpered Quad Flat Pack:   This form of quad flat package has extensions at the four corners to protect the leads against mechanical damage before the unit is soldered. One of the major problems with the QFP is the ease with which pins can be bent and damaged. Owing to the very fine pitch, it is very difficult and normally not economically viable to repair a device if the pins are bent.

    A surface mount bumbered quad flat pack on a PCB showing the corner extensions to protect the QFP pins
    Bumpered quad flat pack
  • BQFPH - Bumpered Quad Flat Pack with Heat spreader:   This form of quad flat package utilises the pin protectors at the corners, it also has heat spreaders to enable larger levels of power to be dissipated.
  • CQFP - Ceramic Quad Flat Pack:   This is a high quality version of the quad flat pack using ceramic for the package.
  • FQFP - Fine pitched Quad Flat Pack:   A quad flat pack with, as the name indicates, a fine pitch for the pins.
  • HQFP - Heat sinked Quad Flat Pack:   With many integrated circuits, especially those with high pins counts which have a high level of circuitry may dissipate high levels of heat. This heat may need to be removed. To achieve this a number of the pins, often in the centre of opposing sides are replaced with a thicker pin which is soldered to a large pad on the PCB with a large area of copper connected to it. This will remove a significant amount of heat.
  • LQFP - Low profile Quad Flat Pack:   The Low Profile Quad Flat Pack is based upon the metric QFP, MQFP, but it is are thinner with a body thickness or height of 1.4mm. This helps solve problems where component height may be a problem. It has a standard lead-frame footprint - 2.0mm lead footprint. Lead counts for the LQFP range from 32 to 256. Body sizes range from 5 x 5mm to 28 x 28mm. Lead pitches available for LQFP package are 0.3, 0.4, 0.5, & 0.65mm.
  • MQFP - Metric Quad Flat Pack:   A quad flat package where the measurements and in particular the pin spacing is defined in metric dimensions. Standard QFPs normally use Imperial measurements and have pin spacing etc defined in terms of convenient Imperial dimensions.
  • PQFP - Plastic Quad Flat Pack:   A quad flat pack where the package material is plastic. Some QFPs can use ceramic.
  • TQFP - Thin Quad Flat Pack:   The Thin Quad Flat Pack, TQFP is a form of low profile quad flat pack. Having a body thickness of 1.0mm and have a standard lead-frame footprint with 2.0mm lead footprint. The TQFP package material used is plastic.

QFP in use

The quad flat pack, QFP is widely used for many electronic circuits and assemblies. This form of package enables high numbers of interconnections to be accommodated around the device. With the growing complexity of many integrated circuits, this form of surface mount package enables the high connectivity levels required to be accommodated in a convenient format.

Although the QFP, quad flat package works well, there are a number of factors to be remembered when using it.

  • PCB track density:   The very high numbers of pins that can be accommodated by the QFP does mean that great care is required when designing the printed circuit board. The high pin count can lead to difficulties in track density around the device. Careful routing and design may be required to ensure that none of the design rules is violated.
  • QFP pin damage:   The pins on the quad flat package are small and closely spaced. It is easy for them to be damaged and deformed by poor handling. It is also very difficult to reform them correctly. To ensure damage is minimised they must be stored carefully - they are often shipped in special 'waffle' packing to provide adequate protection. This packaging can be used on the pick and place machines for assembling thereby ensuring that handling is minimised and the risk of damage reduced to the minimum.

In view of their advantages, quad flat packages are widely used within the electronics industry to enable the highly complex assemblies to be manufactured swiftly, efficiently and reliably.

By Ian Poole

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