A quad flat package (QFP) is a surface-mounted integrated circuit package with "gull wing" leads extending from each of the four sides. Socketing such packages is rare and through-hole mounting is not possible. Versions ranging from 32 to 304 pins with a pitch ranging from 0.4 to 1.0 mm are common. Other special variants include low-profile QFP (LQFP) and thin QFP (TQFP). The QFP component package type became common in Europe and United States during the early nineties, even though it has been used in Japanese consumer electronics since the seventies. It is often mixed with hole mounted, and sometimes socketed, components on the same printed circuit board (PCB). A package related to QFP is plastic leaded chip carrier (PLCC) which is similar but has pins with larger pitch, 1.27 mm (or 1/20 inch), curved up underneath a thicker body to simplify socketing (soldering is also possible). It is commonly used for NOR flash memories and other programmable components. Limitations The quad flat-pack has connections only around the periphery of the package. To increase the number of pins, the spacing was decreased from 50 mil (as found on small outline packages) to 20 and later 12 (1.27 mm, 0.51 mm and 0.30 mm respectively). However, this close lead spacing made solder bridges more likely and put higher demands on the soldering process and alignment of parts during assembly. The later pin grid array (PGA) and ball grid array (BGA) packages, by allowing connections to be made over the area of the package and not just around the edges, allowed for higher pin counts with similar package sizes, and reduced the problems with close lead spacing. Variants The basic form is a flat rectangular (often square) body with leads on four sides but with numerous variation in the design. These differ usually only in lead number, pitch, dimensions, and materials used (usually to improve thermal characteristics). A clear variation is bumpered quad flat package (BQFP) with extensions at the four corners to protect the leads against mechanical damage before the unit is soldered. Heat sink quad flat package, heatsink very thin quad flat-pack no-leads (HVQFN) is a package with no component leads extending from the IC. Pads are spaced along the sides of the IC with an exposed die that can be used as ground. Spacing between pins can vary. A thin quad flat pack (TQFP) provides the same benefits as