Zero insertion force (ZIF) is a concept used in the design of IC sockets and electrical connectors invented to avoid problems caused by applying force upon insertion and extraction.
A normal integrated circuit (IC) socket requires the IC to be pushed into sprung contacts which then grip by friction. For an IC with hundreds of pins, the total insertion force can be very large (tens of newtons), leading to a danger of damage to the device or the circuit board. Also even with relatively small pin counts each extraction is fairly awkward and carries a significant risk of bending pins (particularly if the person performing the extraction hasn't had much practice or the board is crowded). Low insertion force (LIF) sockets reduce the issues of insertion and extraction but the lower the insertion force of a conventional socket, the less reliable the connection is likely to be.
With a ZIF socket, before the IC is inserted, a lever or slider on the side of the socket is moved, pushing all the sprung contacts apart so that the IC can be inserted with very little force (generally the weight of the IC itself is sufficient with no external downward force required). The lever is then moved back, allowing the contacts to close and grip the pins of the IC. ZIF sockets are much more expensive than standard IC sockets and also tend to take up a larger board area due to the space taken up by the mechanism. Therefore they are only used when there is a good reason to do so.
Large ZIF sockets are only commonly found mounted on PC motherboards (from about the mid 1990s forward). These CPU sockets are designed to support a particular range of CPUs, allowing computer retailers and consumers to assemble motherboard/CPU combinations based on individual budget and requirements. The rest of the electronics industry has largely abandoned sockets and moved to surface mount components soldered directly to the board.
Smaller ZIF sockets are commonly used in chip-testing and programming equipment, e.g. programming and testing on EEPROMs, Microcontrollers, etc.
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Standard DIP packages come in two widths (measured between pin centers), 0.3 in (7.62 mm) (skinny dip) for smaller devices (8-28 pin) and 0.6 in (15.24 mm) for larger devices (24-40 pin). To allow design of programmers and similar devices that supported a range of devices some in skinny dip and some in full width dip universal test sockets are produced. These have wide slots into which the pins drop allowing both 0.3 in and 0.6 in devices to be inserted.
ZIF sockets can be used for ball grid array chips, particularly during development. These sockets tend to be unreliable, failing to grab all the balls. Another type of BGA socket, also free of insertion force but not a "ZIF socket" in the traditional sense, does a better job by using spring pins to push up underneath the balls.
ZIF wire-to-board connectors are used for attaching wires to printed circuit boards inside electronic equipment. The wires, often formed into a ribbon cable, are pre-stripped and the bare ends placed inside the connector. The two sliding parts of the connector are then pushed together, causing it to grip the wires. The most important advantage of this system is that it does not require a mating half to be fitted to the wire ends, therefore saving space and cost inside miniaturised equipment. See flexible flat cable.
ZIF tape connections are used for connecting IDE and SATA disk drives (mostly 1.8" factor). ZIF-style connectors for IDE hard drives were used primarily in the design of Ultra-Portable notebooks, and has since been phased out, as SATA has a relatively small-form-factor connector by default. Also, nearly all hard drives use ZIF tape to connect their circuit board to their platter motor.
Three types of ZIF connectors are known to exist on 1.8" drives. ZIF-24, ZIF-40, and ZIF-50 with 24, 40, and 50 pins respectively.
ZIF tape connections are also heavily used in the design of the Apple Inc. iPod range of portable media players.