An ICT jig tester is a traditional electronic test fixture which has numerous pins inserted into holes in an acrylic which are aligned using tooling pins to make contact with test points on a printed circuit board and are also connected to a measuring unit by wires. These devices contain an array of small, spring-loaded pins; each pin makes contact with one node in the circuitry of the DUT (device under test). By pressing the DUT down against the fixture, reliable contact can be quickly and simultaneously made with hundreds or even thousands of individual test points within the circuitry of the DUT. The hold-down force may be provided by means of a vacuum or a mechanical presser, thus pulling the DUT downwards onto the nails.
Devices that have been tested on an ICT jig tester may show evidence of this after the process: small dimples (from the sharp tips of the pins) can often be seen on many of the soldered connections of the PCB.
The fixtures require a mechanical assembly to hold the PCB in place. Fixtures can hold the PCB with either a vacuum or pressing down from the top of the PCB. Vacuum fixtures give better signal reading versus the press-down type. The fixture, as generally termed, is used together with an in-circuit tester machine.