In-circuit test (ICT) is an example of white box testing where an electrical probe tests a populated printed circuit board (PCB), checking for shorts, opens, resistance, capacitance, and other basic quantities which will show whether the assembly was correctly fabricated. It may be performed with a bed of nails type test fixture and specialist test equipment, or with a fixtureless in-circuit test setup.
There are many different test platforms for performing in-circuit test; for instance, Aeroflex 4220, 4230, 4250, Agilent 3070, i5000, i3070 Series 5, and i1000, Genrad (now part of Teradyne) TestStation, TS8x, 228x, Stinger, Teradyne, Spectrum 88xx, Z18xx, SPEA, Qmax Systems like QT200, QT8200, V200, V250, V2200, Digitaltest, SEICA, and Test Research Inc. TR5000 and TR8000 Series.
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A bed of nails tester is a traditional electronic test fixture which has numerous pins inserted into holes in an Epoxy phenolic glass cloth laminated sheet (G-10) 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. Named by analogy with a real-world bed of nails, these devices contain an array of small, spring-loaded pogo pins; each pogo pin makes contact with one node in the circuitry of the DUT (device under test). By pressing the DUT down against the bed of nails, 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 manually or by means of a vacuum, thus pulling the DUT downwards onto the nails.
Devices that have been tested on a bed of nails tester may show evidence of this after the fact: small dimples (from the sharp tips of the Pogo pins) can often be seen on many of the soldered connections of the PCB.
Typically, four to six weeks are needed for the manufacture and programming of such a fixture. Fixtures can either be vacuum or press-down. Vacuum fixtures give better signal reading versus the press-down type. On the other hand, vacuum fixtures are expensive because of their high manufacturing complexity. The bed of nails or fixture as generally termed is used together with a in-circuit tester.
This technique of testing PCB's is being slowly superseded by boundary scan techniques (silicon test nails), automated optical inspection, and built-in self-test, due to shrinking product sizes and lack of space on PCB's for test pads.
While in-circuit testers are typically limited to testing the above devices, it is possible to add additional hardware to the test fixture to allow different solutions to be implemented. Such additional hardware includes:
While in-circuit test is a very powerful tool for testing PCBs, it has these limitations:
The following are related technologies and are also used in electronic production to test for the correct operation of Electronics Printed Circuit boards