This technique of testing PCBs is being slowly superseded by boundary scan techniques (silicon test nails), automated optical inspection, and built-in self-test, due to shrinking product sizes and lack of space on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. But in mass production, test point diameters of 1.0 mm or higher are normally used to minimise contact failures leading to lower remachining costs. Fixtures with a grid of 0.8 mm for small nails and test point diameter 0.6 mm are theoretically possible without using special constructions.
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The bed of nails or fixture, as generally termed, is used together with an in-circuit tester.
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Moreover, vacuum fixtures cannot be used on bed-of-nails systems that are used in automated production lines, where the board is automatically loaded to the tester by a handling mechanism. On the other hand, vacuum fixtures are expensive because of their high manufacturing complexity. Vacuum fixtures give better signal reading versus the press-down type. Fixtures can hold the PCB with either a vacuum or pressing down from the top of the PCB. The hold-down force may be provided manually or by means of a vacuum or a mechanical presser, thus pulling the DUT downwards onto the nails.ĭevices that have been tested on a bed of nails tester may show evidence of this after the process: small dimples (from the sharp tips of the Pogo pins) can often be seen on many of the soldered connections of the PCB.īed of nails fixtures require a mechanical assembly to hold the PCB in place.
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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. 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). 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.