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Bed of Nails PCB Assembly Tester

By stienman
Created Oct 30 2006 - 2:30pm

A Bed of Nails tester is an array of spring loaded pins (pogo pins) that accept a circuit board. The circuit board is pressed down onto the pins, and each pin makes contact with a given pad or contact on the PCB. The other side of the pin connects to circuitry used to test the PCB.

Bed of nails testers are used in PCB fabrication to make sure all the traces and vias are complete, as well as PCB assembly to test proper operation of the circuit, and may also be used to program FLASH, EEPROMs, microcontrollers, and other parts after assembly.

Phil Eisermann responded to a recent inquiry on the PICList [1] on constructing a bed of nails tester:

We do 100% testing, so speed of test directly impacts cost. After designing several testers for various products, I developed a "generic" tester consisting of various modules like ADC, DAC, relays, buffers, etc. These modules plug into a motherboard of sorts (controlled by a PIC of course).

I've attached a few pics here. [The last picture, "PCBModules.jpg", is] a first generation prototype. Connecting the modules with wires gives you flexibility, but at the cost of a lot of time spent making wiring harnesses. And I mean a lot of time, not to mention mistakes in wiring or broken crimp terminals (and it does happen!)taking a lot of time to trace. I have version 2 being fabricated right now, which has headers for the modules to plug into, much like I/O cards for your motherboard. Makes assembly much quicker, but at the expense that the available signals are now fixed.

Click on the picture to see a much larger (2048x1536, between 100K and 200K each) version.






Hobbyist quantities of pogo pins may be found at Solar Robotics [7] under "Pins/Sockets.

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