diypcbtesting
When testing a complete circuit board a 'Bed of Nails' can significantly reduce time and errors.
What are some techniques for making a DIY Bed of Nails?
Specifically, looking for what kinds of materials work best, how to trace the board properly to make the holes in the right place, in other words, it's the little things that experienced people know but for a beginner would be a lifesaver.
I'm surprised this question is still lurking around. To definitely avoid tripping the building's earth leakage breaker use a local isolation transformer with a centre-tap on the secondary.
Also use a residual current trip device from the transformer secondary to the SMPSU you are testing. An RCD detects differences in voltages down the two live wires (aka Live and neutral) so you need to wire your SMPSU earth connection to the transformer secondary centre tap.
Should either of the two AC wires have an excessive current to earth the RCD will trip.
If both ac wires have equally excessive fault currents to earth (a less likely scenario) the RCD won't detect anything but neither would the ELCB because the currents balance.
CAUTION - working on live equipment can be dangerous and you need to ensure that the transformer centre-tap (pseudo earth) is grounded locally to protect yourself. However, this may still cause your distribution board's ELCB to trip - however, if you replace that ELCB with an RCD you should be OK.
In the semiconductor industry these are called DUT (for Device Under Test) or Load boards and they map from the ide pins to the tester standard connection format. They can be fairly expensive because of size and thickness (to ensure stiffness).
However, you don't need most of that. at the center of a DUT board are cantilevered comb like structures that are very stiff but are spaced at the 100 um pad pitch with 50 um tips. These are relatively inexpensive, no more than the cost of a single pogo-pin.
Here is a super fancy, RF matched and reinforced version:
If you look closely you can see a bunch of very fine fingers. Of course you can only use these under a microscope as you will bend the crap out of them if you hand place them.
here is what a old style DUT board looks like. A lot of the design is the interface to the system electronics, which you don't care about.
Originally pogopins were developed to contact the DUT board to the tester.
Here is a picture of wafer probe or probe fingers taken from UP patent 7688097 B2
This is still very fancy. I have seen these "combs" go for only a few $100's
Here are some picoprobe probecards from GGB industries which I've used.
And finally if you search on probecards you get lots of hits.
Best Answer
Having the board artwork helps, but if you don't, you can use a sacrificial blank PCB as your template.
Fix the blank PCB the appropriate way up, usually bottom side up, to your bed of nails substrate material. The latter needs to be thick enough to provide the mechanical stability. You can even use two layers for the bed of nails substrate, later separated by a gap, and mechanically joined together by the pogo-pins.
You can use good double sided tape to securely adhere the blank board to the substrates so they do not move relative to one another while you drill.
Then, using a drill press, drill holes wherever you need a test pin, through the PCB and on through the substrates. Use the appropriate sized drill bit for the pogo-pins.
You should also drill alignment holes for larger pins in the bed of nails that will mate with whatever mounting holes you have on the PCB. These pins on the bed of nails should be conical at the tips and longer than the pogo-pins so the board lines up BEFORE it makes contact with the test pins.