Suggestions and guidelines for DIY test fixture for high densidty PCB

[ricko_uk]

Hi,
I am designing a high density PCB (to the point of using 0402) and will also be designing and building a DIY test fixture (don't yet know the mechanical architecture yet - any suggestions also welcome!!) for it to use during development and also initial production testing and programming.

I am wondering about the following (any suggestions/tips) considering the test fixture will be DIY:
- smallest test pads size that still allows to use not too expensive probes
- preferred grid spacing to allow a relatively decent density while also make it not too difficult to assemble by hand (never done it before)
- any suggestions on the probes types (round tip, cone tip, different bodies perhaps) and a preferred or common brand/UK-distributor

Thank you

[ataradov]

The best test fixtures like this I had to work with were simple PCBs with holes for the spring loaded contacts and all the test points broken out to 0.1" connectors.

Make the PCB as thick as you can both for mechanical rigidity and for the ease of vertical probe alignment.

The smallest spring loaded contacts I've seen are 0.6 mm and 1.27 mm pads on both sides work like a charm with them. Bu they are quite fragile, so use the bigger size if you have space. The test pad should be fine at 1.27 mm either case.

No idea on the supplier, generic stuff from AlieExpress works fine and does not break a bank.

[Smokey]

Another thing to think about, and maybe more important than the actual connections to the boards, is... what mechanical process are you going to use to load the boards into the fixture, hold them down against the probes/pins, and remove them when finished.  If you make this system too complex/fragile/involved then you are in for some troubles if you plan on making this for "production".

Here is an example of a simple mechanical fixture.  It aligns and clamps the boards with one motion on that lid (as opposed to a bunch of screws, or multiple levers, or other such stuff that seems like a good idea until you actually have to use the thing you designed in your head).

https://www.automatiqsystems.com/versitraq.html


Another example:
https://www.testfixtures.com/pcb-test-fixtures/


As for the actual pogo pins, I would stay away from anything smaller than ones designed for 0.1" pin pitch holes.  I've used rows of the those into through holes and that worked ok.  They are pretty easy to damage if you aren't careful though.

Note:  Sorry, I remembered 2mm pitch but they were actually 0.1" pitch.