Flying probes for functional testing?

[ricko_uk]

Hi,
I always thought that flying probe testing is only for bare boards testing and for assembled PBCs only for assembly defects. But NOT for functional testing.
And always specified bed of nails testing when functional testing was needed.

But someone recently insisted that flying probe test systems can also do FULL functional testing which I don't even see how it can be possible given that the flying probe systems usually have only very limited number of probes...

Does anybody use flying probes for functional testing? Perhaps some limited type of functional testing?

Thank you

[Miti]

We do have FP but we don’t do powered testing. We only do parametric measurements, resistors, caps, diodes, shorts. There are options for power supplies though and they can do limited functional testing such as amplifiers gain, comparators, gates, transistors. You clip the power supply before beginning the test, and the program turns it on. However, I understand this is very uncommon.

[jbb]

I understand it’s possible, especially if the probe system has terminals to connect to external equipment (eg DMMs, programmers).

Most of the tests I’ve done on a bed-of-nails tester only really needed to connect to < 5 test points per individual test. So if you’re willing to move probes between tests that might work.

[ricko_uk]

Thank you Miti and Jbb

[ajb]

I guess there could be situations where the circuitry under test would be sensitive to unused probe lines hanging off of it (antennas, parasitic capacitance, external coupling...), so you only want specific points connected during a particular test.  Or maybe you need an active probe and either can't fit or don't want to pay for one at every point that needs testing and it's better to have one or two you can move around the board (I assume any worthwhile flying probe machine would be able to fit active probes?).  Or maybe there are mechanical reasons that a bed of nails won't work, like the board can't take the mechanical stress of the required number of test points, or you can't physically fit as many probes as you'd need.

In any case, seems like *full* functional testing with flying probes would be fairly slow versus a bed of nails where you can electronically multiplex test points or even just hook up more test gear so you can test more things at once, so even with the capability you would probably not want to use FP if you don't have to. 

[ricko_uk]

thank you ajb,
yes totally agree.

[jbb]

Yeah, I think flying probe would be slower per PCBA than a  bed of nails. As I understand it, the attraction is that you don’t need to fabricate a jig for each different PCBA. Could be good for low volume / high mix situations.