Electronics > Beginners

Pulling my hair out. Circuit boards stop working once shipped to client and more

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mcinque:

--- Quote from: Jackster on July 01, 2019, 04:29:22 pm ---I thought they did do that over x number of boards ordered?

--- End quote ---
Proabably. But it's the "every X boards" that makes the difference.

Of course class2 testing (all traces are tested individually) it's not included.

AndyC_772:
The shorted pins on the Wifi connector are certainly interesting, but they don't obviously explain your symptoms.

You've described cases where boards work for you but then stop working for your customer, or where swapping an apparently unrelated part can allow your CPU to program correctly (or not). Those symptoms aren't consistent with a bunch of shorted pins.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Some years ago, I was working for a company making fairly complex ISA cards for PCs. On one batch, we were seeing roughly a 25% failure rate during testing, and we traced the fault to a broken PCB trace in the exact same position on every board.

The boards were made locally by a reputable supplier, who invited us in for a meeting to discuss what had happened.

As it turned out, the board was made 4 up on a panel, and the master artwork for one of the layers had a scratch in just the same position as our fault. We pointed out that the boards were supposed to be 100% tested before shipment.

Upon questioning, the operator doing the testing admitted that he'd removed the test of that particular net because it was failing too often. He had neither checked a board manually by himself, nor told anyone else that there was a problem. The defect was on an outer layer, plainly visible and easy to check with a multimeter, so no excuse whatsoever.

If I recall correctly, the operator in question was fired, the artwork was reprinted and we had no more issues until the board was discontinued some years later.

Bare board test: *always* do it, *usually* believe it.

free_electron:
a couple of other things ( apart from the fouled up pcb spacing )

- not enough bulk capacitance in the design
- not enough local capacitance in design
- the crystal you use is a resonator. your processor fuse bits may need to be tuned for that ! check what the load capacitance and bleed resistor is in those things. you can buy those in different variants and the tuning needs to be done.
- aluminum case.... do you connect that electrically to your system ground ?

mcinque:

--- Quote from: AndyC_772 on July 01, 2019, 05:02:51 pm ---Upon questioning, the operator doing the testing admitted that he'd removed the test of that particular net because it was failing too often. He had neither checked a board manually by himself, nor told anyone else that there was a problem.

--- End quote ---
This is insane.

bd139:

--- Quote from: mcinque on July 01, 2019, 05:45:47 pm ---
--- Quote from: AndyC_772 on July 01, 2019, 05:02:51 pm ---Upon questioning, the operator doing the testing admitted that he'd removed the test of that particular net because it was failing too often. He had neither checked a board manually by himself, nor told anyone else that there was a problem.

--- End quote ---
This is insane.

--- End quote ---

If you think that’s insane come to the software industry. Unit test not working? Delete!

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