Could it be possible that the mounting screw, the washer beneath it (if
there was one) or the opposite side boss or mounting surface in contact
with the PCB shorted to an external GND conductor that was too close to
the hole, washer or opposing feature? It sounds like a mechanical
interference with an external conductor.

>----------
>From:  Bock Ming Gai Joanne[SMTP:[log in to unmask]]
>Sent:  Tuesday, September 01, 1998 3:17 AM
>To:    [log in to unmask]
>Subject:       [DC] Short Circuit
>
>Hi all,
>
>Currently I'm facing a problem at work. I have a few 6 layers of PCBs
>that are perfectly alright, meaning that they passed the ET. However,
>when our engineers did some testing after board assembly, problem
>surface. When they tighten the board with mounting screws, they found
>that one of the supply trace was shorted to the Gnd. This was not shown
>during the ET because PCB suppliers only did the test on the bare
>boards. So now I am looking into what could possibly cause them to short
>together.
>
>I appreciate anyone who can help to provide me with a solution.
>
>Thanks & Best Regards!
>Joanne Bock
>
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