It sounds like you have possibly not gotten enough clearance around the
mounting holes on the Internal Layers. You should be able to visually verify
if any exposed internal layer copper is present in the mounting holes. Are
the screws that are being used metal or nylon? If metal try using nylon.
Does the short go away when you remove the screw? Is there any significant
Bow or Twist when the board is installed in the housing? Try installing the
bare board in the housing and see if the same signals short out. These are a
couple of suggestions to find the problem.


Paul Brionez
Sr. PCB Designer
Cherry Electrical Products
11200 88th Ave
Pleasant Prairie, WI 53158
PH 414-942-6659
Fax 414-942-6334
[log in to unmask]

> -----Original Message-----
> From: Bock Ming Gai Joanne [SMTP:[log in to unmask]]
> Sent: Tuesday, September 01, 1998 2:17 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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