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March 1998

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Subject:
From:
Aric Parr <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Wed, 11 Mar 1998 15:35:55 EST
Content-Type:
text/plain
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text/plain (87 lines)
Years ago,

I once had a lot of panels where there were resin voids bridged traces
under the soldermask. These filled up with foam flux (or water from the
wash) and never completely dried. Since the panel had 30 Mohm circuits, we
had intermittant shorts caused by flux and water inside the PCB. This is
the only "flux short" that I have seen.

Aric
-------------
Original Text
From: C=US/A=INTERNET/DDA=ID/ERiemer(a)eskimo.com, on 3/11/98 3:23 PM:
Christy,

For what its worth ...

I've seen intermittent internal shorts in printed wiring boards that were
later found to be
caused by etch defects that had left copper in a ground plane clearance
zone around a via.  The
copper was nearly touching the via land but not quite, and when the board
warmed up there was
enough movement to cause the board to short.

Ed Hare
SEM Lab, Inc.
--

               SEM Lab, Inc.
Scanning Electron Microscopy and Failure Analysis
               Snohomish, WA
               (425)335-4400
   http://www.eskimo.com/~eriemer/SEMLab.htm

Christy Graham wrote:

> TechNet,
>
> I was told recently of a printed circuit card assembly that, when the
> assembly is powered up in the morning, the board runs, but that by the
> afternoon, it fails.  Next day, same board, same results.  The engineer
> thinks this problem is due to a "flux short".  Is this possible?
>
> Christy Graham
> [log in to unmask]
>
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