Ok Guys,

I've read an  abundance of responses regarding technical possibilities.
However, I would like to submit a probability.  Ask you board shop if they
Hi-pot high resistance shorts.  Some time ago it was common to hi pot a high
resistance short. These are boards that repeatedly fail test but probing
with a standard ohm meter does not show any conductivity.  A long time ago,
in a place far far away, we used to simply take a hi pot and blast the damn
thing out. Then it would pass test.  What we were dealing with was a very
small fine line ( typically less than .001 ) short or what I call copper
dust. This is where the etcher leaves fine copper particles embedded in the
glass. It takes on the appearance of copper dust when you see it.

Over time we learned that hi potting out shorts was not a good thing.
Someone technical and a lot smarting than I pointed out that the current
would carbonize the small amount of copper inside the board and leave a
"track" for potential future shorting. Although the board would not pass and
immediate retest, I would think a reliability issue would remain .  In any
case, I do believe this is still fairly common practice among many shops.
Especially when you just need that one board to make the order. Perhaps you
are dealing with a board that failed test initially and has been "reworked"
with a hi pot.


Just my thoughts...

Ed Cosper
Director Quality Assurance and Engineering
American Board Company.

----- Original Message -----
From: Jon Moore <[log in to unmask]>
To: <[log in to unmask]>
Sent: Friday, September 10, 1999 8:04 PM
Subject: Re: [TN] Internal fab shorts that happen over time...


> Steve,
>      My first place to try would be Robisan Labs.  Call them at
317-353-6249
>
> Jon Moore
>
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