Bob gets my vote for best possibility.  Moisture, residual or added by an operator, is
the best possible answer for on large delamination.

Is there a ground plane behind the blister?  Sometimes just a whole lotta heat in one
place can cause a failure too.

Chuck Brummer
Acuson

Bob Dube wrote:

> Sounds like residual moisture or some other volatile in the board.
>
> Bob Dube
>
> -----Original Message-----
> From: Stephen R. Gregory <[log in to unmask]>
> To: [log in to unmask] <[log in to unmask]>
> Date: Wednesday, February 09, 2000 12:15 PM
> Subject: [TN] Delamination
>
> >Hi ya'll!
> >
> >We just finished building a lot of 48-boards through SMT. Out of that 48
> >there was one board that we just discovered a big delamination blister on
> the
> >backside...it's about 1.5" wide and maybe 2.5 - 3" long. There was no
> rework
> >done on the board, and it was reflowed under the same profile in a
> >Conceptronic HVA-70 that the rest of them were...and they don't exhibit any
> >problems. There no sign of overheating at all around the blister, and the
> >silkscreen is nice and bright white...we just have this big blister. What
> >might cause that? The boards are polyimide. We didn't bake them, and they
> >were real fresh boards date code was 0300. Like I said, it was the only
> board
> >that had a problem...the rest are fine.
> >
> >TIA
> >
> >-Steve Gregory-
> >
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