I agree with Bob moisture is the most likely reason for the delamination.
Polyimide laminate is more susceptible to moisture absorption than epoxy
laminates by a factor of 4.
The inner layers should be baked to remove moisture and the pre-preg should
be stored in a dessicator prior to bonding the board.

However depending on where the delam is there may be other reasons
Is the delamination between the pre-preg and the oxide(?) surface in which
case a poor or patchy oxide finish may be the reason, or is the delam
between layers of pre-preg and foil, in which case inadequate cure
temperature or time may be the cause.
hope this helps
geoff layhe
www.lamar-uk.co.uk


> ----------
> From:         Chuck Brummer[SMTP:[log in to unmask]]
> Reply To:     TechNet E-Mail Forum.;Chuck Brummer
> Sent:         09 February 2000 21:30
> To:   [log in to unmask]
> Subject:      Re: [TN] Delamination
>
> 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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