basically you are trying to bond a fully cured laminate core, that has
already had stress put in during the bonding cycle at the laminators,
with prepreg and copper foil on the side that has had some stress relief
during the etching process. The resin in the prepreg will shrink
somewhat after the temperature during bond has cooled below the material
Tg, and this has the effect of pulling in the edges of laminate which is
basically a rigid structure. If you were to laminate prepreg to both
sides of the core, you even out the 'pull'. If the design on a 4 layer
is good, this 'pull' will not distort the panel at final etch.
Dougal
Dougal Stewart
Product Development Manager
Viasystems Selkirk Ltd
Selkirk, Scotland, TD7 5EJ
Tel: +44 1750 21601
Fax:+44 1750 22513
email [log in to unmask]
> -----Original Message-----
> From: Matthew Sanders [SMTP:[log in to unmask]]
> Sent: Monday, July 06, 1998 8:27 PM
> To: [log in to unmask]
> Subject: Re: [TN] Warpage
>
> Can someone explain why a 3 layer board would warp? It seems that the
> structure would be balanced around the middle if it was 1) ground 2)
> signal
> 3) ground. I don't fully understand why an odd number of layers warps.
>
> Thanks,
> Matt
>
> Matthew Sanders
> PWB Procurement Engineer, Trimble Navigation Limited
> [log in to unmask]
> Phone: (408) 481-7817
> Fax: (408) 481-8590
>
> > -----Original Message-----
> > From: Charles Barker [SMTP:[log in to unmask]]
> > Sent: Saturday, July 04, 1998 9:04 AM
> > To: [log in to unmask]
> > Subject: Re: [TN] Warpage
> >
> > Dear L. Ramesh,
> > Warpage can be caused by many different things. One frequent cause
> that I
> > have run into is poor board design. It is important to keep the
> amount of
> > copper on each layer balanced about the middle of the board when
> viewed
> > from the edge. As an example, a four layer board with plane layer(s)
> > should
> > be:
> >
> > Layer one, signal
> > Layer two, plane layer (Power of Ground)
> > ========================================= Middle of Board
> > Layer three, plane layer (Ground or Power)
> > Layer four, signal
> >
> > If the circuitry NEEDS only ONE plane layer (three layer board),
> duplicate
> > that layer to provide the necessary balance (make it four layers).
> > There should always be an even number of layers in a multi-layer
> board.
> >
> > There can also be other issues such as the grain direction, size and
> > structure of the pre-preg material. One of the board fabricators on
> > TechNet
> > will have to explain those issues to you. Other causes could be how
> the
> > board is cooled after lamination.
> >
> > I hope this helps.
> >
> > Charlie B.
> >
> >
> >
> > Please respond to "TechNet E-Mail Forum." <[log in to unmask]>; Please
> > respond
> > to "L. RAMESH" <[log in to unmask]>
> >
> > To: [log in to unmask]
> > cc: (bcc: Charles Barker/US/I-O INC)
> > Subject: [TN] Warpage
> >
> >
> >
> >
> > Dear Technetters,
> > I would like to know the possible causes for warpage and its
> control. All
> > suggestions is gratefully acknowledged.
> > Regards,
> >
> > L. RAMESH, Tel: +91-8221-26618, 26619,
> > Indal Electronics Ltd., 26375, 26584 Extn: 345
> > No.12 A, Industrial Area, Fax: +91-8221-26641
> > Nanjanagud 571 301, email: [log in to unmask]
> > District Mysore, INDIA. web site:www.indalpcb.com
> >
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