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October 1999

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Date:
Thu, 14 Oct 1999 14:28:11 -0500
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You are now in the driver's seat. You have one clear picture providing an
insight to delamination. Resin starvation may be redefined and insuficient
resin to start with. Using resin poor laminates, core, and prepregs can
cause what you're seeing. Moisture is but a minor consideration only when
resin poor or aged material is used.

To ensure NO delamination occurs, laminate suppliers must be proven capable
of supplying what is specified as resin to glass ratios, as an example.
Board fabricators must be capable of managing their lamination processes -
from supplier qualification to storage to oxide application to press
qualification (parallelism, thermal characteristics, blow breakers, bad
heater elements, vacuum settings, etc.). If all this comes together, with a
good design, no delamination, misregistration, pad lifting, micro voiding,
or other problems will occur - it says somewhere.

It's fine to test laminate and boards using differential scanning
calorimetry and thermo mechanical analyis, and to bake boards til the cows
do whatever they do (in Wisconsin they polute everything), but the truth
starts with the design.

Again DFM/CE wins all battles though the principle is not applied often
enough. Talk all you will about experiences about this and that. If the
design is not right and concurrently proven, delamination (as but one
example) will result.

Delamination is a design, material selection, and process management
problem. Baking ain't the answer. Boards get baked very well, thank you,
during processing. Only the weak need bake.

Earl Moon
----- Original Message -----
From: Gary Camac <[log in to unmask]>
To: <[log in to unmask]>
Sent: Thursday, October 14, 1999 1:10 PM
Subject: Re: [TN] Board Delamination . . . Boards too old?!


> Stephen R. Gregory wrote:
>
> > I still would like to know why I should need to bake them, because I
recieved
> > a few responses at the time I first had the problem that it was probably
a
> > problem with the lamination process (resin starvation or something) that
I
> > was getting the blisters...but for some reason, it seems that baking
them
> > does prevent the blisters.
> >
>
> Steve,
>
> I agree with what you say.  Why do I need a non-value added operation,
like pwb baking,
> added to my processes?  One more que, one more handling and one more
opportunity for
> something to screw up.  When is the baking process initiated? 3 months? 6
months? a
> year?
>
> I have been told by board manufacturers that delams can be caused by resin
starvation;
> not enough time, temperature and/or pressure during pressing, problems
with the oxide
> (it can apparently loose it's tooth if not processed properly), and
moisture
> absorption.  I have had some manufacturers tell to bake after six months
in-house and
> others tell baking would not be necessary.
>
> All of our pwbs are stored in air conditioned areas, where humidity levels
reach 50% RH
> in the worst part of summer and it is always much lower once the heat
kicks on.  And
> yet,  I can have three assemblies out of one hundred delam, when all were
stored in the
> same place for six months or more. Hmmm.  I have had pwbs stored for over
a year in
> these conditions and have never had delams on them during processing.  I
have also had
> delams show up at wave soldering when the units looked just fine after
reflow and
> adhesive cure passes.  It seams like the opportunity to entrap moisture in
inner layers
> is greater during the pwb's manufacture than sitting in my stockroom.
>
>  Don't get me wrong, its not that delams have been a big problem for us.
Over the
> years they have always been rather scattered occurrences. But some have
been costly for
> us and our suppliers, and, of course, you always have the unhappy customer
that is
> waiting for us to ship product (what a food chain).
>
>  I guess I would like to know what the best practice regarding baking.
From replies I
> have read on Technet, SOP (black boot army - standard operating procedure)
is that
> there is no SOP.  Have any studies been done to quantify the level of
humidity and time
> necessary for delams to be created in FR4 pwbs?
>
> Just my experiences,
>
> Gary Camac
>
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