I have watched the various responses to this question, and basically the
problem is it is a BAD design. board layouts should always be as symmetrical
as possible in terms of construction and copper fill. The issue of crossed
ply glass may indeed be the case. It is most likely to be found in the 28mil
core which will be constructed of 4 plies of 7628 glass. The behaviour of
this particular dummy core will dominate the behaviour of the whole package,
and the material should be looked at in isolation before looking at anything
else. There is no mention of the copper distribution or thickness, which may
also cause the problem if all the planes are concentrated in one area
(vertical or horizontal). The control of heat up and cool down in the press
may alleviate some of the issues of flatness later, but essentially the
design would naturally bend like a banana due to that huge dummy core.
Dougal Stewart

email:  [log in to unmask]
phone: +44 1896 822204
mob:    +44 7984 629667
www.pwbsolutions.co.uk
----- Original Message -----
From: <[log in to unmask]>
To: <[log in to unmask]>
Sent: Wednesday, April 23, 2003 8:03 AM
Subject: [TN] Warpage


> Fellow technetters,
>
> I am back with the same old problem: bow & twist
>
> we are producing a 14 layer  , cap lamination board for one of our
customer
>
> the construction is as shown below:
>
> - - - - - - - - - - - - - - - - -  - -
> **************************          3 mil core
> - - - - - - -  - - - - -  - - - - -  -
> ^^^^^^^^^^^^^^^^^^^           1080
> - - - - - - - - - - - - - - -  - - - -
> **************************          28 mil dummy core
> - - - -  - - - -  --  - - - - - - - -
> ^^^^^^^^^^^^^^^^^^^           2116
>  - - - - - - - - - - - - - - - - -  - -
> **************************          3 mil core
> - - - - - - -  - - - - -  - - - - -  -
> ^^^^^^^^^^^^^^^^^^^           1080
> ^^^^^^^^^^^^^^^^^^^           2116
> - - - - - - - - - - - - - - - - -  - -
> **************************          3 mil core
> - - - - - - -  - - - - -  - - - - -  -
> ^^^^^^^^^^^^^^^^^^^           1080
> ^^^^^^^^^^^^^^^^^^^           2116
> - - - - - - - - - - - - - - - - -  - -
> **************************          3 mil core
> - - - - - - -  - - - - -  - - - - -  -
> ^^^^^^^^^^^^^^^^^^^           1080
> ^^^^^^^^^^^^^^^^^^^           2116
> - - - - - - - - - - - - - - - - -  - -
> **************************          3 mil core
> - - - - - - -  - - - - -  - - - - -  -
> ^^^^^^^^^^^^^^^^^^^           1080
> ^^^^^^^^^^^^^^^^^^^           2116
> - - - - - - - - - - - - - - - - -  - -
> **************************          3 mil core
> - - - - - - -  - - - - -  - - - - -  -
> ^^^^^^^^^^^^^^^^^^^           1080
> ^^^^^^^^^^^^^^^^^^^           2116
> - - - - - - - - - - - - - - - - -  - -
> **************************          3 mil core
> - - - - - - -  - - - - -  - - - - -  -
>
> Obviously, we are getting warpage in boards
> the construction is customer given and he is not ready to change this
>
> Are there any solutions to avoid warp in these boars
>
> cheers,
> Madhu
>
>
>
>
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