In your message dated Friday 13, September 1996 you wrote :
> We are looking for help to save some 4 layer boards that have a slight but
> unacceptable warp. The
> warp occured when the books were taken apart too soon after lamination.  We
> looked at the construction and the layout and ruled them out as to
> contributing to the problem.
>They did not have a proper cool down cycle. 
>Does anyone know of a way to get rid of the warpage?
>These parts are 12" x 9" x .062"
> 
> Thanks again,
> Jim Moritz
Jim

If this is really thermally induced bow you can easily flatten them by baking in 
an oven on a flat steel plate at 150C (300F). Use a weighted panel on top of a 
stack of 10 circuits to keep them flat during the bake. The boards need to reach 
this temperature and held for at least 30 minutes before allowing to cool 
naturally. Thermal stress is normally characterised by a dishing of the panel, 
i.e. bow is the same in the x and y axes. It is a little more difficult if they 
have been drilled and plated but still possible to get them within acceptance 
limits.

If the bow is caused by crossed warps in the pre-preg and inner layer laminate 
then you will not be able to flatten them. This is characterised by a bow in one 
direction in the x-axis, with an opposite bow in the y-axis.

Good luck
-- 
Paul Gould
EMail [log in to unmask]

***************************************************************************
* TechNet mail list is provided as a service by IPC using SmartList v3.05 *
***************************************************************************
* To unsubscribe from this list at any time, send a message to:           *
* [log in to unmask] with <subject: unsubscribe> and no text.        *
***************************************************************************