Couldn't lurk any more.

There's one other item that is often overlooked.  One should check out the
panel racking fixtures used in the Fab shop.  Often the panels are racked
standing on their edges at a small angle from vertical for solder mask final
cure.  More than once, I've seen panels develop a warp during higher
temperature processing due to heat and gravity.  Bend the boards straight,
and they still have a memory of their previous shape.

This isn't often seen with multilayers because of the added stiffness of the
inner layer planes and the use of higher Tg materials.

Don Vischulis

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