Colin,

More importantly than mandating a "tuff" bow and twist requirement ensure you
have a soundly designed board that will be conducive to flatness by having
vertical and horizontal symmetry.  The IPC spec calls out for .075% worst
case (as I recall, and I hope I am not messing up the decimal point), I have
seen even less ALA .05.  You really need a copy of the design and fabrication
spec procured from IPC (and use it, unlike me that didn't have it at finger
tips to check number).  It may be an aggravating question now but with parts
in hand it is down right awful and you should know first hand.  The well
balanced stack up is everything.  Let me know if you would like me to dive
into the gory details.

Boston Brad
781 858 0783

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