Quite a lil thread here...

Material will do what it wants... its just a case of when.  If the design was
good and the board still warped I would speculate an odd thickness driving
the fabricator to build the double sided part with Cu foils and pregs.  This
could introduce twist or bow relative to grain.  If it is a standard double
sided build, that is a double sided copper clad laminate or C-stage then it
won't warp.  The suppliers of laminate supply this material by the linear
mile or miles.
I have yet to see a warped board that wasn't attributed to the design or
possibly Operator Error, in which case they wouldn't get shipped.  In the
case of "bad design" where the Customer will not revise then it is only a
matter of time before you walk away from the job.  You can only relate the
facts arrived from working hard and being honest.  Well, that's my warped
perspective....

Brad

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