We had a single lot of boards that warped both in the X and Y direction after
one reflow cycle( double sided board).  Boards also warped in the initial bake
out before assy.
The board is an 8 layer FR4 (Tg > 175) board with all inner layers 1 oz copper
and the outer layers 1/2 oz plated up to 1.5 oz.  The copper on the layers looks
reasonably matched.  The construction is well balanced.  Since we have only seen
this happen on one lot, we would like to have the PCB tested to find out what
happened.
Our  PCB vendor does not know what happened.  We need to resolve the issue to
insure that we don't see a repeat. Does anyone know where I can have such
testing or
analysis performed?  Thank you.

Best Regards,

Michael Forrester

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