Chris,
Is there even copper distribution on the 2 outer layers? How about on the
inner trace layers? If one of your trace layers either internally or
externally is out of balance with it's 'mate', you could be contributing to
the problem. It could have been that the board shop did some kind of rework
that heated the board, and cooled it in a condition that allowed it to warp
(ie solder mask touch up). You didn't mention your dielectric properties,
but of course they should also be balanced.

At 02:23 PM 9/27/99 -0400, Chris Bartkowiak wrote:
>Friends:
>
>I have a 6 layer board that warps.  The R&D group tells me its a
>Manufacturing problem. I'm not so sure.
>
>Details:
>.062" Thick NEMA FR4
>Stack: (Trace/Gnd/Trace/Trace/Power/Trace) w/1/2 oz copper clad.
>R&D group tells me the layers are balanced from the center of the stack
>out.
>
>What should Manufacturing be doing to prevent these boards from
>warping?  Or is the only solution a higher temperature
>FR4 material that adds cost to the board.  Could it be a problem with
>the board house. Please advise.
>
>Regards, Chris
>
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