Jim,
In my dark sordid past I had to build two odd numbered MLB's out of
Polyimide(!!) my normal cycle was 90 minutes at 350 F followed by a 4 hour
bake at 425 F. I left the boards in the fixtures normally for the bake so
that the board would not shrink the tooling holes during the 425 F cure
process. To prevent warpage I took the parts out of the oven hot (probably
with asbestos gloves then) and let them cool in racks overnight. the long
slow cure helped these boards stay flat -- even through subsequent
processing. One of these was a three layer, the other was an eleven layer
where the second layer from the top was a solid ground plane.  I have read
the other answers you have received and agree with all of them. the more
symmetrical you can be around the center, the better off you are. However
the navy did not want to hear about a design change so I had to apply the
above trick
Good Luck
Dave
-----Original Message-----
From: James A Larson <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Date: Tuesday, March 24, 1998 8:22 AM
Subject: [TN] Odd Number Layup-warpage


>We currently have a board requirement for a 7 layer board.
>
>The design limits the modification to make it a balanced
>even numbered layup and to rearrange thicknesses.
>
>The cores are
>
>single sided cap with 3/8 oz. CU.
>.0039 core
>
>followed by
>.016  core  3/8 /  3/8 CU
>.016  core  3/8 /  3/8 CU
>.016  core  3/8 /  3/8 CU
>
>Question:  Does anybody have any ideas to help reduce the
>warpage that will occur on this type of layup?
>
>ROR,  Lagging,  Cool Rates, etc.....
>
>
thanks
>
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