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 > >################################################################ >TechNet E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c >################################################################ >To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body: >To subscribe: SUBSCRIBE TechNet <your full name> >To unsubscribe: SIGNOFF TechNet >################################################################ >Please visit IPC web site (http://jefry.ipc.org/forum.htm) for additional information. >For the technical support contact Dmitriy Sklyar at [log in to unmask] or 847-509-9700 ext.311 >################################################################ > ################################################################ TechNet E-Mail Forum provided as a free service by IPC using LISTSERV 1.8c ################################################################ To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body: To subscribe: SUBSCRIBE TechNet <your full name> To unsubscribe: SIGNOFF TechNet ################################################################ Please visit IPC web site (http://jefry.ipc.org/forum.htm) for additional information. For the technical support contact Dmitriy Sklyar at [log in to unmask] or 847-509-9700 ext.311 ################################################################