Robert- Sounds like the core is not symmetrical w.r.t the core centerline. Bet you have a lot more Cu on the ground side of core than the signal side (?) Does eyeballing the artwork for these 2 layers confirm this? -Michael Alderete You wrote... ------------------------------ Date: Wed, 16 Sep 1998 17:02:37 -0700 From: Robert Jordan <[log in to unmask]> Subject: Warpage @ Assembly Greetings, I would like to ask for some insight with respect to an assembly process. I am trying to get a handle on why a 4 layer board would warp @ assembly. The panel is really an palletized array of two boards, seperated by a 60 mil gap and attached @ five perforated ponits that join the panels together. The board is manufactured using Allied's FR406. Construction is as follows; 6" x 9" board 9" x 12.1" array .5 oz foil Prepreg 2@7628 & 1@1080 Core .021 1/1 one side is a ground while the other side is circuit related @ approx. 5% coverage Prepreg 2@7628 & 1@1080 .5 oz foil The panels are pattern plated with 1-1.2 mil of copper in the holes LPI SM Taiyo PSR 4000 Entek 106 The panels show no sign of warpage at our package stage/shipping The panels are seeing two conveyorized reflows in a HotAir Unit? I am not sure if I have properly identified the assembly device. It does use hot air and not a solder wave. The first pass thru the reflow involves some resistors, capacitors. There are no high profile components. This is layer 4. There is no sign of warpage after this step. The second pass with major components added resulted in 30% of the arrays warpping ------------------------------ ################################################################ 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's web site (http://www.ipc.org) "On-Line Services" section for additional information. For technical support contact Hugo Scaramuzza at [log in to unmask] or 847-509-9700 ext.312 ################################################################