Hey techies, I have three questions for all you PCB technology guru's out there. 1) First of all, I was provided (in a PCB technology training seminar) the following information: Because of the way the laminate material is made (it follows the textile industry equipment), there is always more yarn (glass fibers) in the warp direction, then in the fill direction. Because of this you will have a more stable board in one direction then the other. When running the smaller size panels (12" X 36") a lay-up called a "cross-ply layup" of the pre-preg material would make the board more stable, and less likely to have warping issues. Can anyone tell me if this is correct or not? 2) I was also informed of the following information: The warping of the boards will never go away, especially by running the boards through more thermal cycles. This will only make it worse. The Epoxy in the laminate material continues to cross link and with each thermal cycle the epoxy cross links more and more. This means everytime you run the board through an oven you lose some of its ductility. The board is in its relaxed state while in the warped state, and trying to flatten the board out during a heating process will cause even more problems, because as soon as the board is heated up again it will go back to its relaxed (or warped) state again. Usually the warping of the board is caused by the following problems: 1) Bad design -- uneven stack up of the layers 2) The PCB house did not use the same Pre-Preg (stage B) laminate material as the Cored (stage C) material. Can anyone tell me if this is correct or not? 3) Can anyone tell me what the other causes for warping of a PCB are? As always, thanks in advance for your feedback! Kind Regards, Kathy Palumbo Manufacturing Engineer IPC Certified Instructor Viking Components, Inc. 30200 Ave. De Las Banderas Rancho Santa Margarita, Ca. 92688 BUS: (949) 643-7255 ext. 352 Fax: (949) 459-5360 CELL: (949) 422-4145 E-Mail: [log in to unmask] Web: http//www.vikingcomponents.com/ ############################################################## TechNet Mail List 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://www.ipc.org/html/forum.htm) for additional information. If you need assistance - contact Gayatri Sardeshpande at [log in to unmask] or 847-509-9700 ext.5365 ##############################################################