Hi All, I have a question concerning the layer stack-up of a board that I am designing for an engineer who is concerned about the voltage isolation provided by the pre-preg material between the layers. The design is for a power supply board that will be 4 layers/0.094" thick with 2 oz. copper on all layers and will contain max voltages of 240 VAC. It also must meet certain CE agency guidelines. He feels that the pre-preg material doesn't provide the voltage isolation needed that FR-4 provides. So to maintain certain high voltage clearances, he wants to fabricate the board with 2 double-sided copper clad laminates and use pre-preg between layers 2 & 3. Some other sources tell me that pre-preg contains the same characteristics of FR-4 when cured and thus the cost of the board would be less if 1 double-sided copper clad laminate was used with foil on each of the outside layers and pre-preg being used between layers 1 & 2 and 3 & 4. Is this true and can anyone supply me with technical info comparing FR-4 to pre-preg materials and also help me in understanding the most cost effective way to fabricate this board. He would also like to use more than 2 oz. copper, but I'm told that 2 oz. is more common than 3 oz., so we are making every effort to use 2 oz. unless someone can tell me of a process that is available that will not add too much cost to the board and provide a higher copper content. Any help would be greatly apprreciated. Regards, Bob Walker ################################################################ 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 technical support contact Hugo Scaramuzza at [log in to unmask] or 847-509-9700 ext.312 ################################################################