One other advantage to single ply construction other than lowering cost is flatness enhancement. We have actually seen lower warp and twist with single-ply construction. As long as your board fabricator is using quality material and vacuum assist lamination, single ply construction should not be a problem. Tom Coyle Field Services Engineer HADCO Corporation Marcus, Most people use a minimum 2 ply construction. Some us this a minimum due = to some misconceptions regarding UL requirements. Check your UL file and = determine what the specified minimum dielectric thickness is for the = pre-preg you intend to use. Unless a single ply would not meet the = minimum thickness or a 2 ply minimum is stated in the file notes, I = don't see a problem using a singe ply.=20 The only restriction I can find regarding UL is in UL 796 specification = section 12.8 under electrical insulation. It states that "the total = buildup shall be equivalent to a base material layer with respect to its = electrical relative thermal index." If a single ply meets that = requirement, then it should be acceptable.=20 I would not recommend a single ply for dielectrics below .004". This may = create some electrical problems in the board. For this concern, I would = check with designer of the part.=20 =20 I hope this helps. Ed Cosper Graphic Electronics Inc. Tulsa OK=20 ---------- From: [log in to unmask][SMTP:[log in to unmask]] Sent: Monday, April 28, 1997 6:52 PM To: [log in to unmask] Subject: one prepreg? Hi everyone! I have a question to you about the minimum numbers of prepregs between = two conductive=20 layers. In our standards it is specified a minimum of two prepregs to = secure good=20 reliability. However, in order to reduce cost we would like to use only = one. What kind=20 of drawbacks can I expect? Is there a minimum prepreg thickness or epoxi = content that=20 can be used? Every comment is highly appriciated Thanks in advance,=20 //Markus=20 Markus Gauffin M.Sc. Printed Board Assembly Technology Ericsson Telecom AB e-post: [log in to unmask] *************************************************************************= ** * TechNet mail list is provided as a service by IPC using SmartList = v3.05 * *************************************************************************= ** * To subscribe/unsubscribe send a message <to: [log in to unmask]> = * * with <subject: subscribe/unsubscribe> and no text in the body. = * *************************************************************************= ** * If you are having a problem with the IPC TechNet forum please contact = * * Dmitriy Sklyar at 847-509-9700 ext. 311 or email at [log in to unmask] = * *************************************************************************= ** *************************************************************************** * TechNet mail list is provided as a service by IPC using SmartList v3.05 * *************************************************************************** * To subscribe/unsubscribe send a message <to: [log in to unmask]> * * with <subject: subscribe/unsubscribe> and no text in the body. * *************************************************************************** * If you are having a problem with the IPC TechNet forum please contact * * Dmitriy Sklyar at 847-509-9700 ext. 311 or email at [log in to unmask] * *************************************************************************** *************************************************************************** * TechNet mail list is provided as a service by IPC using SmartList v3.05 * *************************************************************************** * To subscribe/unsubscribe send a message <to: [log in to unmask]> * * with <subject: subscribe/unsubscribe> and no text in the body. * *************************************************************************** * If you are having a problem with the IPC TechNet forum please contact * * Dmitriy Sklyar at 847-509-9700 ext. 311 or email at [log in to unmask] * ***************************************************************************