I am trying to specify the stackup for a controlled impedance psudo-VME backplane. This backplane has controlled impedance traces of 100 Ohms and 50 Ohms. The current finished board thickness is 0.093" and consists of ten layers, 4 of which are controlled impedance layers. In discussion with a local fab shop I am finding that in order to create 100 Ohm traces, the width of the dielectric (for FR-4) is prohibitive. The only alternatives are to cut back on the number of layers or substantially increase the PWB thickness (which causes a large headache in finding components with sufficient lead length). I have two questions concerning this and I hope someone out there can help: a.) Are there any major drawbacks to producing a backplane with, say, 4 layers only? i.e. Is there a limitation on the minimum number of layers for a backplane PWB that I don't know about? b.) How are standard 0.093" OTS VME backplanes produced? They seem to me to have a fair number of layers without resorting to thick PWBs or superfine traces. I hope that someone out there has had experience with this kind of PWB and can help me. Thanks in advance, -- Max.P.Harris Hardware Design Engineer Lockheed Martin Canada, Inc. 'Nil illegitime carborundum' *************************************************************************** * 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] * *************************************************************************** [log in to unmask] [log in to unmask] (Only addresses below this line can be automatically removed) [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask] [log in to unmask]
