This is a first for us. Our customer has specified "Capacitance between layers 4 and 5, and layers 6 and 7, shall be greater than 250pf per square inch, assuming unperforated planes". Layers 4 5 6 and 7 are all plane layers (ground/voltage pairs each). Now, I understand the concept of capacitance but I have not come across, nor can I seem to source any info telling me how to ensure that we are manufacturing to this specification. I have the IPC-2141 which makes reference to controlled capacitance lines (not planes) but does not seem to provide any useful info from a manufacturing perspective. Can anyone help? Regards John Parsons --------------------------------------------------- Technet Mail List provided as a free service by IPC using LISTSERV 1.8e To unsubscribe, send a message to [log in to unmask] with following text in the BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest Search the archives of previous posts at: http://listserv.ipc.org/archives Please visit IPC web site http://www.ipc.org/html/forum.htm for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 -----------------------------------------------------