>From: John Parsons <[log in to unmask]> >Reply-To: "TechNet E-Mail Forum." <[log in to unmask]>, John >Parsons <[log in to unmask]> >To: [log in to unmask] >Subject: [TN] FAB - Controlled Capacitance >Date: Thu, 31 Oct 2002 11:39:38 -0800 > >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. From the distance between the planes, and the dielectric constant of the PCB material, you can calculate the capacitance using the appropriate formula, which I've forgotten. 8-( Leon -- Leon Heller, G1HSM Tel: +44 1424 14790 Email:[log in to unmask] My web page: http://www.geocities.com/leon_heller _________________________________________________________________ Internet access plans that fit your lifestyle -- join MSN. http://resourcecenter.msn.com/access/plans/default.asp --------------------------------------------------- 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 -----------------------------------------------------