I'm in digest mode, so maybe there has been more recent discussion, but it seems to me you are over-complicating this situation. They've told you to run a 5mil trace over a ground trace that is 5mils over a ground trace, and to keep that pair away from everything else. That is either a microstrip or an imbedded microstrip, (which your Polar calculator DOES have) depending on whether you are running the impedance controlled line on a surface layer or inside. I would consider putting the ground on the outside with the trace underneath for added protection. The only considerations I can see are: 1) My calculator result is closer to 60 ohms, you may want to verify the numbers 2) The ground trace should be wider. We used 3x the trace width at a previous job, something about the field strength and the square of the distance. good luck, hope I'm not helping some guy in India working for $3 an hour who took this job away from me (a former Intel designer) Jack > -----Original Message----- > From: TechNet [mailto:[log in to unmask]] On Behalf Of John Parsons > Sent: Wednesday, November 19, 2003 11:14 AM > To: [log in to unmask] > Subject: [TN] Co-planar Impedance Calculations > > > Greetings all, > > I have a customer who is doing an impedance design for Intel and he has > no previous impedance experience. This is the information I have. > > - double sided board > - target impedance 50ohm > - signal line 5mil wide, spaced 5mil from "ground" trace and this pair > of traces should be spaced a minimum of 20mil from adjacent traces. > > This is what he was given from Intel. I am using an older Polar model > (CITS25 calculator) which does have models for co-planar designs but > from what I can tell they assume that the signal trace is sandwiched > between ground (return lines) on both sides. Is this a correct > interpretation? Is it possible to model the design as described above? > > While we have some experience with controlled impedance I have no > experience with the aforementioned design and could use some assistance. > > Best Regards > John Parsons --------------------------------------------------- Technet Mail List provided as a 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/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 -----------------------------------------------------