Jim Assuming your geometries are correct (line width/thickness and dielectrics) and you have good estimates of what the resin content of the dielectrics are, then I'll give you two hints: What is the rise time of the pulse coming out of the signal generator? What is the effective dielectric constant of the laminate core and cured pre-preg at the knee frequency of this rise time given the resin contents? Feed this back into your calculator and see what happens. Gerry From: Jim Henderson <[log in to unmask]> Reply-To: TechNet E-Mail Forum <[log in to unmask]>, Jim Henderson <[log in to unmask]> To: [log in to unmask] Subject: [TN] impedance testing Date: Tue, 15 Nov 2005 09:28:08 -0500 Hello, If there are any impedance testing gurus out there I have a question for you. We are testing an edge coupled offset strip line coupon. We modeled the stack up to give us 100 ohms differential. When we test the coupon we get around 130 ohms. We have done a microsection of the coupon and modeled the coupon data and Polar says we should have 105 ohms, within tolerance. We had a 4 panel lot and it is consistent across the board. The coupon is constructed correctly. My question is, other than what I am seeing on the microsection should I look for to find the culprit of the high reading? Any help would be great. Jim Henderson Colonial Circuits --------------------------------------------------- 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 847-615-7100 ext.2815 ----------------------------------------------------- _________________________________________________________________ Don’t just search. Find. Check out the new MSN Search! http://search.msn.click-url.com/go/onm00200636ave/direct/01/ --------------------------------------------------- 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 847-615-7100 ext.2815 -----------------------------------------------------