Steve, Try the website for Rogers, they have an impedance calculator. www.rogers.com. -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Mcmaster, Michael Sent: Friday, March 18, 2005 4:56 PM To: [log in to unmask] Subject: Re: [TN] Impedance calculations In addition to possible calculation errors, you also need to be concerned with measurement error. Most TDR techniques calibrate at 50 Ohms, you are trying to measure half of that. Measurement speed can also be more critical. Since the coax line connecting the DUT to the scope is 50 Ohms, if you don't measure at high enough speed or with a long enough transmission line, you will see a shift towards the cable impedance. -----Original Message----- From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Kelly Sent: Friday, March 18, 2005 3:23 PM To: [log in to unmask] Subject: [TN] Impedance calculations Good late Friday afternoon to all, I am trying to understand what happens to my impedance calculations when we start going below 35 ohms. When I use Ultracad or do the calculations by hand I get the following results: Copper finished - .0014 (1 oz.) Dk - 3.5 (it is a flex) h- .003 Line width to get 25 ohms (surface microstrip) - .007 to .008. We wound up building this part with a line width of .016 and the TDR results measured by both myself and my customer are 29-30 ohms. When I use the calculator from Txline it says the line width should be .016. Thanks in advance. Regards Steve Kelly PFC Flexible Circuits Limited Ph: (416) 750-8433 Fax: (416) 750-0016 Cell: (416) 577-8433 E-Mail: [log in to unmask] --------------------------------------------------- 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 ----------------------------------------------------- --------------------------------------------------- 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 ----------------------------------------------------- --------------------------------------------------- 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 -----------------------------------------------------