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 -----------------------------------------------------