Hi Sergio, The dielectric thickness (H), soldermask thickness (H1), line width top (W) & bottom(W1), spacing (S) & the circuit height (T) all have impact on the impedance. The circuit height includes the base copper+plated copper & the surface finish like HASL, ENIG / electrolytic nickel gold, Silver etc., But the ENIG/electrolytic gold thickness being so small in comparison to the overall copper thickness the impact on the impedance is negligible, especially if you are talking about +/-10% for 50 Ohms or greater impedance values. If you looking for say +/-5% or less or a Rambus design with 28 ohms impedance than the effect of every component above becomes significant. Hope this helps. Thanks, Krishnan -----Original Message----- From: Sergio T. Ruiz [mailto:[log in to unmask]] Sent: Friday, September 19, 2003 12:48 AM To: [log in to unmask] Subject: [TN] controlled impedance.. hey guys... thanks so much for all the great info on this list! i have yet another questions.. i am working on a controlled impedance board with a twist.. the final coating on this board is nickel/gold.. does anyone have any experience as to how this effects the impedance of a trace? off hand, i am going to guess that since you are basically adding just another conductive layer to the build, it shouldn't matter. and, since the thickness of the layer should be negligible in the calculation.. but.. real experience sometimes thwarts my guesses.. thanks! ____ Sergio T. Ruiz technology and MIS Philway Products, Inc. (419) 281-7777 x232 --------------------------------------------------- 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 ----------------------------------------------------- --------------------------------------------------- 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 -----------------------------------------------------