We use the following: 0.25 oz - same top to bottom 0.35 oz - same top to bottom 0.5 oz - same top to bottom 1.0 oz - .0075" smaller top than bottom 2.0 oz - .0015" smaller top than bottom 3.0 oz - .0020" smaller top than bottom The line calculation that our model uses is ((B-T)/2)+T Where T=Top and B=Bottom Jeffrey Bush Director, Quality Assurance and Technical Support 76 Technology Drive - POB 1890 Brattleboro, Vermont 05302-1890 Tel. 802.257.4571.21 Fax. 802.257.0011 [log in to unmask] http://www.vtcircuits.com -----Original Message----- From: Mark Larson [mailto:[log in to unmask]] Sent: Monday, May 03, 2004 12:05 PM To: [log in to unmask] Subject: [TN] impedance calculation Hi, when doing an impedance calculation of a trace more accurate results come from using the trapizoidal shape of the trace cross section rather than a square one, is there a rule of thumb people use for what the top width of the trace is in relation to the base? obviously this will be based on the copper thickness. Since it is such a small variable, is there ever a situation where it is really important? --------------------------------------------------- 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 -----------------------------------------------------