I think Valerie had the best answer, so far: also, and probably most important, trace resistance can be increased locally by nicks, dishdowns, local reductions (like to get past a too-close pad), fine fractures in the copper trace from handling..... With lighter copper weights becoming standard (1 oz is the standard we spec for our boards, but I hear that is now heavy, and 1/2 oz is standard), nicks and scratches are most likely the biggest concern, or too narrow traces. Especially if any significant DC power is running thru those traces. You might develop hot spots in the board. -----Original Message----- From: Don Vischulis [mailto:[log in to unmask]] Sent: April 12, 2002 9:49 AM To: [log in to unmask] Subject: [TN] Interesting question Techies: I received the following email today, and it aroused my curiosity. What reasons exist for specifying dc track resistance when minimum resistance is governed by a combination of copper weight and design width, and track length? Is this a case of over zealous specification or is there a purpose behind adding another test requirement to a product with extensive specifications? Don Vischulis Original message: You may be able to help me, as I would like to know why - in addition to specifying impedance - an increasing number of PCB designers and PCB fabricators are also specifying DC resistance of PCB tracks? I have had an increasing number of clients ask me about series resistance being specified on PCB tracks, but no one seems to know why.. If you are able to help with some of the reasons why, I would very much appreciate hearing from you. Kind regards Martyn Gaudion www.polarinstruments.com ---------------------------------------------------------------------------- ----- Technet Mail List provided as a free service by IPC using LISTSERV 1.8d 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 delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL 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/html/forum.htm for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ---------------------------------------------------------------------------- ----- --------------------------------------------------------------------------------- Technet Mail List provided as a free service by IPC using LISTSERV 1.8d 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 delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL 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/html/forum.htm for additional information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315 ---------------------------------------------------------------------------------