I don't need a Christmas miracle . . .the 0.4% I mentioned was 0.4% per degree C temperature change. For my expected 50 degree C change from ambient and self heating, I will get a 20% change in resistance. I can probably cope with an additional 20% ambiguity caused by board geometry and thickness variations. I have found a raw board specification of 10% on the starting copper thickness. Today's questions: 1. What variations can I expect to see (on finished boards) with a standard production specification of 2-oz. Cu ? 2. Are any of "you guys" willing to share success (or failure) stories of your attempts at "board etch Cu for current sense resistors"? Thanks, Carl -----Original Message----- From: Edward Szpruch [mailto:[log in to unmask]] Hi, As far as I remember IPC allow 10% variations in copper thickness.Take into account that 2 oz is unit based on weight while you are describing thickness.Add to this topography of the foil from lamination side, thickness reduction as result of different surface preparation processes - it seems you need X-mass miracle to get to 4% while you are expecting 0.4%. Good luck and Happy New Year Edward > -----Original Message----- > > I have a project that seems to be a good candidate for a current sense > resistor made as a part of the PCB. I am using the free calculator, > PCBTEMP, from the UltraCAD website (http://www.ultracad.com/calc.htm) > for geometry calculations. I need to know the expected variability in > thickness, batch to batch, for the copper foil on 2-oz stock. I can > live with the 0.4% > TC of the Cu, but I need to evaluate all the other variables in my error > budget before I present my proposal. I would appreciate any success (or > horror) stories from people who have (not) used the board copper as a > current sense method. > --------------------------------------------------- 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 -----------------------------------------------------