The old MIL-STD-275E spec page 34 and 36 has charts in it that give you a guide that is de-rated based on the Military standards. http://www.dscc.dla.mil/Downloads/MilSpec/Docs/MIL-STD-275/std275.pdf The IPC has the same charts in IPC2221 page 38. According to what I have heard, these charts are approximately 50% de-rated... and based upon phenolic material. There is some impressive work being done by Thermalman that gives more realistic numbers to a thermal design. http://www.thermalman.com/ If you want to use a free online calculator there's one developed by Brad Suppanz at http://www.geocities.com/CapeCanaveral/Lab/9643/TraceWidth.htm Best Regards, Bill Brooks PCB Design Engineer , C.I.D., C.I.I. Tel: (760)597-1500 Ext 3772 Fax: (760)597-1510 -----Original Message----- From: [log in to unmask] [mailto:[log in to unmask]] Sent: Tuesday, May 11, 2004 3:15 PM To: [log in to unmask] Subject: [TN] Formula Although I know it's been discussed numerous times, my search in the archives is coming up empty. Is there a formula that gives the relation between trace width-length and the current it is able to carry for a given foil weight? Thanks. --------------------------------------------------- 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 -----------------------------------------------------