Gaetan: Here's something I worked out some time ago: Resistance of a Trace --------------------- A) Resistivity (r) of copper @ 20 deg c = 10.37 [(circular mils * ohms) divided by feet] B) The units of resistivity (r) are: circular mils, ohms, feet if : 1 circular mil = 0.78540 square mils then : Resistivity (r) of copper = 10.37 * 0.78540 [(square mils * ohms) divided by feet] = 8.15 [(square mils * ohms) divided by feet] also if : 1 foot = 12 inches (and 1 divided by 12 = .083333...) then : Resistivity (r) of copper = 8.15 * .083 [(square mils * ohms) divided by inches] = 0.679 [(square mils * ohms) per inch] The formula for resistance of a material is: R = r(l/a) where R = resistance in ohms r = resistivity l = length in inches a = cross sectional area of conductor (trace) in square mils So: If an internal trace on a circuit board is .010 inch wide, is one inch long and was etched on 1 oz/sqft (.0014 inch thick) copper clad laminate, then its' resistance is : a = 10 * 1.4 = 14 sq_mils l = 1 R = .679 sq_mil-ohms per inch ( 1 / 14 sq_mils ) = .679 sq_mil-ohms per inch ( .071 in/sq_mils ) = .049 ohms I realize this is English units, so you'll need to adjust, obviously, to metric. Michael Hiteshew Lockheed Martin NE&SS Marine Systems 410-682-1259 -----Original Message----- From: Gaetan Fournier [mailto:[log in to unmask]] Sent: Thursday, December 13, 2001 12:27 PM To: [log in to unmask] Subject: [TN] Trace resistance Does anybody knows a good link or freeware for DC resistive calculation in function with the thickness, width and length of a PCB track. I already know about "trace with calculator" http://www.aracnet.com/cgi-usr/gpatrick/trace.pl but this is not exactly what I'm looking for, current and temperature rises aren't the issues for my application. It's more a question of DC equivalent resistive for a coil made with a long PCB trace. Thanks GF --------------------------------------------------------------------------------- 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 the following message: SET Technet NOMAIL Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail 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 ---------------------------------------------------------------------------------