Maybe somebody at IPC HQ can corroborate this but I've long been under the impression that the venerable IPC-D-275 current handling charts, which came from the Mil standard of the same number, was generated not from a mathematical formula, but from plotting measured temperature rise vs current data on the different widths and weights of traces. Can anybody out there support or refute this statement? AMP has in isolated instances tried to duplicate these measurments and quickly came to the conclusion that "2 OZ copper thickness" statements don't guarantee a well controlled conductor thickness. To do justice to this type of measurement, one would have to verify every test panel as to copper thickness and trace width, such that an accurate cross-section of each tested conductor could be documented. Definitely tedious. If you didn't, you'd have to design a test which included a relativley large sample population to ensure that a "nominal" copper weight and trace width were being used for each measured situation of each variable. VERY tedious. Hence people like myself fall back on the "official" table in IPC-D-275. And that works for most situations. If that chart WAS generated by a formula, I'd think some of us would like to know that some empirical data was measured and analyzed to verify said formula. I'd like to know how or if that was ever done. The above statements are my own thoughts and opinions and do not necessarily reflect those of my employer. Leonard F. Bendiksen AMP Incorporated Test Engineer and PCB/Fixture Designer Americas Regional Laboratories [log in to unmask] (717)780-6493 *************************************************************************** * TechNet mail list is provided as a service by IPC using SmartList v3.05 * *************************************************************************** * To unsubscribe from this list at any time, send a message to: * * [log in to unmask] with <subject: unsubscribe> and no text. * ***************************************************************************