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Shortcomings of the IPC-2221 Current Capacity Guidelines October 31, 2006

Our friends at Flomerics have posted an interesting article [1] that describes some of the shortcomings of the IPC-2221 design rule for determining the current carrying capacity of PCB traces. The article concludes that the IPC rule is based only on a 1.6 mm thick, 2-sided FR4 board with a single trace on one side, solid copper on the back side, and 35 um of copper sheet thickness. Modern PCBs can typically have a lot more layers and more copper, and thus be able to take more current with less temperature rise in the traces due to better heat spreading and better heat shedding. The author then derives a new series of graphs showing the temperature rise vs. current and trace width for various PCB stack-ups. Also, it seems that internal layers can handle a lot more current than IPC-2221 would have us think.

[1] New Correlations Between Electrical Current and Temperature Rise in PCB Traces, Johannes Adam