All too often, PCB traces are laid out for convenience of footprint with little or no consideration of the PCB traces as circuit elements. Capacitance is sometimes considered but resistivity is often assumed low enough to be ignored. A 6″ trace of 1 oz copper carrying 100 mA of current needs to be at least 31 mil wide to keep the trace temperature less than 5°C above ambient with less than 10 mV drop across it. The calculations which relate trace temperature, resistance, voltage drop to physical dimensions is presented.
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