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If a trace can carry 3A for a temperature rise of 20°C, will adding forced air over the board increase current capability (by any factor)?

Is the current limit defined by the heat or is it the properties of the material (geometry, type, etc..)?

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  • \$\begingroup\$ If heat is the only problem, forced air will help. But often the voltage drop is a bigger problem (not enough voltage at the other end, or compromised measurement accuracy, audio distortion, etc). A thick wire soldered in parallel can solve this - and reduce heat creation too. \$\endgroup\$ – Brian Drummond Dec 18 '14 at 21:17
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Yes (forced air increases current capacity), and yes (the current limit is due to power dissipation).

Note that this is from the board house point of view. From the EE point of view, voltage drop across a trace can also be important. Air cooling doesn't do much for that.

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I'm going to throw in my $0.02 and say that increased temp => higher resistance => higher voltage drop, and correspondingly cooling (via airflow or any other mechanism) should result in a lower resistance and therefore either less voltage drop or higher current capacity.

I initially thought that the difference would be trivial, but according to a quick google search - [sarcasm]100% guaranteed to be correct![/sarcasm] - changing temp from 40C to 20C should reduce copper resistance by ~8%. That's not huge, but if true then it's way too large to be ignored either.

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  • \$\begingroup\$ As a first guesstimate of copper/ metal resistance (near room temp.. not too much colder.) I just guess it's proportional to the absolute temperature, so 20 out of 300, 8% seems reasonable. \$\endgroup\$ – George Herold Dec 19 '14 at 3:21

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