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> Pcb Trace Width, rough calc
Sch3mat1c
Posted: March 04, 2015 03:54 am
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In case you were wondering;
https://www.google.com/search?q=%2820+amps%...0+kelvin+in+mil

20 amps = current to handle
2.4 mil = copper thickness (2 oz, YMMV)
20 nohm.m = resistivity of copper (approx; I think the preferred value is 17 or so, so this is slightly overestimated, but probably realistic at whatever temp rise)
0.0083 W/(in^2*K) = convection dissipation (i.e., the rule of thumb of 150 C/W on 1 in^2)
20 kelvin = desired temp rise

Compare to
http://www.smps.us/pcb-calculator.html
gives Revised = 701 mil, not too bad.

Note that, this is power per side, so you can carry this current on both sides (say + and - traces) and it's fine. If you don't have much or any current flow on the back side, you can carry a little more power density because the convection from the back side, plus thermal resistance of the board, dissipates a little more than the single-face dissipation of 0.0083 W/(in^2*K).

Thinner traces can carry a lot more, especially if widely spaced, and there's an inner layer ground plane underneath which spreads the heat out.

Tim


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