:: PCB copper current loading

general relation of current loading for PCB (based on IPC-2221, aka IPC-D-275/MIL-STD-275)

Width = (Current[Amps]/(k * (Temp_Rise[deg. C])b))(1/c))/ Thickness , in mils
(for multilayer) internal layers: k = 0.024, b = 0.44, c = 0.725
(top/bottom side) external layers: k = 0.048, b = 0.44, c = 0.725

for common copper clad PCBs, each ounce copper grade PCB clad is suppose to give a thickness of 1.37mils. However, as we all know all sellers boasts that their boards are of the standard cladding, nobody could really tell if that 1 ounce PCB was really truly fully done up with 1.37mils. so based on PCB product standard uncertainties, i will round down the thickness to 1.3mils and tabulate the below table based on a 10 degree celcius temperature rise. tracks widths required are the numbers in RED.
 
PCB oz. mils (thick) 1A 2A 5A 10A
1 1.3 12.5 32.6 115.4 300
2 2.6 6.2 16.3 57.7 150.1
3 3.9 4.2 10.9 38.5 100.1
4 5.2 3.1 8.2 28.9 75.1

based on the above, it would be good to consider using bridging wires to carry extra current capacity where copper space is limited. this is a very nice resource list from ALTERA, on additional aspects of complexities of powering and PCB plane couplings (http://www.altera.com/technology/signal/board-design-guidelines/sgl-bdg-index.html)

as temperature rises, resistance increases, so it can be quite a domino effect if heat dissipation has not been considered carefully in high power situations. based on 60 degree celcius derating of cables (PVC jacket), even small cables can add a ton of additional current loading when compared to tiny 10mil PCB tracks.
AWG Diameter / mm max amps
30 0.25 0.5
28 0.32 0.8
26 0.4 1.3
24 0.51 2.1
22 0.64 5
20 0.81 7.5
18 1.02 10
16 1.29 13
14 1.63 17
12 2.05 23
commonly used PCB jump wires are AWG18-24. slapping on AWG18, saves much of copper "real estate" hands down.

however at high frequencies, skin effect happens. (http://en.wikipedia.org/wiki/Skin_effect) very very cool physics in that, it is also why inductive cookers are possible.

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