:: 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.