Copper trace thickness/width calculation?

[The Magic Rabbit]

I'm making my first copper board. Is there a formula to calculate how thick I should make a track based on the power? Most of it is either 5V or 12V at less than 10mA but there are a few tracks that will be carrying 12V at up to 2A, from the FETs.

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[Farley]

Try this site:
http://www.4pcb.com/trace-width-calculator.html
It has javascript calculators and also shows the formulas used if you scroll down a bit.

[The Magic Rabbit]

Thanks!

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[waspinator]

Try this site:
http://www.4pcb.com/trace-width-calculator.html
It has javascript calculators and also shows the formulas used if you scroll down a bit.

Why does only current matter in the calculations? if I have 30V at 1A it suggest a 30mil trace, or 1V at 30A, isn't the same amount of power dissipated?

[johansen]

Why does only current matter in the calculations? if I have 30V at 1A it suggest a 30mil trace, or 1V at 30A, isn't the same amount of power dissipated?

power loss is resistance times amps squared.

[Kilrah]

P=RI^2.
R depends on your trace, all that's left is current.

Voltage plays no role in the heating part of it.

[Neilm]

Why does only current matter in the calculations? if I have 30V at 1A it suggest a 30mil trace, or 1V at 30A, isn't the same amount of power dissipated?

The track is carrying the same amount of power - it is not dissipating that power. The power that is dissipated is the small voltage drop you will have along that trace. Making the trace wider will reduce the resistance of the trace and hence reduce the voltage drop.

[fubar.gr]

Another very good PCB calculator is Saturn PCB Toolkit: http://www.saturnpcb.com/pcb_toolkit.htm

When specifying trace width you have to take into account

1) what is the max desired temp rise above ambient and
2) what is the max voltage drop you can tolerate

Sometimes the only way to fullfil the above requirements within a specific PCB area will be to either use a heavier copper PCB or add more solder and/or external copper wire.