# PCB design for high currents

Is a 2-layer PCB design good for a 100 A or more current carrying PCB, or should I switch to 4 layers?

The trace lengths are from 20mm to 50mm.

Also, can anyone give some suggestions on it.

• Depends on how wide traces you make. Are you aware of Ohm’s law? Jul 22, 2022 at 7:47
• How long are the traces carrying the current? Is this DC? Jul 22, 2022 at 7:52
• You should think about thick and very thick copper layers instead of 4 layers. Not only 35 or 70 µm copper but 300 µm up to 3 mm copper layers.
– Uwe
Jul 22, 2022 at 10:04
• >Is a 2-layer PCB design good for a 100 A < NO ,that will burn up any trace. Use a BUSBAR. Jul 22, 2022 at 12:17
• I don't think this should have been closed. It was quite obvious what was being asked Jul 22, 2022 at 13:25

Is a 2-layer PCB design good for a 100 A or more current carrying PCB, or should I switch to 4 layers?

The first thing to ask is how much resistance do I need the trace to be:

100A * 5mΩ is 500mV and power 100A^25mΩ =50W (which is a lot of loss)
100A * 0.5mΩ is 50mV and power 100A^2
0.5mΩ =5W
100A * 0.1mΩ is 10mV and power 100A^2*0.1mΩ =1W ( not so bad)

So I'd probably want to design my traces so they have between 0.5mΩ and 0.1Ω of resistance.

It then comes down to space, width and length of conductor and copper weight.

A 500mil 1oz copper trace has 1.2mΩ of resistance so something like that would work.

Or if you needed to go smaller width a 250mil 2oz copper trace has 1.6mΩ of resistance.

It really depends on what you need for resistance and area and the tradeoffs. (the Saturn PCB design PCB toolkit is one of the better calculators)

• Don't 500 mil x 1 Oz and 250 mil x 2 Oz work out to the exact same cross-sectional area? Wouldn't they have the same resistance per unit length? Jul 22, 2022 at 20:01
• I just pulled the numbers from the calculator, but I did notice that. Jul 22, 2022 at 21:30
• Maybe there is a 2nd order effect involved due to plating or undercutting during etch or something. Maybe the 2 oz copper gets more undercut so the resistance is a tad higher and the calculator accounts for that. Jul 22, 2022 at 21:58

There is a tradeoff between copper thickness, trace width, current and temperature.

More detailed explanation here

For the normal 1 ounce copper I have copied in the graph they supplied. You will probably not be able to get your 100A with that. However, you can go up to 10 ounce copper and beyond, depending on manufacturer. So it might be do-able

Assuming 100A continuous, thick wide traces or solder bus bars.

For example, you can consult one of the online calculators such as this one from Advanced Circuits. Here is one example, plug in appropriate numbers for your application:

So (given my assumptions) for an external layer you can use 7mm wide traces if you have 13oz copper. The cost for 5 prototype 100 x 150mm boards from a typical online supplier is around \$600 USD compared to maybe 1/20 of that for 1 or 2 oz. copper so it is not an inexpensive way to go. The minimum trace width/spacing will also be much more than for thinner copper so mixing high density circuitry with power circuitry on the same board will be problematic.