How to design a PCB for sourcing 200A to MOSFETs
A better question would be &quot;How do I get the heat out of the package&quot;
But the PCB also makes a difference because the heat has to go somewhere or things continually get hot.
Many of them are package limited, but it really boils down to power, the packages can't take the power and if continuous current was used, it would probably melt the package. This fet can handle 400A of current pulses, but the designer must keep the average power and temperature low.

Source: https://www.ti.com/lit/ds/symlink/csd18512q5b.pdf?HQS=dis-dk-null-digikeymode-dsf-pf-null-wwe&amp;ts=1611874884504
In the same datasheet, they give a layout and a thermal resistance number (which is really nice). This one 125C/W this means that 1W of power would raise the package temp 125C (which is close to the limit). Rdson is 3mΩ so sqrt(1W/3mΩ)= 18A

This one 50C/W this means that 2W of power would raise the package temp 50C (which is close to the limit). Rdson is 3mΩ so sqrt(2W/3mΩ)= 25A

If you wanted to get the power higher you would need a heatsink on the package.