What will be the role of a copper layer in a metal core PCB in thermal dissipation?

In the design of a power electronic PCB, I want to use a metal PCB for heat dissipation of a TO-220 package MOSFET. To do that I want to mount metal PCB on the MOSFET with the use of thermal paste and screw exactly like we do when we use heatsink for the same package. Should I leave the copper of PCB between MOSFET surface and dielectric of PCB or remove the copper surface and leave only the dielectric opening?

PCB Design, PCB Materials
December 5, 2023

I doubt it makes much difference unless the copper extends beyond the contact that would exist with the dielectric.

If the copper extends, you’ll have better lateral heat spreading and that will conduct through the dielectric so there will be less temperature drop across the dielectric.

Copper conducts heat about 400x better than the dielectric (which may be 50-200um thick) and is typically 35 or 70um thick (1oz/2oz). So extending it at least a few mm should help a little. I’m not sure it’s a huge difference, even at 200um and 1.0 W/m*K the temperature drop at (say) 5W is less than 7°C if I did the sums correctly (10mm x 15mm contact). If a 15 x 20mm pad was isothermal (which it won’t be but say it was a bit bigger than that), then it would reduce the drop to half, saving a few °C. The savings would be proportionally less (or worse) if the dielectric was thinner, so it might not be much.

Oliver Smith

Oliver is an experienced electronics engineer skilled in PCB design, analog circuits, embedded systems, and prototyping. His deep knowledge spans schematic capture, firmware coding, simulation, layout, testing, and troubleshooting. Oliver excels at taking projects from concept to mass production using his electrical design talents and mechanical aptitude.

Oliver Smith

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