How does the number of PCB layers affect the temperature of the board?

Question

I understand that a PCB with the exact same circuit on a 2-layer board will get hotter than a higher number board: 4-,6-,8-layer boards. But, I have not been able to find the reasoning for this behavior or any studies with numbers comparing the thermal performance of the same design on different layered PCBs. In a generalized question, how dramatically does the number of layers affect the thermal performance of a design?

Assume the only change between the Board A and Board B is the number of layers.

Thanks in advance!

Answer 1

I believe the assumption is that the thickness of the dielectric insulation ( both thermal and electrical) is less with more copper layers. Also, thermal vias would be used to promote thermal conductivity.

Thus it might take 10 layers just to reduce the thermal resistance by 50% by projecting Toshiba's graph.
So you might as well rely on 1 or the 2 outer layers, one which has the hot component that needs 1 sq.in./W of 2 oz 2x sided Cu with thermal vias to limit heat rise around 50'C of the component.

The dielectric is pretty good thermal insulation as well as the plastic case packages so the chip is much hotter than the outer case unless it has the Toshiba dual-layer thermal planes in it. e.g. a TO-92 is 200'C/W chip thermal resistance above ambient.

Answer 2

I understand that a PCB with the exact same circuit on a 2-layer board will get hotter than a higher number board: 4-,6-,8-layer boards. But, I have not been able to find the reasoning for this

Put very simply, more copper layers provide more low-thermal-resistance paths for heat to flow away from the heat sources, so more of the board surface is useful for passing the heat out to the environment.

Answer 3

As the layers increase, the amount of copper increases and it becomes easier for heat to spread. For this reason, more layers give better results in heat dissipation.