I found myself needing to attach small heatsinks to Mosfets and CC power regulators. Also some high-power diodes.
Today I have learnt that thermal compounds, even best in the market, are dozens of times less conductive than aluminium or copper.
I understand thermal compound is used only to cover microscopic cracks.
But what about thermal adhesive tapes?
My question is:
Using a thermal tape, I might completely cover the surface between the heat source and the heat sink in order to join them together.
If thermal tape is 100 times less conductive than aluminium, how do they manage to do their job and transfer the heat even at high power applications?
Best Answer
The total thermal resistance is the length * resistivity / Ac, where length is the length of the conductive path, Ac is the cross-sectional area of the conductive path, and resistivity is the thermal resistivity of the pad.
The conductive path length is actually just the thickness of the pad. So even though the resistivity may be high, because the thickness of the pad is very small, it is an OK thermal conductor overall.
It is a design goal to make the pads out of the best all around material. It is hard to find anything conformable that can act as a heat sink pad that is extremely conductive like copper or aluminum. Sometimes the pads also need to provide electrical insulation.