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Comment by Causality1 | Hacker News Reader

Always been fascinating to me that we only bolt a heat sink onto one side of the board. Nobody's come up with a circuit board material that's electrically insulating but thermally conductive so we could sink an appreciable amount of heat out of the back side?

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Interestingly, thermal and electrical conductivity is highly correlated. You don't see a lot of materials that conduct heat well but behave as good electrical insulators, or vice versa. Both mechanisms benefit strongly from the availability of highly-mobile electrons, which is another way of saying "metal."

> Nobody's come up with a circuit board material that's electrically insulating but thermally conductive so we could sink an appreciable amount of heat out of the back side?

In applications like high-power LED lights, you'll often get 'Insulated Metal Substrate' PCBs where the printed circuit is on an aluminium or copper board, separated by a very thin electrically insulating layer. [1]

However, this has a few downsides: The electrically insulating layers aren't perfectly thermally conductive, meaning a directly attached heatsink will usually perform better; if you make a complex board with 8+ layers of copper (like a modern motherboard) you end up with 8+ layers of insulation; and it's nigh-impossible to use through-hole components.

For LED lighting those are non-issues and, a top-mounted heatsink wasn't an option anyway.

[1] https://dm.henkel-dam.com/is/content/henkel/Bergquist%20Comp...

Oh, that is in fact an important heat path on all but the most intensive components. But with high power components, the heat flux is pretty insane. You can move a huge amount of heat with heat pipes, and it's just easier to move heat out the back.

I put a fairly large/flat heatsink on the back metal of the heatsink support bracket on my intel (overclocked) desktop a few years back it pulled the temps down a couple degrees when a fan was blowing at it under moderate load.

I've been thinking about this for my ryzen lately too, since it appears keeping the top of the die cool is unusually challenging. A lot of mobile/etc parts use the PCB ground plane as a heatsink, so it makes sense that if you can attach a larger heatsink to the back of a normal PC board you should be able to pull heat out of both sides. Particularly in a water cooled system where the top of the heat spreader is remaining fairly cool but the surrounding board is heating up (like my ryzen).

There are in fact thermal PCBs (a.k.a. MCPCB) used for LEDs and other electronics that need to dissipate heat. They have an aluminum or copper layer that supplies rigidity and a heat path out the backside or center of a PCB.

Yeah especially with something like the Pi, you could effectively double the core count by slapping another chip on the other side and add another heatsink.

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