Recommended Heat Sink(s) and/or Fan(s)

Do we have an idea of what are the recommended heatsink and/or fan specs for this board? I have a low profile case and am considering my options.

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If I’m not mistaken, the board comes with heatsinks and a CPU fan; not sure of their dimensions however.

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The Crowdsupply page makes no mention of heatsinks/fans in the “What’s in the Box?” section.

… I have a low profile build I am working out and I am concerned that the height of the heatsink pictured will be too tall for my chasis.

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I’d love to know this for certain too, before ordering cases. It looks like it will fit in 1U…

I am targeting less than 1U — I think I will end up swapping out that heatsink. I can probably guess the heatsink height based off of the M.2 slot dimensions… hrm.

I’m guessing the heatsink is 20mm wide and deep and 30mm tall. I’m pleased to find that tiny heatsinks are abundant so this wont be a problem for me to aquire.

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Parts are subject to change until boards start shipping, so no definitive answer can be given at this time. But it looks like the fans/heatsinks stick up about 3 and a half cm from the top of the board on a preproduction model. That may be too much for a 1U case.

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The offset is likely different, but fwiw the tallest Supermicro heatsinks that still fit in 1U are 27.8mm.

https://www.supermicro.com/en/support/resources/heatsink

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The newly released bill of materials has these heatsinks in it:

also

As far as I can tell, the non-fan heatsink that is the taller heatsink (using the orange clamp, in the pics on crowdsupply) is HS2 and is 32.6 mm height.

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Awesome! I am almost certainly going to need to get a shorter heatsink… Good stuff. Appreciated.

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I think that the K1 fan mounts on top of the HS1 heatsink, which adds up to 29.5mm assuming I read the numbers correctly. So this is probably too high for a 1U box also.

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So – Can I get suggestions on the shallowest heatsink an/or fan I can get for these specified form factors? I am unfamiliar with the clip-on heatsink ecosystem and the stuff I see on these sites that were posted. I am just not sure if the shallower options would fit on the Unmatched.

For example this one seems shorter:

than:

… So if I got the shorter one it would fit and work with the Unmatched?

Would this one be fine?

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You can’t just replace it with a shorter heatsink; passive cooling requires a large heatsink with significant mass and surface area for the application. If you make it shorter, you also have to make the footprint larger if you want to keep it passive, or add a fan to make it active.

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I agree, however i dont know from experience what would work. i def have seen small heatsinks being “enough” without a fan on a cpu that doesnt get hot. I dont mind using a fan either. What i need is heatsink+ fan at 30mm height or less.

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The shorter ones from that Radian company will likely fit fine on the chip. The question is do they cool it enough? Was it over-engineered with an extra large heatsink? Or is it just barely big enough? If you have air flow over it, it makes a big difference. You could put a thermocouple on it with a smaller heatsink and see if it stays in spec. Really the only way to know unless SiFive happens to have some more data.

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Im having trouble understanding what a thermocouple is and how it can be used in this situation. I see things via searching that look like its for measuring temperature. Mind clarifying that? Thank you.

Ya, a thermocouple is just to measure the temperature. You can use any method you want to get the temp. I have a thermocouple on my Fluke multimeter. You could look up the specs of the chip to find out what temp range you need to stay in. Then run the board with the official heatsink and get some temps after running it hard. Then swap out the heatsink and see what temps you get. Note, you can fry the chip if it gets too hot, and they can get real hot very fast (seconds). Also note, the heatsink will be lower temp than the top of the chip surface.

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FYI There is a temporature sensor on the U740 chip, unlike the unleashed. So the linux kernel should be able to monitor the temperature and slow or shut down if it gets too hot. But there is also the other chip (pci bridge?) with a heat sink, I don’t know if that one has a temperature sensor.

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Who would know if it has a temperature sensor? Is there someone I can contact?

The other chip with the heatsink is the PCIe switch, afaict. The chip is the Asmedia ASM2824, so you may be able to look it up in it’s data sheet.

Edit: I hunted around, this part isn’t in the common places like Digikey, Mouser, Octopart, or even the more obscure ones. The Asmedia site doesn’t have a data sheet as far as I can tell. The component is a few years old, but not ancient. You’d probably have to write the company directly and request the data sheet unless you can find it buried somewhere.

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They also have INM21001-28W/2.6, which is 27.6mm tall. You probably want the tallest one you can get that will still work.

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