Can you recomend a passiv cooling device like the the one shipped with Rock 5B?
Where to order?
Regards
Passiv cooling device for orion
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The blue passive heatsink on Rock 5B You mention is too weak for Orion.
As the TDP of CD8081 is about 30W, I guess a 1U aluminium heatsink would suffice for decent cooling in a ventilated case. At least I used such a solution for my Rock 5 ITX and official dimensions seem the same for both boards: 84x84 mm overall size with 75x75 mm for holes, but RK3588 chip draws less power (about 15 W).
Here is my choice for Rock 5 ITX in a Factal Design Node 304 with a very low maximum temperature of the SoC under load:
It perfectly fits on Rock 5 ITX and I think this heatsink would also fit on Orion even if footprint is 85x85 instead of 84x84, but the memory chips will require taller pads for contact.
As most of us received the Orion with the mounted 8420B active cooler (preorder), I may keep this cheap solution for the moment, but if I can, I would choose a copper heatsink instead for passive cooling, maybe this one:
However, be aware that I did not test and that the backplate and/or the heatsink might not fit out-of-the-box on Orion! Footprint is 88x88 mm instead of 84x84 mm… So, please only consider this option if You don’t mind adapting/cutting the heatsink.
I got this one:
https://streacom.com/products/fc8-fanless-mini-itx-case/
One single-slot, low-profile PCIe slot (network/ low-power RX 6300 GPU), passive heat-pipe CPU cooling.
I ordered the copper version. I’ll tell you if I can install it without problem. From what I measured it should fit very tightly, if it fits 
Received the copper heatsink. It’ s a perfect fit. I am going to test it under load to see how well it keeps it cool.
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Glad to hear that it is a perfect fit. Looking forward to your update on the test.
I initially left it passive but I changed my mind. The tempeature under load were stabilizing around 80°C but once reached the cool down was very very long. too long imo. the copper block weighs around 400 grams so it has a lot of inertia. hence it is long to heat it up and even longer to cool down. Eventually, I added some thermal pads on the ram chips and installed a Noctua NF-B9 with a power limiter to keep it quiet. I found that the copper fins are very close to each other and the air tends to get stuck in between so you have to force it through somehow. With this config, temperatures of everything on the board never go over 40-45°C.
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Thanks for an informative update. It’s just too bad that your passive cooling doesn’t work for the board. Anyway thanks again.
honestly it was to be expected. The size of the passive coolers of the Steacom FC8 or DB4 Are way bigger and are designed for 45-65W thermal transfer. I am not surprised that this little 400gram block of copper has hard time to fully cool the 35-40W of the SoC.
however, the interesting part here is that this is a very effective cooler once you push air through it, and it is wide enough to cool the ram using thermal pads.
IMO this config looks somehow gorgeous and very silent.
Good to see that the heatsink fits successfully. Indeed, some air flow is always welcome. You are right, pure passive cooling requires sufficient spacing between fins, they have to be tall enough and, very important, an open space above is required to allow natural convection.
In your case, before You installed the fan, the plexiglas seems to entirely cover the heatsink, which is very bad of course…
As mentioned, I will probably test this heatsink as well, but in a closed case with two low speed 120mm fans at front (intake) and back (exhaust). In case of failure, the Radxa solution is bad, as the heatsink is not supposed to draw the full TDP by itself while this copper heatsink is almost perfect for the purpose, either in an open casing or in a closed case with redundant fans.
Your assumption is incorrect for one reason : The temperatures were still high without the plexiglas. One more thing is that I hoped that putting the heatsink in contact with the plexiglas would force a venturi effect between the fins due to convection, but the fins are too close and too straight and long to actually trigger such an effect.
I had exactly the same experience a few years ago on my LX2: massive copper makes you feel like it’s OK as it doesn’t heat quickly. But after some time it gets burning hot and takes ages to cool down. It’s only inertia, it’s not really cooling. Copper with thin and tight fins only works with a fan on top of it. Without a fan, you need aluminum with sufficiently spaced fins so that free air can flow between them. Usually a good example is how fins are spaced at the rear of audio amps. Usually they’re thick, long, and about 1cm apart. That gives a good idea of what can work without a fan.
I think that heat sinks like this one (designed for 2U servers) could work much better:
https://www.aliexpress.com/item/1005003615973924.html
Otherwise I’ve had success in other machines with fanned heat sinks where the fan is placed in sandwich between two halves of heat sink, and runs at very low speed, making them totally silent, like this:
https://www.aliexpress.com/item/1005007349640045.html
They’re interesting because even a very minimal air flow is sufficient to keep a low temperature, and the rotational noise of the fan is dampened by the fins. However this one requires a real socket to attach to, one needs to find one that attaches to the back plate only.