I have seen pictures of the Nuc8i5 disassembled. I also own one. Below the fan is the copper heat sink. This heat sink is fixed with 4 screws to the motherboard.
Is this a standardized screw-positioning? Am I able to buy a heat sink that fits this screw placement? How would I find a list of compatible heat sinks?
This is a custom heatsink designed specifically for this processor and this NUC design. There are no replacement or upgrade options available on the market. You should not touch it.
There are multiple third-party companies that offer fanless chassis that can be used with the NUCs. In these cases, the NUC's heatsink is replaced by the thermal mass that attaches it to the chassis. I do not know whether your particular NUC has an available fanless chassis because you have improperly described it (see Intel NUC Product Code Naming Convention for more information; you typically use what they've called the family code (which is really an acronym for the model's code name) and only add the processor designation if this is important to the conversation (for example, i5BE vs. i7BE)). I personally cannot recommend using any of the available fanless chassis as the NUC's are designed to have their blower generate continuous airflow over both surfaces of the board and fanless chassis do not (IMHO) generate enough (convection) airflow to properly cool other components on the board. This can negatively impact the lifetime of the NUC. Still, if this is your desire, go for it.
Thanks for the answer.
So the placement of the heatsink-screws is completely NUC specific and not a single heat sink out there would fit? Not even adjustable mounting brackets? Is there a technical drawing showing the exact distances between the screws, the screw type (metric size), etc?
I am aware of the risks of passive cooling. Still, in the NUC bios you can - without hacks - also slow down the fan quite a lot if you want to. Seems to be on-par with good passiv cooling - especially when the components are layed out in a new bigger enclosing where air can more easily move.
Well, you never know; you might get lucky and match one.
Mechanical drawings can be found here: https://www.intel.com/content/www/us/en/support/articles/000006820/mini-pcs.html. I have no idea whether they document this portion.
Yes, you can even turn the fan off. This configuration capability is provided specifically for fanless chassis. Using it improperly to try and make the system quieter is a fools errand, if you ask me. Making systems this small has its drawbacks. Live with it.
AIDA64 is a good tool to do this with. It detects and accurately identifies all of the sensors available (unlike most of the other third-party tools) and offers a built-in stress capability. There is a try-before-buy option so you can try it out without having to pay for it.
Hope this helps,