Very Tiny black dots on CPU Heatsink base

[nexusN]

Hi all,

I have a question on the CPU cooler's stain.
Currently I am using a Noctua NH-C14, installed since Sep, I clean it monthly.
Yesterday when I was taking it out for cleaning, after removing the thermal paste, I found that there are a few black dots attached on the surface of the heatsink base, like sand.

They attached firmly, on touching I can feel them there.
I tried to clean it with alcohol, then with a pinpoint to try to take care of it, no luck but leaving a small scratch on the base:'(

Do you have any idea why they are there?
Everytime before I install the heatsink back, I clean and make sure no residue are left on both surface(CPU and heatsink), so I have totally no idea how they are formed when cooling the CPU.

The thermal paste I am using was NH-10 following the cooler, soon I switched to Gelid GC-Extreme.

Is it some kind of manufacturing defects, any possible ways to deal with them?
Although the temp now looks good, on Xeon E3-1235, ambient Temp 24C, the CPU is as low as 31C, I still want to know if there are way to take care of the stains, at least to prevent them from accumulating.

Thank you for your attention.

 

[Throckmorton]

Why do you clean it monthly? All you're doing is putting stress on the CPU/motherboard. And thermal paste takes time to cure, which you're wiping out every time you clean it.

I don't know what the black dots are.

 

[nexusN]

Why do you clean it monthly? All you're doing is putting stress on the CPU/motherboard. And thermal paste takes time to cure, which you're wiping out every time you clean it.

I don't know what the black dots are.

The concerning computer is a server running 7x24,
It is cleaned so frequent as my home is extremely dusty, with lots of vehicles going to and fro near by my building.
The performance goes down to a significant extent after like a month, and I can see the accumulation of dust in every fins of the cooler.

I have already installed dust filter and ensure positive pressure of the chassis, it just doesn't seem working.

 

[deimos3428]

Are they diesel-powered vehicles by any chance?

I once worked in a telecom co-lo attached to a garage that housed a lot of heavy trucks. The ventilation system was...not well thought out. To make a long story short, we ended up sucking diesel fumes through some rather expensive gear over a period of several months, where the fine particulate settled as a black greasy film.

It's possible you trapped something like that in the paste at some point while reseating the heatsink, and it stained after being heated. But I'm just throwing that out there as wild guess because you mentioned the vehicles.

As for cleaning the HSF, why not just use compressed air? No need to remove/reseat it.

 

[nexusN]

Are they diesel-powered vehicles by any chance?

I once worked in a telecom co-lo attached to a garage that housed a lot of heavy trucks. The ventilation system was...not well thought out. To make a long story short, we ended up sucking diesel fumes through some rather expensive gear over a period of several months, where the fine particulate settled as a black greasy film.

It's possible you trapped something like that in the paste at some point while reseating the heatsink, and it stained after being heated. But I'm just throwing that out there as wild guess because you mentioned the vehicles.

As for cleaning the HSF, why not just use compressed air? No need to remove/reseat it.

Thank you for your ideas,
but I am actually living on 10th floor, and the vehicles are mainly buses which the pollutants are not the mentioned.

I am now communicating with Noctua supports,
and on testing, luckily there aren't much effect on cooling seems, so I may now leave it, and hope there won't be more in the future.
For compressed air, I use a small pump to clean the dust on the surface as the final step actually.

Now I suspect that they are some drop out from the CPU shell, photos were sent to Noctua and pending their judgement.