Cpu heatsink should it be shiny or black underneath

Hello folks. I have a Dell Inspiron 8600 notebook with a Pentium M chip. About a year ago I replaced the CPU with the fastest that I could fit.

The heatsink has a small contact square that sits against the die of the processor. I recoated this correctly with new heatsink paste. However, around the die contact on the heatsink, there was a sort of grey-black coating. This was very thin and not at all sticky or goopy. To be clear, it was on the whole underside of the heatsink apart from the die contact patch in the centre. It seemed like it was just a very thin layer of oxidisation or tarnish. I cleaned it off using a cleaning alcohol. This left the underside of the heatsink a silver foil, apart from the small contact square with the heatsink paste on it.

I reinstalled everything but since then I've been worried that the silver surface on the bottom of the heatsink may be reflecting radiated heat back at the CPU, whereas the black/grey coating may have been there to help absorb radiated heat into the heatsink. Or is this not a problem? The fan does seem to fire up at odd times, when the computer doesn't seem to be doing much, but I do also suspect my Windows installation of being flaky because it's been a few years and the system has had a lot of stuff installed, reinstalled, registry problems etc. (I guess it could be the video chip fan that i'm hearing too).

I'm wondering whether I should be looking to somehow blacking up the underside of the heatsink again, or not worrying about it. I have seen a lot of discussion about a black goop but this was not a goop, neither was it anodised, like I said it was more like a tarnish or graphite coating. Came off pretty easily.

I am fearful that this notebook may be reaching the end of its life, ie the motherboard is cracking up because sometimes the USB ports and wi-fi stop working and it crashes a lot lately. But it has a lovely really hi-res screen on it so I'm trying to extend its life - possibly even reuse the screen on another notebook if possible.

Would appreciate some advice on the heatsink issue - thanks!

Waz

The thin dark greay area sounds like it is old thermal compoubnd residue. Some TIM is very light coloured in appearance (AS 5 MX5 etc) but some other OEM stuff and even the stuff Intel uses is quite a bit darker.

Did you use a TIM removal solution ?

@ulysses35, the silver area I'm talking about was not actually touching the processor, so why would it be coated with thermal compound? there was only a small centre patch of the heatsink that in contact with the centre die of the CPU.

i thought the job of the thermal paste was just to conduct heat where there is direct contact. so why would it be applied to an area of the heatsink that doesn't actually touch the processor? is it to insulate the heatsink, ie to stop it radiating heat back at the processor?

many thanks for helping me to understand how this stuff works.

Scraping off the foil--or whatever it was--shouldn't cause any problems so long as you applied thermal paste and put the heatsink on properly. Black does absorb heat better, but it shouldn't make any difference in this kind of application.