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Pretty or functional heatsinks?

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Slake

Senior Member
Joined
Jan 12, 2001
Location
Knoxville,Tn
I was just wondering what you all thought about the article http://www.overclockers.com/tips458 from the front page which states that a perfectly smooth heatsink will not perform as well as one with "micro valleys". Polishing mine to a mirror finish may have been a mistake. Since I lapped and polished prior to installation I don't have before and after specs to compare. The theory of the article makes sense to me. Maybe we can get some before and after temp comparisons from some of you peeps who have polished their heatsinks? How about it toothpaste troopers? LOL. ;D
 

DrMac

Registered
Joined
Dec 18, 2000
I also just read that article, and it seemed to me that the author neglected to attempt to try his microfinished HS's WITHOUT thermal compound when attaching them to his crystals. He seemed to be implying that the thermal compound interfered with heat transfer when the HS's were "too" smooth, because it couldn't be squeezed out of the way when there weren't enough peaks and valleys to hold the excess. This would imply that the TC would not be necessary if the mating surfaces were so smooth that the TC got in the way. We all know that TC is only needed to fill the voids of imperfect finishing, and that even the best TC is not as good as direct HS to substrate contact. Otherwise, we'd all be using gobs of TC between our HS's and CPU's. This is a situation where sometimes "less is more", and by extension, it would seem possible to reach a point where "none is the most". Of course, I'm not advocating that everyone throw their Arctic Silver in the nearest trash bin, but it would appear (based on this article) that we could reach a point of diminishing to negative returns by the use of any TC.
I realize that the author apparently had access to very sophisticated machinery to flatten and polish his HS's, which most of us would not, but it raises the possibility that if the HS and CPU are both highly polished and flat, that the TC might become an unnecessary component in the equation.
Perhaps an experiment could be done to see if once a certain smoothness/flatness spec is reached, that TC becomes a hindrance, rather than a help in facillatating heat transfer.
Just a little food for thought.
 

Slain

Member
Joined
May 15, 2001
Location
Woking (near London) U.K.
I would guess that point would be reached when the particle size of the thermal compound exceeded the height of the surface imperfections.
That raises the possibility that if you have extremely flat surfaces in contact you would eventually be better of with a silicon oxide based compound with it's fine structure than a coarser metallic compound.

*brain explodes*
 
W

William

Guest
ok, now we are putting our thinking caps on. My guess would be if you lapped your sink in your basement, and even if it is mirror like and all, you still have grooves big enough, because he is gonna have much better tools to level stuff out with. But yes, maybe silicon based stuff would work better. I do like Colin's idea he has posted, to use Artic Silver as the lube for the ultra fine sandpaper.
 

Slain

Member
Joined
May 15, 2001
Location
Woking (near London) U.K.
Having cogitated a bit more I don't think grooves are the problem. It is well known that people can make their own astronomical mirrors and these can be ground to a smoothness of 1/4 to 1/10 of a wavelenght of visable light (125-50nm) in a home enviroment.
The problems start trying to get the faces of the die and HSF pefectly *flat*
as opposed to *smooth* i.e. avoiding large scale height changes against micro imperfections. Getting the faces really flat would probably require laser interferometry possibly a bit beyond a home workshop :)
Oh and then the two flat faces would have to exactly parallel as well to ensure even pressure over the surfaces.
Hmm Arctic silver is sounding better and better
 
OP
Slake

Slake

Senior Member
Joined
Jan 12, 2001
Location
Knoxville,Tn
Great dicussion guys.I always hear of drops in temps after lapping. Either that means the article is interesting but wrong or the results reported by oc'ers are for heatsinks that were not lapped unto a mirror finish. I want to see some before and after comparisons but cant afford a new heatsink right now. I guess to properly test, you would need two heatsinks. Test both unlapped with AS. Lap one with 600grit and don't polish it, and lap / polish the other to a mirror finish and test with and without the AS. All that would be a lot of wear and tear on someones CPU and Socket. I've gotta admit the article had me convinced until I thought of all the reports of better temps with lapped heatsinks. Shadow just put a mirror finish on a HS. Maybe he'll share the results if he tested the HS before polishing..
 

dimmreaper

Senior Member
Joined
Dec 16, 2000
Location
home
I think that as long as you reduce the amount of thermal comound as the sink gets finer then no harm can be done by polishing. I don't even put a dab of goop on when I put it on. I take a piece of a plastic wal-mart bag, applie the TC to the bag the rub it on the sink and core, just enough to leave a greay haze on the parts.
 

The Stickie

Registered
Joined
Mar 2, 2001
Location
Belgium
there is one detaile most of you seem to forget: your cpu is NOT perfectly flat, this guy's cristal probably is...
so I you flatten your hsf, things can only get better...because the space between your chip and the hsf will become smaller (not dissapear)
 
OP
Slake

Slake

Senior Member
Joined
Jan 12, 2001
Location
Knoxville,Tn
OK, I shoulda listened to you guys. Last nite I got a wild hair and decided to test this theory. I relapped with 600 grit and re-installed the HSF with Arctic Silver 2. I know he said "not more than 800 grit for final lap", but that implies that 600 would be good. Before temp was 32C idle and 44C full load at 25C ambient with the FSB @108 and VCore @ 1.95. After: Idle 38C load; unknown, I shut down when temp reached 52C! This was with factory FSB and VCore. I re-installed twice thinking I may not have a good interface but got the same result both times.
Oh well, back to the old lapping board with my 2000 grit final lap followed by the famous Shadow Colgate treatment.