Cooling Not-so-common chips

[Foxie3a]

well, of course not something like that, I'm just saying the little unknown stuff..

 

[SunRedRX7]

thermal compound is not electronically conductive (mostly) and I am not putting it on the wires or anything!

http://www.arcticsilver.com/as5.htm
Not Electrically Conductive:
Arctic Silver 5 was formulated to conduct heat, not electricity.
(While much safer than electrically conductive silver and copper greases, Arctic Silver 5 should be kept away from electrical traces, pins, and leads. While it is not electrically conductive, the compound is very slightly capacitive and could potentially cause problems if it bridges two close-proximity electrical paths.)


AS3 was the same to, but since they longer sell it, they have very little info on AS3 on the Artic Silver Site.

 

[Foxie3a]

wouldn't having thermal compound on a chip let the heat come off of the chip faster, then the air can cool the compound?

 

[docwax]

wouldn't having thermal compound on a chip let the heat come off of the chip faster, then the air can cool the compound?

probably not. the thermal compound is designed to bridge the gap between the chip and the heatsink because the air in between traps heat. since it is not possible to have the heatsink and chip fit together perfectly, compound fills in the holes. but some conductivity is lost when the compound is used. without a heat sink, the compound is counter productive, but not enought to make a difference.

 

[Foxie3a]

oh well, if it doesn't cool enough to make a difference, then it won't heat it up enough to make a difference..

I think that I will be getting some thermal adhesive and stick heatsinks on everything then..lol

 

[redPEPPER]

wouldn't having thermal compound on a chip let the heat come off of the chip faster, then the air can cool the compound?

No. The compound is not some sort of magic heat absorber. A layer of compound on a chip will never be warmer than the chip itself, so for the same surface of contact with air, it won't cool as much. The chip might actually end up warmer than without the compound.

It probably needs to be reminded: thermal compound is a VERY POOR heat conductor, when compared to such thing as metal, water or even toothpaste. But thermal compound is a much better conductor than air, and is much more stable under heat than toothpaste. That's its use: replace the air between the chip and the heatsink. It's much better to have compound between the chip and the heatsink than to have air. BUT it's not better to have a thick compound layer because the thicker it is, the worse heat goes into the heatsink.

Compound alone on a chip works a little like a heat insulator. Quite the opposite of what you want to achieve.

 

[Foxie3a]

but why? it is 99% silver,and that is better than even copper.

 

[CrashOveride]

wouldn't having thermal compound on a chip let the heat come off of the chip faster, then the air can cool the compound?

No. As I said thermal compound isn't all that great of a thermal conductor. Its better for the air to just cool the actaul component rather than the past unless you add a substantial amount of suface area.

EDIT: BTW, AS Thermal Adhesive not 99% silver. The silver in it is 99% pure micronized silver, its only 62-65% silver (by weight).
AS5 is also less than 99%. They say:

From AS5 website
Arctic Silver 5 contains over 88% thermally Conductive filler by weight.

Don't know if that means there is 88% silver or 88% goop with <=22% silver. Not sure exactly what Conductive Filler reffers to.

 

[Foxie3a]

OK, I got it now..so sanding the heatsink would be very good, so then you could use much less thermal compound, right?

 

[CrashOveride]

OK, I got it now..so sanding the heatsink would be very good, so then you could use much less thermal compound, right?

Pretty much yes. Thats why people do it.
Some people have even lapped their processors! (scares me)

 

[Foxie3a]

and what is lapping again?

 

[CrashOveride]

and what is lapping again?

Sanding it (gradually going to a more and more fine grit - on the sand paper that is).

http://forum.oc-forums.com/vb/showthread.php?s=&threadid=70679
There is also a little OCing terminology thread somewhere, dont know where though :/

 

[Foxie3a]

so using 800, 900 then 1000 grit sandpaper in a row? for example.

 

[CrashOveride]

so using 800, 900 then 1000 grit sandpaper in a row? for example.

Well, more like 200, 400, 600 (800, 1000, though people often stop at 600).

But really the best part is getting the heatsink flat (as in not tilted), as opposed to getting it smooth. Smoother should yeild better results (since less of the comparably bad thermaly conductive paste is used) but some test have shown that lapping it too much can actualy hurt preformance, though not many results, I only saw it once. Besides for smoothness the less amount of space is negigable and under certain circumstances it might be more:

The light grey is the paste, in the first example, when pushed down the processor (bottom) and heatsink (top) would fit together very well - though this would be an amazing coincidence - and give better transfer then the well lapped example below.

 

[Foxie3a]

yeah, that's what I thought.

 

[hawtrawkr]

if your interested in lapping you can look into getting a lapping disc there alot better for lapping than sandpaper

 

[Foxie3a]

well, then what is a lapping disk?

 

[hawtrawkr]

a lapping disc is part of a kit you would use to lap a cpu or hs with
its usualy better to use than sandpaper because of the motion you use it with

kinda like when a carpenter needs to plane a door down and goes from one side to the other with the plane with paper people tend to want to make circular motions over the top but that can concave the surface your trying to flatten

 

[CrashOveride]

a lapping disc is part of a kit you would use to lap a cpu or hs with
its usualy better to use than sandpaper because of the motion you use it with

kinda like when a carpenter needs to plane a door down and goes from one side to the other with the plane with paper people tend to want to make circular motions over the top but that can concave the surface your trying to flatten

Well if you lap properly you put the paper on the table (flat and smooth table) and keeping the HS flat drag it down the sand paper. THere is a good guide in one of the stickies I think. Or at least there was.

 

[squeakygeek]

a lapping disc is part of a kit you would use to lap a cpu or hs with
its usualy better to use than sandpaper because of the motion you use it with

kinda like when a carpenter needs to plane a door down and goes from one side to the other with the plane with paper people tend to want to make circular motions over the top but that can concave the surface your trying to flatten

...And people can use circular motion with a lapping disc. People can also drag and lift using paper. The benefit of a lapping disc does NOT come from some kind of psychological problem.

And actually, the surface would become convex, not concave.