Thinkpads Forum

A forum member has been reading a few of my posts and wanted to pick my brain in a PM about what I know about thermal grease... Posting out here so as to let more people benifit from some info and probably flame/argue my points Some of the info is to directly answer the members PM, the other I offer only to help others

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Thermal (Grease - Compound - Adhesive)
Grease & compound are used interchangably... they are one in the same afaik. Adhesive on the other hand is for attaching heatsinks, like to ram chips on a video card (I would never use on a CPU )

Brands/Types
The only one i have used (since 2001) is Arctic Silver 5 in a 3.5gram tube. It has always done what I needed, so I have never felt the urge to try any of the others (they are starting to get really exotic with this stuff). Maybe in an extreme overclocking situation where every degree matters, then the "better" stuff might be in order. IMO AC5 (Arctic Silver 5) is the "better" stuff.

It only takes a very small ball added to the chip... a sinlge tube will last me for at LEAST 10 to 12 machines (more on that later).

http://www.newegg.com/Product/Product.a ... 6835100007

Cleaning, surface prep
As far as cleaning, I use an expired credit card to scrape away old stuff, then just plain old alcohol from the pharmacy section of Wal-Mart. For "rags" I use a package of DRIED OUT baby wipes .

Just remove the big stuff with a plastic scraper, clean with alcohol, then apply a very small ball of grease/compound to the cpu, and pop the heatsink on.

IF the heatsink has a FLAT surface, not recessed or anything (saw one wierd recessed one recently in this forum), I get away with even a SMALLER ball of compound... and you can also "lap" the surface of the heatsink...

Buy some wet/dry black sandpaper (auto parts, wal-mart), in 400, 600, 800, 1000, 1500, and 2000 grits... a flat surface(i use a piece of glass from an old scanner), and some water.

WET the 400 grit, sand for like 10-15 seconds with very light pressure (glass on bench, sandpaper black side up on glass, heatsink in upright position, circular motions. (400 grit dont take long at all)...

then repeat with 600, 800, 1000 & 1500 (water is your friend with this type of sandpaper, the cleaner it stays, the better of a job it does)

When you get to 2000 (this stuff feels like paper, the grit is so small you honestly can't feel it), spend a fair amount of time sanding, the heatsink will be at an almost mirror finish... What this does is remove all the imperfections in the heatsink, thereby almost eleminating the need for thermal compound. It ain't NASA perfect, so you still use AC5, but in VERY small quantities.

I'll repeat, THE main things are to keep your sandpaper clean(lots of water), I personally use circular motions, and dont overdo the bigger grits(lower numbers).

Cure time
You'll hear about a "cure" time on this stuff too, what happens is as you use the machine, the compound heats up and flows somewhat, distributing it better... but in my experience, the curing time has never made more the a few degrees in temperature difference. like 5C MAX... so if you fire up a machine and the temps are WAY off... recheck your work (this also gives you a chance to see really how little compound was needed... ALL that is squished out around the cpu was WASTE.

Amount to use
Now, all this info on amount is intended for the newer CPU's that you can SEE the CPU die itself (the little bluish purplish chip in the center of the CPU)... that is the only part that needs the compound.

i.e.
http://cdn.cpu-world.com/CPUs/K7/L_AMD- ... 8ES%29.jpg

Older CPU's that the die was hidden by either ceramic or metal, they require a bigger ball (and benifit more from lapping)

i.e.
http://www.techwarelabs.com/wp-content/ ... pu-die.jpg

http://andreaz.an.funpic.de/images/P166mmx.jpg

The whole purpose of the thermal grease is to fill any tiny imperfections in the surface of the heatsink so that you get MAXIMUM contact with the CPU. Too much doesn't hurt, but is a TOTAL waste.

Conclusion (other thoughts)
Heatsink "grease" is compound, ONLY for heat transfer between 2 surfaces, it is not a lubrication.

AC5 is ALWAYS better then stock/factory compound.

1 tube will last modern CPU's for at least 10 machines.

It stores REALLY well, I have used a 5 year old tube before that the compound was still the same viscosity as it was new. (While I DO always replace factory crap with it, once I do, I have never had a need to redo it, even years later on removing the heatsink, the AC5 was still fluid like).

Awesome! Thanks a lot for the info. Time to change out some old noisy fans

Daniel.

Thanks, great stuff!

Is lapping something you'd recommend that I do with the heatsink in my T400? I have been considering redoing the paste with some AS5.




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Lapping is not nessacery at all, but it can gain you a few degrees lower cpu temp... On machines I plan to keep for a long time (mainly my desktop), I lap new heatsinks. My desktop normally runs idle at about 5C above ambient, heat is the normal eventual reason for most electronic failures... I figure the cooler the better

I think I'll just let that be for now, I'm sure it would work just fine but I don't want to risk sanding it too much and ruining it or breaking the connection with the GPU. It seems like it would make more sense on desktops where they are not all in one units. On a warm day idling the CPU runs at 30 Celsius, so not bad at all. Next time I do a routine clean I think I may as well redo the paste anyways.

Thanks again, good to have all that info in one place. Maybe this would qualify as a how-to, and be moved to the respective forum?


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Would definately apply on desktops moreso, on a laptop I would start with like the 1000 grit... REALLY hard to remove material with that... Dunno if you've ever had a manicure... but it is the same process... they usually use a 4 sided "file", rough, fine, extra fine, then a leather buffing pad.

Just skip the rough, go straight to the fine, the only thing it will remove easily is the ridges.

I found it best to practice on something easily used as a guide... like a penny... you can easily see how much you are removing, and it gives you a good idea of how much pressure to apply for how long... lapping a penny would definately require the lower(bigger) grits to start out with.