Heatsink grease / thermal compound question

[Gene Pink]

Working on an HP laptop computer, it has some unknown very high viscosity grey thermal grease on the CPU and the Video processor chip/heatsink spreader interfaces. Likely not the original stuff, as some missing screws inside tell me I'm not the first to dig inside this beast, and the heatsink assembly needs to come off to get to where the missing screws are/were.

[rant] Touchpad assemblies should come out from the top, and not take five hundred and two various head type and length screws plus removal of the display and three thousand ribbon cables, just to get at the damn thing. [/rant]

Usually, I would just go with the old school white silicone/zinc oxide Dow 340 for this, but I noticed that while the grey grease on the CPU was still a bit pliable, it was rock solid on the video chip, it took toluene to cut it. It had hardened and dried solid presumably from overheating, so I want to get this right. I do a lot of gaming, Solitaire, and occasionally, Minesweeper. ;-)

Searching this board and the internet, there seems to be no consensus of whether the grey silver-laden stuff is capable of any more than a marginal increase in heat transfer.

Opinions on this would be greatly appreciated, is the grey stuff really worth a trip to the store? Never had it, never used it, but then again. I'm a transistor power amp repair sort of guy.

I read names mentioned such as Arctic Freeze 3 or 5 (sounds like a brand of freon for your car's AC).

Note that the grey compound I removed was a much thicker layer than it should have been for good heat transfer, maybe 0.015", and clamped by preset mounting springs that didn't have the oomph to squish it thin. Something lower viscosity, like the traditional white stuff would have oozed out more, and ended up much thinner.

Opinions would be greatly appreciated on this.

Thanks,
Gene

 

[JohnRoberts]

Back last year when I was messing with Peltier devices, using a chip cooler fan on the cold side of the peltier device, I bought a tiny tube of HS grease.

I don't expect much difference between different flavors of grease, but a huge difference between grease and no grease.

JR

 

[Gene Pink]

I don't expect much difference between different flavors of grease,

Thanks, JR, I'll just use the white stuff, and be done with it.

Gene

 

[CJ]

that grease is  mainly used to fill in imperfections in the metal surfaces so that there is more contact area,

most folks like myself do not know this, we think it is to transfer heat, so we glop it on there, then it compresses over time, contact pressure is reduced, and the transistors pop like jiffypop,

here is a highly detailed pic that took a few hours to make, finely illustrating this idea>

 

[JohnRoberts]

Yes, air is a poor thermal conductor.

JR

 

[Gus]

I think the differences are more with the carrier part of the compound. 
found some links
http://www.hardocp.com/article/2001/11/05/heatsink_compound_roundup
http://www.dansdata.com/goop.htm
http://www.extremeoverclocking.com/reviews/cooling/Thermal_Compound_Comparison_2.html

 

[Gene Pink]

I think the differences are more with the carrier part of the compound. 
found some links

And good links they are, all the more reason to not worry too much about the actual product. Thanks, Gus. The Australian guy testing toothpaste and Vegemite was funny, I want to drink a few Foster's with that dude, and then we can go throw boomerangs at kangaroos.

Apparently, the "what product to use" is less important than the application method.

Tonight I gave the ol' 5 oz. Dow 340 tube a good stirring on the drill press, as it is "just" a bit past it's expiration date. I don't figure the stuff goes bad, it just separates with the clear binder coming to the top, and remixing fixes that. I'll let is set for a day, probably has air bubbles in it after the mixing, and foamy, bubbly heat sink compound would be a bad thing, air voids.

CJ, That song envelope looks familiar. Clever way to make a point.

Any thermal compound has much worse heat transfer than the aluminum or copper heat sink. These copper ones as manufactured, are not as flat as they can be,  20 minutes of lapping on 600 grit on a master flat will fix that.

Then a "test" try, best guess as to how much grease to use, bolt it up, wait a day to spread, remove and see how I did. readjust and done.

Thanks for everybody's help, as it will be that much sooner until I start posting annoying jpegs again.


Gene