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Written by Olin Coles   
Monday, 21 April 2008
Table of Contents: Page Index
Best Thermal Paste Application Methods
Mounting Pressure and Finish
Thermally Conductive Element Reference
Application on Round-base Coolers
Application on Square-base Coolers
Application on HDT Coolers

Mounting Pressure

Probably one of the most overlooked and disregarded factors involved with properly mounting the cooler onto any processor is the amount of contact pressure applied between the mating surfaces. Compression will often times reduce the amount of thermal compound needed between the cooler and processor, and allow a much larger metal to metal contact area which is more efficient than having fluid weaken the thermal conductance. The greater the contact pressure between elements, the better it will conduct thermal (heat) energy.

Unfortunately, it is often times not possible to get optimal pressure onto the CPU simply because of poor mounting designs used by the cooler manufacturers. Most enthusiasts shriek at the thought of using the push-pin style clips found on Intel's stock LGA775 thermal cooling solution. Although this mounting system is acceptable, there is still plenty of room for improvement.

Generally speaking, you do not want an excessive amount of pressure onto the processor as damage may result. In some cases, such as Heat-pipe Direct Touch technology, the exposed copper rod has been pressed into the metal mounting base and then leveled flat by a grinder. Because of the copper rod walls are made considerably thinner by this process, using a bolt-through mounting system could actually cause heat-pipe rod warping. Improper installation not withstanding, it is more ideal to have a very strong mounting system such as those which use a back plate behind the motherboard and a spring-loaded fastening system for tightening. The Noctua NH-U12P is an excellent example of such a design.

In all of the tests which follow, it is important to note that our experiments focus on the spread pattern of thermal paste under acceptable pressure thresholds using either a push-pin style mounting system or spring-loaded clip system. In most situations your results will be different than our own, since higher compression would result in a larger spread pattern and less thermal paste used. The lesson learned here is that high compression between the two contact surfaces is better, so long as the elements can handle the added pressure without damaging the components.

Heatpipe Directional Orientation

Heat-pipe technology uses several methods to wick the cooling liquid away from the cold condensing end and return back towards the heated evaporative end. Sintered heatpipe rods help overcome Earth's gravitational pull and can return most fluid to its source, but the directional orientation of heatpipe rods can make a significant difference to overall cooling performance.

For the best results, CPU-coolers should be orientated so that heatpipes span from front-to-rear with fans exhausting upward and not top-to-bottom with fans blowing towards the rear of the computer case. This removes much of the gravitational climb necessary for heatpipe fluid working to return to the heatsink base. In one specific example, the horizontally-mounted ProlimaTech Megahalems heatsink cooled to a temperature 3° better than when it was positioned vertically. While this difference may not be considered much to some people, hardcore enthusiasts will want to use every technique possible to reach the highest overclock possible.

Surface Finish Impact

If you're a painter, it's important to understand your canvas or else you won't know which paint to use. The same is true for enthusiasts wanting to overclock, or even just get the most out of their equipment. CPU coolers primarily depend on two heat transfer methods: conduction and radiation (heat-pipes also add convection). This being the case, we'll concentrate our attention towards the topic of conduction as it relates to the mating surfaces between a heat source (the processor) and cooler.

Because of their density, metals are the best conductors of thermal energy. As density decreases so does conduction, which relegates fluids to be naturally less conductive. So ideally the less fluid between metals, the better heat will transfer between them. Even less conductive than fluid is air, which then also means that you want even less of this between surfaces than fluid. Ultimately, the perfectly flat and well-polished surface is going to be preferred over the rougher and less even surface which required more TIM (fluid) to fill the gaps.

Ultra-120_eXtreme_Base_Closeup.jpg

This is important to keep in mind, as the mounting surface of your average processor is relatively flat and smooth but not perfect. Even more important is the surface of your particular CPU cooler, which might range from a polished mirror finish (such as the Noctua NH-U12P), to the absurdly rough (evidenced by the Thermalright Ultra-120 eXtreme pictured above), or the more complex (such as the OCZ Vendetta 2). Surfaces with a mirror finish can always be shined up a little brighter, and rough surfaces can be wet-sanded (lapped) down smooth and later polished, but Heat-pipe Direct Touch coolers require some extra attention.

Red_Scorpion_S1283_Surface.jpg

To sum up this topic of surface finish and its impact on cooling, science teaches us that a smooth flat mating surface is the most ideal for CPU coolers. It is critically important to remove the presence of air from between the surfaces, and that using only enough Thermal Interface Material to fill-in the rough surface pits is going to provide the best results. In a perfect environment, your processor would mate together with the cooler and compress metal on metal with no thermal paste at all; but we don't live in perfect world and current manufacturing technology cannot provide for this ideal environment.

So it's up to you to fix these imperfections through sanding or polish, and apply the magic amount of TIM to your project. But how much is enough, and what shape or pattern should be used? Read on to find out.

Benchmark Reviews invites you to share your comments and suggestions for this topic in our Discussion Forum.



 

Comments 

 
# ChampMark 2010-08-12 22:20
Thanks for this mate. It's made installing HDT coolers much easier for me.
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# RE: Best Thermal Paste Application MethodsJay 2010-09-30 06:09
Thanks Benchmarkreviews for this is a very informative article.
This kind of quality reviews makes it a lot easier for enthusiasts, like me, which do not have much resources for us to try such tests.
Thanks again... and i hope for more quality reviews from you guys..
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# Thanks for your work!Wilson 2010-10-31 12:09
Thank you for researching and publishing your work on applying thermal paste. I don't have a HDT heat sink, but the design is exactly the same as the Cooler Master Hyper 212 Plus Direct (blah blah the name is sooooo long).

Thanks Again!
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# Excellent Article!Twisted 2010-11-02 20:15
Thank you for a well written and presented article. I recently purchased a Xigmatek 'Red Scorpion' cooler to replace my stock Intel LGA775 cooler. Now I know how to best apply the paste! Also, my Red Scorpion was supplied with the white thermal paste, thanks again for explaining what these compounds are made from. I will throw out the white paste and get some that has a high silver content.
Cheers!
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# ExcellentMohammad 2010-12-01 20:15
Very well done. Just today I took apart a 212+ and noticed the truly pathetic contact I'd achieved using the Arctic Silver-recommended 'single line' method.

Definitely going this route next time.
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# Heatpipe Directional OrientationJim 2010-12-28 20:13
Olin, under the section "Heatpipe Directional Orientation" are you stating that it is better for the CPU cooling fan to point toward the top of the case, rather than front to back? I would think this would be true for PC cases that have the PSU mounted on the bottom of the case, and have a fan at the top, blowing outward. The new Lian Li PC-A04 case is a perfect example of this. Can you comment? (Thanks!) Perhaps a picture would be helpful here.
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# CorrectionJim 2010-12-28 20:28
In further reading, I realize that I didn't catch what you were explaning. I do understand what you are saying now. But my additional point/question is still relevant. If you take a look at the Lian Li PC-A04 case, wouldn't it make sense to re-orient the CPU cooler towards the top of the case? (They actually do not include a rear fan.) I would think that a vertical orientation of the heat pipes, along with a bottom to top fan direction would be optimal, considering that hot air rises.
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# CorrectionJim 2010-12-30 10:45
Correction: I would think that a horizontal orientation of the heat pipes, along with a bottom to top fan direction would be optimal, considering that hot air rises.
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# RE: CorrectionOlin Coles 2011-01-01 10:05
As you've stated, heat rises. Additionally, despite capillary action gravity still affects the heat-pipe fluid. It's best to orientate the heatsink so that heat-pipes are either level or collecting fluid at the base.
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# EarthwormJimEarthworm Jim 2011-03-29 15:15
Assuming that "BB" size is equal to 4,57 mm and "BBB" to 4,83, and as "LGA775" is 37,5 x 37,5 millimetres, and on the picture with the peas the pea is approximately 1/3rd of the diameter which results in 12,5 mm. which is 1,25 cm I do arrive to the conclusion that in you country agronomy is really advanced. In my country peas are generally around half a centimetre, which make them BBB size and almost BB size. So, in conclusion, the community
is still as keen as it thought, or in other words, it is not mistaken - your peas are mistaken ( they are really f***** up ;) ). I do hope this is cleared out, and I do hope that somebody confirms the size of the peas on the picture, based on my assumptions!
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# RE: EarthwormJimOlin Coles 2011-03-29 15:31
These were frozen peas, and they are slightly larger than a pencil eraser. In the photo, that bit of thermal paste was roughly half the mass of a BB, and it covered the entire contact base on an old LGA775 cooler.
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# Peas and such...StressLess 2011-08-13 16:52
The peas being referred to by the term "the size of a pea" (and in the fable "The Princess and the Pea") are the peas you make pea soup out of, which are dried peas. Dried peas are much smaller than frozen peas, about the size of the TIM you used in the now infamous frozen peas picture. But instead of peas, I had heard the amount to place was the size of a rice grain which also works and is less confusing.

On a different subject, I would liked to have seen the results of mounting the square cooler that you did a thin, even spread of TIM on. How did it look when removed?

Also I would like to see heat readings from all these different application methods. While you may want one or the other spreads visually, how does that translate into actual practice? Could less coverage translate into a thinner layer that increases metal to metal contact, yielding better results than 100% CPU coverage but thicker layer? Inquiring minds want to know!!
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# RE: Best Thermal Paste Application MethodsEarthworm Jim 2011-03-29 15:16
Still, thanks for the knowledge!
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# Hyper 212#3 2011-04-13 17:38
When using the line method with the thermal 212+ would I need two lines or three (since it has 4 copper pipes?
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# RE: Hyper 212Olin Coles 2011-04-13 17:43
Three. The number shall be three.
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# Meaning of the following statementMohan 2011-07-28 00:22
"it is important to fill the channels level with thermal compound so that the the additional material may spread somewhat unrestricted to the edges"

now what is 'channels level' we are talking about here?
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# RE: Best Thermal Paste Application MethodsMoto Psycho 2011-07-28 07:09
^Where you have pipes on the heatsink base, there are tiny dips as the surfaces meet, the base is not 100% flat, therefore it is vital that you ensure these channels are filled with paste to properly conduct the heat away from the processor
Moto
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# hands claplacky 2011-08-14 20:39
thanks for that. great job.
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# Deep HDT pipes?Traveller 2011-09-04 11:15
Hi Olin. I found your article to be extremely informative, thanks. I was wondering if you could shed some further light on whether or not failure to sand down an HDT cooler would make any significant difference for a pc that is never going to be overclocked at all. I would particularly appreciate your views on the Coolermaster Hyper TX3 cooler, which looks as if the the pipes are set too deep into the mounting base. See links below.

##overclockersclub.com/vimages/coolermaster_hyper_t x3/8.jpg
##goldfries.com/images/hwreviews/2010/coolermasterhypertx3/cmhypertx3_04.jpg

After having read your article, I have concluded that the two drops on the two centre partitions of the mounting base would be the best option for the Hyper TX3 cooler (to be used with an AMD Phenom II x6 1100T CPU), however, if sanding is not carried out, how would one deal with the space between the deeply set pipes and the CPU surface? Also, I have read that even merely touching the metal with a finger can cause grease and all kinds of particles to become stuck to it, so if sanding were to be carried out, how could one possible ensure that the cooler is thoroughly cleaned of all the residue from sanding? Thank you for any advice.
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# RE: Deep HDT pipes?Olin Coles 2011-09-04 12:00
Why would you ever sand/lap the surface of a CPU/heatsink that isn't going to be heavily overclocked? Almost any aftermarket cooler can handle stock voltage loads.
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# RE: Deep HDT pipes?Traveller 2011-09-05 06:54
Ok Olin, thank you for clearing that up. I'm new to all of this and didn't know if the sanding was recommended for 'normal' use or not.
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# RE: RE: Deep HDT pipes?Olin Coles 2011-09-05 10:31
Just use a thin amount of thermal paste over the CPU, and make sure to mount the heatsink as firmly as possible. This alone will give you more cooling performance than required.
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# RE: Deep HDT pipes?Traveller 2011-09-05 11:24
Is that in addition to the two drops on the two centre partitions of the cooler or only on the CPU? In either case, shouldn't I still be filling the channels on the cooler base? Thanks.
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# RE: RE: Deep HDT pipes?Olin Coles 2011-09-05 11:44
You can apply two drops, or you can use a clean finger to spread a very light film over the top of the CPU. I prefer to apply a thin film.
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# RE: Deep HDT pipes?Traveller 2011-09-06 06:47
Ok thanks for the advice, Olin.
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