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Written by Olin Coles   
Friday, 09 October 2009
Table of Contents: Page Index
Best CPU Cooler Performance LGA1366 Q3-2009
Thermally Conductive Element Reference
Cogage TRUE Spirit
CoolAge CA-X120TF Wind Tunnel
Corsair H50 CWCH50
Scythe Kabuto SCKBT-1000
Scythe Mugen 2 SCMG-2000
Tuniq Tower-120 Extreme
ZEROtherm Nirvana NV120 PWM Premium
Cooler Surface Preparations
Cooler Test Methodology
Test Results: Stock Cooling Fan
Test Results: High-Output Fan
Enthusiast Fan Comparison
CPU Cooler Final Thoughts
Best CPU Cooler Conclusion

Surface Preparation

Processor and CPU cooler surfaces are not perfectly smooth and flat surfaces, and although some surfaces appear polished to the naked eye, under a microscope the imperfections become clearly visible. As a result, when two objects are pressed together, contact is only made between a finite number of points separated by relatively large gaps. Since the actual contact area is reduced by these gaps, they create additional resistance for the transfer of thermal energy (heat). The gasses/fluids filling these gaps may largely influence the total heat flow across the surface, and then have an adverse affect on cooling performance as a result.

Surface Finish Impact

CPU coolers primarily depend on two heat transfer methods: conduction and 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.

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 to the absurdly rough or the more complex (such as Heat-Pipe Direct Touch). 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.

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.

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.

Thermal Paste Application

The entire reason for using Thermal Interface Material is to compensate for flaws in the surface and a lack of high-pressure contact between heat source and cooler, so the sections above are more critical to good performance than the application of TIM itself. This section offers a condensed version of our Best Thermal Paste Application Methods article.

After publishing our Thermal Interface Material articles, many enthusiasts argued that by spreading out the TIM with a latex glove (or finger cover) was not the best way to distribute the interface material. Most answers from both the professional reviewer industry as well as enthusiast community claim that you should use a single drop "about the size of a pea". Well, we tried that advice, and it turns out that maybe the community isn't as keen as they thought. The example image below is of a few frozen peas beside a small BB size drop of OCZ Freeze TIM. The image beside it is of the same cooler two hours later after we completed testing. If there was ever any real advice that applies to every situation, it would be that thermal paste isn't meant to separate the two surfaces but rather fill the microscopic pits where metal to metal contact isn't possible.

TIM_Before_Spread.jpgTIM_After_Spread.jpg

After discussing this topic with real industry experts who are much more informed of the process, they offered some specific advice that didn't appear to be a "one size fits all" answer:

  1. CPU Cooling products which operate below the ambient room temperature (some Peltier and Thermo-electric coolers for example) should not use silicon-based materials because condensation may occur and accelerate compound separation.
  2. All "white" style TIM's exhibit compound breakdown over time due to their thin viscosity and ceramic base (usually beryllium oxide, aluminum nitride and oxide, zinc oxide, and silicon dioxide). These interface materials should not be used from older "stale" stock without first mixing the material very well.
  3. Thicker carbon and metal-based (usually aluminum-oxide) TIM's may benefit from several thermal cycles to establish a "cure" period which allows expanding and contracting surfaces to smooth out any inconsistencies and further level the material.

The more we researched this subject, the more we discovered that because there are so many different cooling solutions on the market it becomes impossible to give generalized advice to specific situations. Despite this, there is one single principle that holds true in every condition: Under perfect conditions the contact surfaces between the processor and cooler would be perfectly flat and not contain any microscopic pits, which would allow direct contact of metal on metal without any need for Thermal Interface Material. But since we don't have perfectly flat surfaces, Thermal Material must fill the tiny imperfections. Still, there's one rule to recognize: less is more.



 

Comments 

 
# March 11th cooler article?Hugo Martinez 2010-03-11 22:26
Where I am, it's March 12th. I've been looking forward to your March 11th "Q1-2010 Best CPU Cooler Performance LGA1366" article that was scheduled for March 11th. Is it already up but I'm too blind to find it? Or are you running late?

I need to buy a cooler but I promised myself to wait until I read the report.

Thanks!
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# Worth the waitOlin Coles 2010-03-12 07:39
Hello Mr. Martinez:

This article has grown much larger than first planned, and is expected to be published later this afternoon (3/12). It's worth the wait! :)
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# Hope it is worth the waitRaul Tano 2010-03-12 15:40
I'm in the same boat as Mr. Martinez. I eagerly await the article.
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# DiamondsJava_Az 2010-05-24 10:43
although Diamond is a polymorph of the element carbon.Diamond conducts heat better than anything - five times better than the second best element, Silver! I wonder what a diamond heatsink would set you back
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# MikeMichael 2010-09-26 09:34
Diamond only conducts heat in such a manner when it's aligned properly - therefore, you must grow a diamond, or fashion a diamond into a heatsink - you cannot combine diamonds as they would not match in alignment on the molecular level. This means you would need to start with a massive diamond.
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# wrong specificationjason 2010-08-10 13:19
Editors, can you correct the weight in the above specifications?
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# RE: wrong specificationOlin Coles 2010-08-10 13:20
Be more specific, and list your source.
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# RE: wrong specificationsjason 2010-08-12 01:41
#benchmarkreviews.com/index.php?option=com_content&task=view&id=371&Itemid=62&limit=1&limitstart=6

SCMG-2000 Specifications
Weight: 870 g
30.7 lb

It should be 30.7oz.
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# RE: wrong specificationsjason 2010-08-11 11:08
Sorry I was talking about the specifications of SCMG-2000.

#benchmarkreviews.com/index.php?option=com_content&task=view&id=371&Itemid=62&limit=1&limitstart=6
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# Can Mugen 2 fit in ThermaltakeV3 BE or Cooler Master 430 elite?Deen 2011-02-26 12:52
Can Mugen 2 fit in ThermaltakeV3 BE or Cooler Master 430 elite?
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