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Reviews - Featured Reviews: Cooling
Written by Olin Coles   
Thursday, 01 January 2009
Table of Contents: Page Index
Best CPU Cooler Performance LGA775 - Q4 2008
Thermally Conductive Element Reference
CoolIT Domino ALC
GlacialTech UFO V51
Thermaltake SpinQ CL-P0466
Thermaltake V1 AX CL-P0508
Titan FENRIR TTC-NK85TZ
Zalman CNPS9900 LED
TIM Application and Surface
Testing Methodology
Test Results: Stock Cooling Fan
Test Results: High-Output Fan
CPU Cooler Final Thoughts
Best of Q4 2008 Conclusion

Thermal Interface Material Application

Over the past several months, I have read an unreasonable number of discussion forum posts which offer inaccurate and often times incorrect information. It's not really all that surprising to read poorly conceived information on the Internet, which seems to be a anonymous means of passing off opinion for fact. As a general rule we don't let too many things go untested, and the advice of wanna-be experts is not doing the hardware enthusiast and overclocker community any good. In this article, Benchmark Reviews dispels myth and establishes fact on the topic of proper application in our Best Thermal Paste Application Methods article.

After we wrote our 33-Way Thermal Interface Material Comparison article, 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.

Surface Finish Impact

Here's the part I've been waiting to reveal... the importance of surface finish in relation to the impact on thermal conductivity. CPU coolers primarily depend on two heat transfer methods: conduction and radiation (heat-pipes also add convection). This being the case, let's start with conduction as it related to the mating surface between a heat source and a cooler.

Because of their density, metals are the best conductors of thermal energy. As density decreases so does conduction (of heat), which relegates fluids to be naturally less conductive, and gases as virtually non-conductive. So ideally the less fluid between metals, the better heat will transfer between them. Ultimately though, this means that the perfectly flat and well-polished surface (Noctua NH-U12P) is going to be preferred over the rougher and less even surface which required more TIM to fill the gaps (Thermalright Ultra-120 eXtreme).

Heat radiation is different however, and requires exactly the opposite. Because gases (air) are naturally poor heat conductors, surface area of the heatsink is key to the cooling performance through convection. This type of cooling is what you commonly see in automobile radiators, which utilize large arrays of metal fins to radiate heat to be drawn away by a fan. The same is true for the CPU cooler, which needs as much surface area as possible to optimize it's radiative effects. OCZ and others have recognized that the surface of a heatsink does not have to be the sum of its overall size. By adding dimples and bends, the surface area is increased without growing the overall dimensions.

To sum it all up, science teaches us that a smooth flat mating surface is ideal for CPU coolers so that less Thermal Interface Material is used. Because these coolers are using fans to force air over the heatsinks fins, the overall surface area of those fins should be as large and uneven as possible. In the next section we'll find out just how well all of these principles worked for our collection of test products.



 

Comments 

 
# RE: Best CPU Cooler Performance LGA775 - Q4 2008SGT 2010-03-02 11:28
Used this for about 8 months and it started to leak around the pump area work well but in not up to the job in a long hall i replace it with a CORSAIR CWCH50 Hydro Water Cooler...and never look back
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# RE: Best CPU Cooler Performance LGA775 - Q4 2008Michael 2010-07-01 22:55
I used it for 6 month, not so good especially at low speed fan. Once you increase the fan speed it becomes very noisy!
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# Good CPU Cooler BUT MOBO CooksGraham 2010-11-10 06:13
As with most replacement ccolers you have a trade off.With Sttandard cooler you have reduced cooling available for overclocking yet you still have the mobo components cooled by the same fan.With this cooler solution you get amazing cooling if maybee a little noisy when ramped up,I use it on a intel Quad 6600 running at almost 4gig (per core) overclock on a top end Lanpsrty Mobo.The Cpu runs idle at 28-30deg and Sressed when benchmarking at 48-50 so really good.The biggest problem is, even when used in a huge custom case with 2 x 250 mm case fans and three 120 rear fans (One of which adds pull action to the Radiator of the coolit) i have a major problem with the motherboard cooling sometimes hitting in excess of 60 deg which causes all sorts of issues. So to conclued it is a great product If your not doing extreem Overclocking. BUT i Intend to replace it with a Noctua NH-C12P SE14, AM2/AM3/775/1156/1366 which has a 140mm downward facing fan to keep the mobo temps under control.
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