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THERMAL INTERFACE MATERIAL

Arctic MX-4 thermal interface materialThe CPU and GPU both are high power components in the typical gaming PC. CPU coolers generally use a fan and heatsink assembly that is clipped or screwed into place.

Gaming graphics cards use double slot coolers to support a thicker heatsink and cooler. Video cards can exceed 450W of power so excess heat has to be removed efficiently.

AMD provide their CPU with a heatsink in a box. The Phenom II comes with a heatsink featuring 4 heat pipes to remove more energy from the copper base.

The fan pushes air into the heatsink. Then it exits out the sides which then cools RAM and the regulators. Intel recently has shipped processors without a cooler, forcing users to purchase an aftermarket solution.

Even a bare fan assembly will cool the CPU and prevent it from self destruction. It will not run for long however unless its clocked down. The problem is that gaps between the CPU surface and the copper plate reduce the efficiency.

Over the years products called thermal grease or material have evolved as computers have become more powerful.

THERMAL CONDUCTIVITY

The idea for the thermal interface material is to be extremely thin. The thermal conductivity of the best thermal grease is well below copper or aluminum.

 

MATERIAL W / m °K
Diamond (impure) 1000
Silver 406
Copper 385
Aluminum 204
Coollaboratory Liquid PRO 82
Stainless Steel 16
Arctic Silver III 9.0
Arctic MX-4 8.5
Arctic Silver II 8.0
Cooler Master Premium 6.8
Cooler Master High Performance 4.18
Arctic Alimina 4.15
Zalman ZM-STG2 4.1
Dow Corning  TC-5026 2.89

 

Obviously the higher the thermal conductivity the better. Excess grease separating the metal surfaces more than the minimum necessary to exclude air gaps will only degrade conductivity, increasing the risk of overheating. Almost all machines we have serviced have used excessive material. Stainless steel is actually a poor thermal conductor and its shown to provide some comparison.

THERMAL PUMPING

The typical CPU cooler can move in the x and y axis. With about 15lbs of pressure the z axis is the most studied. Thermal expansion will increase the pressure as the device heats up. Vibration from fans will move the cooler slightly. The thermal interface material will then slowly migrate into voids where its needed.

The pumping effect works on a very small scale, typically below 1 micron. Due to the small scale, its now obvious excess material is inefficient.

Gap amd the thermal imterface materialLIQUID METAL

The liquid metal Coollaboratory Liquid PRO is not very user friendly. This is due to the CPU and cooler becoming bonded and inseparable. For this reason anyone wanting to use this type of solution should realize that any future CPU/cooler upgrade will not be possible. Arctic MX-4 is easy to remove for upgrades which is more practical. Coollaboratory Liquid PRO will corrode aluminum so copper coolers are needed.

ACER T320

Our old Acer T320 (new in 2004) has a 95W Celeron 335 CPU. The old CPU cooler fan had failed. We have an Intel branded fan handy it was put to service. We have some silicone thermal material but its thermal conductivity was insufficient to get the machine to throttle back the CPU fan. The machine ran fine but the CPU was warm under load, the CPU never tripped the thermal throttle. Once MX-4 was used, the CPU fan was able to throttle down at idle properly which reduced operating noise.

GTX 260

Our EVGA GTX 260 (new in 2008) has been a minor nuisance. The card was running far too hot and upon inspection we noted that the thermal grease was compromised.  Searching with Google, we found many threads over regreasing cards damaged by the 196.75 driver. See our page on video card overheating.

REGREASING

Using some cotton balls and some isopropyl alcohol is best for cleaning the heatsink and semiconductor surfaces. Its not a bad idea to use a small brush to clear away bulk material if necessary.

An old credit card or similar sized piece of plastic is ideal for spreading a thin layer of thermal material. Once the cooler is installed the material will soften and move to fill voids quickly.

Even when using a card to spread the material, its usually still too much. The layer should as thin as possible, its only to fill microscopic voids.

ARCTIC MX-4

We bought a small tube of Arctic MX-4 and we then regreased the Celeron 335 cooler and we noticed the CPU fan began to throttle back quickly after booting. Clearly the MX-4 demonstrated a better thermal conductivity as the CPU temperature was reduced considerably as well.

Next we disassembled the EVGA GTX 260 SC and regreased the card with MX-4 and after a few power down cycles the card seems to be much more thermally stable. Clearly Arctic MX-4 has better thermal conductivity compared to silicone and thermal pads. For overclockers, high quality materials are important.

COOLER OPERATION

With our machines repaired using the MX-4, we note that operating temperatures are lower. This means that less stress on the TIM itself will add to the service life generally.

TEMPERATURE

Based on the Arrhenius equation, which says that time to failure is a function of e-Ea/kT where Ea = activation energy of the failure mechanism being accelerated, k = Boltzmann’s constant, and T = absolute temperature. The life of an electronic device is directly related to its operating temperature. Each 10°C (18°F) temperature rise reduces component life by 50%. Conversely, each 10°C (18°F) temperature reduction increases component life by 100%. Therefore, it is recommended that computer components be kept as cool as possible (within an acceptable noise level) for maximum reliability, longevity, and return on investment. Given the 10°C reduction, the 300R chassis pays for itself with reduced PSU costs due to thermal failures.

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