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Thermal Interface Material


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#1
Digerati

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An often misunderstood and sometimes overlooked critical hardware component is thermal interface material or TIM. TIM is typically seen as a thermal pad on a CPU heatsink, or in paste form. It may also be called thermal grease, silicon grease, heat transfer compound, thermal paste, heat sink compound, or goop. There are probably several more names.

The purpose of TIM is to ensure all the microscopic pits and valleys in the CPU die and heatsink mating surfaces are void of heat trapping air, maximizing surface to surface contact. Any excess is too much and gets in the way, and can actually be counterproductive to the heat transfer process.

The 4 Most Common Heatsink Fan (HSF) Assembly Mounting Mistakes:

  • Failure to use TIM
  • Used too much TIM
  • Reused old TIM
  • Did not clean mating surfaces thoroughly before applying TIM
Materials Needed: One clean plastic shaft Q-Tip (cotton swab), acetone or 91% isopropyl alcohol (Note - most rubbing alcohol is 70% and leaves a film. 91% alcohol can be found at your local drug store), clean scissors, can of compressed dusting gas, and the TIM. I recommend one of the new generations of non-metallic TIMs such as AC MX-2, Tuniq TX-2 or, OCZ Freeze or the venerable silver based TIM, Arctic Silver 5.

WARNING: Keep yourself grounded with the case to ensure there is no static buildup and discharge that might destroy any electrostatic discharge (ESD) sensitive devices. It is important to realize that the "threshold for human awareness" for a static shock is higher than the tolerance of ESD sensitive devices. In other words, you can shock and destroy a CPU, RAM module, or other sensitive device without even knowing there was a static discharge! Use an anti-static wrist-strap or frequently touch bare metal on the case to maintain your body at the same potential as chassis (case) ground.

Preparation: Power off and unplug the computer from the wall. Cut off one cotton swap near the end. Bend the plastic shaft about 1/2 inch from the cut end to make a nice little hockey stick. This is the working end of your TIM application device. Clean the die and heat sink mating surfaces with a soft, lint free cloth dampened (not dripping wet) with acetone or 91% alcohol. Do not let any fluids run down the sides of the CPU die. Clean skin oils from the working end of your applicator with the alcohol dampened cloth. Blast the surfaces with a quick blast of compressed air to ensure the surfaces are dry and no lint or dust remains behind. Do NOT touch the CPU die or heatsink mating surfaces, or the applicator's working end from this point on.

Application: Apply one "drop" of paste, about the size of a grain of rice, on the corner of the die and spread it out across the die with the applicator, like spreading icing on a cake. Spread the paste as thin as possible while ensuring complete coverage. It is easier to add more than remove excess. Remember, too much is counterproductive.

Note 1: Depending on the type of TIM used, some, such as the silver based compounds, can take 2 - 5 days or longer (depending on the power/heat up-cool down cycles) for the TIM to cure and reach optimum effectiveness. A 2 – 4°C drop in average temperatures may be realized after curing.

Note 2: A new HSF may come with a thermal interface pad already applied. Those pads consist of mostly paraffin, which is supposed to melt and squirm out of the way when the CPU heats up for the first time. Thermal pads are certainly better than no TIM at all, but they are not as effective as silver or ceramic based compounds. Do not use a sharp or metal object to remove the pad. A fingernail will work fine, removing any residue with acetone or alcohol.

Note 3: Do not reuse a thermal pad or paste. Always remove the old, cured TIM, clean the mating surfaces thoroughly, and apply a fresh application of new TIM.

Note 4: Thermal adhesive is a specific type of TIM used to permanently or semi-permanently glue heatsinks to devices that have no other heatsink mounting mechanism. Thermal adhesive is NOT intended to be used between a CPU and the CPU heatsink.

Note 5: TIM is also used to ensure maximum heat transfer to the heatsink from graphics processor units (GPUs), chipsets, graphics card memory modules, and other devices. Adhesive TIM, as mentioned in the note above, is often used on these devices as many do not have mounting brackets or holes to support a clamping mechanism. When mounting a heatsink to one of these components, the idea is the same; apply as thin a layer of TIM as possible, while still ensuring complete coverage.

See Benchmark Reviews 33-Way TIM Comparison or TweakTown TIM Review for additional information.
***********

Edit History
12/16/10 - clarified size of a "drop" - Digerati
12/16/10 - Added recommended TIM - Digerati
11/15/10 - Minor formatting edits - Digerati
3/22/09 - Minor edits - Digerati
9/20/08 - Added Benchmark Review link - Digerati
4/22/08 - Added note concerning using TIM with other devices, such as GPUs - Digerati
1/19/08 - Added reference to MX-2 and tweaked text throughout - Digerati
11/17/07 - Added reference to Tuniq TX-2, removed reference to AS Céramique - Digerati

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#2
Gabriel1

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Thanks, Very informative. Just a question, if one has purchased a refurbished or used computer would you suggest applying your own new coat of TIM or letting it run on its own?
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#3
Digerati

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If you have been using it, and your temps are fine, then I would leave it. Contrary to what you might have read, TIM does not just go bad, dry or wear out, as long as the cured bond between the mating surfaces has not been broken.
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#4
Gabriel1

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If you have been using it, and your temps are fine, then I would leave it. Contrary to what you might have read, TIM does not just go bad, dry or wear out, as long as the cured bond between the mating surfaces has not been broken.


I see... again.. informative >_< I actually believed that TIM does dry or wear out. Thanks a lot :D

Just one more question actually, what can be categorized as "too much" TIM? when i purchased a heatsink on my last PC build, it had a rather thick coating of TIM on it, could be compared to maybe cream cheese on a bagel. i decided to remove half of it then use the remaining half to spread it around... Good idea or bad idea?
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#5
Digerati

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I actually believed that TIM does dry or wear out

No it doesn't - again, as long as the cured bond is not broken. So if you remove the heatsink after the TIM has cured, you need to replace it. If you bounce your computer too hard during transport, that too may cause the heavy heatsink to break the bond. If you twist the heatsink to see if the clamps are tight, you may break the bond. But, again, if the bond is not broken, you are okay. It is not like the stuff evaporates when fresh air can't get in and again, the purpose is to fill the pits and valleys so heat trapping air does not get in. If left undisturbed, TIM can easily and does last 10 years or longer - which is longer than most computers survive, and likely more than the CPU's fan bearings will last. And if the fan goes, the whole HSF assembly is generally removed, thus requiring a new application of TIM.

New heatsinks typically have TIM "pads" on them, which are very thick. As noted in Note 2 above, they consist mostly of paraffin and when the CPU is fired up the first time the paraffin quickly melts and the tension of the heatsink mounting clamps squishes the excess out. As noted above, when applying your own, you want the applied layer to be as thin as possible while still providing complete coverage. Remember, the best heat transfer occurs with direct metal-to-metal contact so again, any excess TIM is in the way. Some folks use a stiff credit card to spread it. Others have used a razor blade but I advise against that as razor blades are made of hardened steel and can easily scratch Grand Canyon sized valleys (microscopically speaking) in the aluminum CPU die's mating surface.

As for you removing half being a good idea or not, only you can answer that. Do you still have complete coverage? And most importantly, are your temps good? If so, then it was a good idea.
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#6
Spyderturbo007

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Just to throw in my own experience with TIM. A friend called me because his machine was randomly shutting down, which I immediately attributed to an overheating problem. I cleaned out the machine with some compressed air which brought the temps down a little, but they were still high. I decided to pull off the heat sync because although the overall system temperature dropped, the CPU was still running in the neighborhood of 60 degrees Celsius (140F). I cleaned off all the old TIM and applied some Arctic Silver 5 according to the directions on their website and reinstalled the heat-sync. I booted up the machine, fired up a CPU stress program and let it run for a little while. To my shock, the temps were steady and had dropped to around 100 degrees Fahrenheit. That's almost a 40 degree drop! :D He has yet to encounter any problems.

So, as Digerati said, TIM is a very important part of keeping your machine running well and staying cool.
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#7
Ferrari

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Nice Digerati.


Application: Apply one "drop" of paste, about the size of a grain of rice, on the corner of the die and spread it out across the die with the applicator, like spreading icing on a cake. Spread the paste as thin as possible while ensuring complete coverage. It is easier to add more than remove excess. Remember, too much is counterproductive.

Dead on. An to emphasize even more, you are basically filling microscopic holes, abrasions, scatches, etc. Though to the human eye your heatsink or cpu may appear smooth and even mirrored, under a microscope it kind of looks like grass (very rough). The whole idea is to make the contact between the cpu and the heatsink 100% instead of say 99.5%. It doesn't seem like much, but leaving air in those pockets or gaps makes a tremendous difference. But you don't want an actual separate layer of TIM either.

Good idea to have this pinned!
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#8
RESBAK

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When I apply thermal paste, I usually put a drop in the middle of the cpu and squish it with the heatsink. Is spreading it around with a credit card more effective?
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#9
Amst3rDamag3

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When I apply thermal paste, I usually put a drop in the middle of the cpu and squish it with the heatsink. Is spreading it around with a credit card more effective?

I don't want to get in the way of the TECH here..,
But YES, spreading it out gives you more control over thickness / amount / even spread, especially in the corners.

Also, the TIM I use is Dielectric (some are not, I believe they are the Ceramic ones, but I could use some TECH feedback on that :unsure: ), meaning it conducts electricity, so you would NEVER want it anywhere else except between a cpu/gpu/chip and the heat-sink itself, especially not on the mobo or other bare circuit-board, like the edges of a cpu...

The temperatures will tell the story, if nothing is over-heating, everything is OK, TIM-wise at least.

@Digerati; once again A GREAT GUIDE !!! :)
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#10
Digerati

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Sorry, RESBAK, I was not notified of any responses to this thread and only by chance noticed Amst3rDamag3's.

But I agree, spreading it first is better for the reasons mentioned. But also, it is surprisingly easy to totally crush and destroy a CPU by pressing too hard on it, or pressing unevenly. They can crush just clamping down a heatsink assembly if not careful. And pressing down on the CPU also puts undue flexing forces and stress on the motherboard - never good. Plus, with the heatsink in place, you cannot see if the TIM disburses evenly. By spreading it around with the hockey stick applicator, there's no chance of using too much force, and you can see what you are doing. Some recommend using a razor blade to spread the TIM super thin and I agree 100% that is very effective. But one tiny slip with a hardened steel razer blade can slash a Grand Canyon sized gash with heaved up edges into a CPU die. That would not be good.

meaning it conducts electricity

Ummm, no. That's not right at all. A dielectric is an insulator and dielectrics refers to the polarization of electrons, not conduction. In fact, dielectric compounds are often used with sparkplugs to seal out the environment without creating a conductive path. Most dielectrics are mostly silicon, used intentionally to insulate something from excessive heat, NOT conduct heat. They even make baking dishes out of it that you can grab right out of the oven without burning your hand.

And dielectrics are often used between the mating surfaces of dissimilar metals for the sole purpose of preventing direct contact thus preventing a galvanic reaction and electron flow, thus minimizing the chances of corrosion developing. This means it is often thick (very high viscosity) and the molecules are like boulders (microscopically speaking).

Remember, the best transfer of heat between the heatsink and the CPU occurs with direct metal to metal contact of the two surfaces. The TIM is only supposed to fill the tiny pits and valleys that might trap insulating air. Any more is in the way. So good TIM must have a low (but not too low that it runs like water) viscosity to spread super thin, and super tiny molecules to fill the smallest pits and valleys.

Remember, Google is your friend.

I would not use dielectric compound on CPUs, unless specifically designed for that purpose and even then, if that was all I had. Most dielectric compounds are plain old silicon grease - about the most basic TIM (besides those paraffin pads) you can get.
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#11
Amst3rDamag3

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Google is my buddy :)

I studied mechanics and not electronics... :unsure:
I actually thought that the dielectric material conducts across a surface, generating a field that in turn *edit: electrically* insulates the two surfaces it is separating.
But to keep it simple, I used this stuff from Cooler Master a year (or longer) ago and I wouldn't want it on my circuit board...

Thanks for explaining!

Edit: spelling...
Edit 2: specification...

Edited by Amst3rDamag3, 20 August 2011 - 09:40 AM.

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#12
Digerati

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I actually thought that the dielectric material conducts across a surface, generating a field that in turn insulates the two surfaces it is separating...

And when the goal is to have maximum conduction, why do you want to insulate? You don't care about electrical conduction between the mating surfaces, and if you have so much it squirms out onto the socket or motherboard, you used way too much!

All TIM has dielectric properties, but "dielectric grease" is not TIM, unless it specifies it was made for that purpose. Basic dielectric grease is just used to smear on battery terminals, spark plugs, and other devices to keep out moisture, dirt and debris, and to prevent oxidation and corrosion.
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#13
Akabilk

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Hi Digerati,

I'm about to start another PC build and in the case of Arctic Silver 5 (what I regularly use) I'm wondering why the manufacturers recommend various ways of applying their product, depending on exactly what CPU one is using. I personally use AMD CPU's but have built Intel rigs too.

For almost all AMD CPU's the "center drop" methods is advised (spread method for Laptops), but not so with Intel CPU's. Center drop for a few of their CPU's, but mostly the spread method and for a few the "center line" method.

I have always used the "center drop" method that seems to work well, but I was surprised by the varying Intel advice instructions. I guess it is all about single/duel/multi-core placements or maybe AMD have a flatter surface with less of those micro pits that need filling?

See Arctic Silver Instructions here: http://www.arcticsil...om/methods.html

Cheers,
Lee (wtt)

Edited by Akabilk, 01 October 2011 - 01:38 PM.

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#14
Digerati

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or maybe AMD have a flatter surface with less of those micro pits that need filling?

No, both are as flat and pit free as possible. The thought process with the drop or line method is the forces applied when the heatsink is clamped in place will cause the TIM to spread under the pressure. It also means the user can get in and get out without risking scratching either of the surfaces, or causing damage from ESD. All I see with either a dot or line is a big blob of TIM. So for me, if I have room to get in there, I will still spread it around to ensure a thin, and uniform coverage.
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