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Thermal Interface Material

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#1 Digerati


    Built, broke, fixed, learned.

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Posted 01 June 2009 - 07:12 AM

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 absolute best transfer of heat occurs with direct, surface-to-surface contact between perfectly flat mating surfaces, clamped together with optimal pressure uniformly applied by the heatsink mounting mechanism. It is safe to assume the Intel and AMD supplied cooling solutions provide the required mounting pressure. But unfortunately, it takes too long and is too expensive to properly "lap" CPU and heatsink mating surfaces. While today's machining capabilities are very precise, there will still be some microscopic pits and valleys in the CPU die and heatsink mating surfaces.

The purpose of TIM is to fill all those microscopic pits and valleys to push out any trapped, insulating air, maximizing heat conduction. Any excess TIM is too much and gets in the way and can actually be counterproductive to the heat transfer process. It is critical not just to use TIM, but to apply it properly too.

The 5 Most Common Heatsink Fan (HSF) Assembly Mounting Mistakes:
  • Failure to use TIM,
  • Used too much TIM,
  • Reused old TIM,
  • Failure to clean mating surfaces thoroughly before applying TIM,
  • Failure to ensure heatsink mounting clamps were securely fastened.
Reusing old TIM and failure to clean properly often go together to create a worse problem. It is essential to never reuse TIM once it has cured (got hot and cooled during at least one power cycle). If the cured bond breaks, you must assume air has entered gaps, compromising the TIM. The old TIM must then be thoroughly cleaned from both mating surfaces, and a fresh new layer of TIM needs to be applied.

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, Noctua NT-H1 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 primarily of very pure, fast melting paraffin which melts and squirm out of the way when the CPU heats up for the first time, leaving just the TIM behind. The Intel and AMD OEM thermal pads are quality pads, perfectly suited for the vast majority of users. I cannot say that for aftermarket pads, though they are certainly better than no TIM at all. 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: TIM does not wear out, dry out, breakdown or need to be replaced regularly unless the cured bond has been broken due to heatsink removal, twisting (often too hard when check to see if tight), rough case handling, or transport. TIM easily lasts and remains effective for 10 years or longer, if the bond remains in tact.

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 80-Way TIM Comparison or Nerd Techy 5 Best Thermal Paste for 2017 - 2018 for additional information.

One final word. It is important to remember it is your case's responsibility to provide adequate flow of cool air through the case. If there is no reason the cured bond was broken and your temperatures are higher than normal, look at dust build-up, resource (CPU and RAM) utilization/malware, case cooling/fans, and ambient (room) temperatures first, before replacing the TIM. If the 5°C you get from advanced technology TIM is that critical to CPU stabilization, there are other heat issues to deal with first.


Edit History

3/8/2018 - updated links and minor edits - Digerati
2/10/17 - Updated Review link - Digerati
8/7/16 - Updated links and minor edits - Digerati
1/13/16 - Updated links - Digerati
11/14/15 - Updated recommeded TIM
8/3/12 - Expanded reusing TIM and cleaning surfaces comments -Digerati
8/1/12 - Updated TIM review data - Digerati
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

Edited by Digerati, 08 March 2018 - 12:17 PM.

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