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Thermal Paste Application Techniques

Written on November 12, 2012 by Matt Bach
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Table of Contents:
  1. Introduction
  2. Test Setup
  3. Application Techniques
  4. Spread Results
  5. Temperature Results
  6. Conclusion

Introduction

No man-made surface is perfectly smooth, and the tiny gaps between a CPU and a heatsink are usually large enough to have a negative impact on cooling. To combat this, thermal paste is used to fill in these air gaps. The thermal paste itself is not as thermally conductive as metal, however, so it is important that not too much is used. If that happens, the thermal paste will behave more like an insulator than a means of improving thermal performance.

Heatsink air gap

The best technique to apply thermal paste is something that is often debated on the internet, so in this article we want to do our own testing to find the best method for applying thermal paste. First we will see how each technique spreads the thermal paste across the CPU, and then we will test each technique in a full computer system to see which has the best thermal performance.

Test Setup

To get a clear view of how the thermal past spreads for each technique, and to see if the spread results in any air bubbles, we fabricated a 3/8" thick acrylic plate to act as an interim heatsink. This acrylic plate has portions removed to clear the capacitors around the CPU, and the mounting is the exact same size and spacing as the Corsair H60 CPU Cooler. This way, we can ensure that our results match exactly what you would see when using a real heatsink.

Thermal Paste Spreader Top Thermal Paste Spreader Bottom
Top of the acrylic heatsink analog Bottom of the heatsink analog
Thermal Paste Spreader In Place Thermal Paste Spreader Secured


For our thermal testing, we will be using the following components:

Testing Hardware
Motherboard: Asus P8Z77-V Pro
CPU: Intel Core i7 3770K 3.5GHz
CPU Cooler: Gelid Tranquillo Rev2
RAM: 2x Kingston DDR3-1600 4GB
Video Card: Intel HD 4000
Hard Drive: Intel 320 120GB SSD
Chassis: Open Air Test Bench
Thermal Paste: Arctic Cooling MX-2
Thermal Paste Testing Station


CPU temperatures were recorded with a combination of CoreTemp and Speedfan with the temperature reported as the average of the four cores. We let the system idle for at least 45 minutes before recording the idle temperatures, and to put the system under 100% load we ran a combination of both Prime95 and Furmark. Dynamic fan ramping was disabled from the motherboard since we are primarily concerned about the variances in temperature between each application technique and do not want the fan throttling to affect our results.

We are using the built in video controller to help put just a little extra load on the CPU which should accentuate any temperature variances. An open-air test platform was used in place of a chassis since it should allow for more consistent results.

Application Techniques

The techniques we are testing come from the common recommended techniques found online as well as a few we devised ourselves. We made sure to apply the paste evenly, but did not make it 100% perfect. We did this on purpose so that our results would be consistent with what you would see in the real world.

Thermal Paste Rice sized dot Thermal Paste 2x rice sized dot Thermal Paste thin line
Rice sized dot in the middle 2x rice sized dot in the middle Thin line across the middle
Thermal Paste thick line Thermal Paste Three thin lines Thermal Paste spiral pattern
Thick line across the middle Three thin lines Spiral pattern
Thermal Paste rough spread Thermal Paste smooth spread Thermal Paste X shape
Roughly spread across CPU Smoothly spread across CPU X shape
Thermal Paste circle shape Thermal Paste circle shape with dot Thermal Paste happy face
Circle shape Circle with dot in the middle Happy face


Each of these techniques (with the possible exception of the happy face) have some merit to them. The single dot or line should have few air bubbles, but likely will not cover the entire CPU. At the same time, the spiral pattern will likely cover the entire CPU, but may have some air bubbles. To find out, let's take a look at how each technique looked after installing our acrylic heatsink stand-in.

Spread Results

It is almost impossible to see the tiny air bubbles in the images below, so we went ahead and circled them in blue. Larger air bubbles have larger circles, while smaller bubbles have smaller circles. Similarly, any areas where the thermal paste did not cover the CPU are circled in red.

Thermal Paste Spread - Rice sized dot Thermal Paste Spread - 2x Rice sized dot Thermal Paste Spread - Thin line
Rice sized dot in the middle 2x rice sized dot in the middle Thin line across the middle
Thermal Paste Spread - Thick line Thermal Paste Spread - Three thin lines Thermal Paste Spread - Spiral pattern
Thick line across the middle Three thin lines Spiral pattern
Thermal Paste Spread - Rough Spread Thermal Paste Spread - Smooth spread Thermal Paste Spread - X shape
Roughly spread across CPU Smoothly spread across CPU X shape
Thermal Paste Spread - Circle shape Thermal Paste Spread - Circle shape with dot Thermal Paste Spread - Happy face
Circle shape Circle with dot in the middle Happy face


The first thing to point out is that the single dot and line had almost no air bubbles, but they did not spread across the entire CPU. Even doubling the size of the dot still did not cover the entire CPU as the majority of the extra thermal paste simple squirted out the sides. Using three lines instead of one helped with coverage, but resulted in more air bubbles.

Both roughly and smoothly spreading the thermal paste across the CPU had great coverage, but resulted in quite a few small air bubbles. These air bubbles are tiny compared to the circle and spiral shapes and likely to have a minimal effect on performance, but they are definitely present. Spreading the thermal paste perfectly should result in fewer air bubbles, but in our experience it is impossible to get it 100% perfect.

Surprisingly, the X shape resulted in the best overall spread with great coverage and very few air bubbles. This surprised us a bit, but makes perfect sense when you think about it. The X shape allows the paste to spread equally across the CPU, and since the spread is from the inside out, the shape helps prevent air pockets from becoming trapped.

Unfortunately, the happy face did not have great coverage and resulted in a few relatively large air bubbles. But the biggest factor for each technique is how well each actually cools the CPU, so let's take a look at our thermal testing results:

Temperature Results

Thermal Paste Application Technique Thermal Results

Overall, the thermal results are pretty close to what we expected given our spread testing. The X shape, with the best coverage and fewest air bubbles, performed the best at 54.25°C under full load. The smooth spread was close behind and was only .25 °C hotter under full load. Surprisingly, the rice sized dot tied with both the happy face and the circle with dot for third place at 54.75 °C.

Interestingly, the 2x rice sized dot and thick line - both of which had quite a bit of excess thermal paste that got squeezed out from between the CPU and the heatsink - did the worst in the thermal testing. This reinforces the idea that, just like too little thermal paste, too much thermal paste can result in sub-standard performance. 

Conclusion

Thermal Paste ApplicationFor years, we at Puget Systems have used either the rice sized dot or the smooth spread technique in our builds depending on the system requirements. Smoothly spreading the thermal paste takes time and effort to get exact, however, so the fact that our testing shows a simple X shape performing even better is absolutely great news. Not only is it a much simplier application technique, it is also much easier to keep consistent. And for those that are wondering, it works just as well on larger CPUs like the Intel socket 2011 CPUs. The thickness of the line just needs to be very slightly increased, and the X shape should be extended to cover the entire face of the CPU.

Perhaps our most interesting result is that if you are going to use the tried-and-true rice sized dot, you might as well have a bit of fun and draw a little happy face instead. Not only does it cool just as well, but you can rest easy knowing that you have a happy, smiling CPU underneath your heatsink.

 

Best Performance:
X Shape

Thermal Paste best application technique

Tags: CPU, Cooling, Performance, Advice, Temperature, Thermal Paste

What would be the most optimal amount of paste and spread method for a processor without an integrated heatsink? For instance, a laptop processor with just the die coming into contact with the base of the heatsink?

Posted on 2012-11-13 02:43:56

For something like that, I would use the smooth spread method. Getting perfect coverage on a non-square shaped die is going to be difficult unless you do the spreading yourself. If you are unsure if the coverage is good or not, it's usually a good idea to apply the thermal paste, install the heatsink, then remove the heatsink and see how well it spread. Check that the entire die is covered and that not too much was pressed out the sides. You will want to clean off the die and heatsink and reapply the thermal paste, but at least you will know for sure if you are using the right amount.

Posted on 2012-11-13 08:52:40

Great test.
But how about a test the other way around. Take different heatsinks and test how they fair with the different metods? Some heatsinks that have the copper tubes directly onto the CPU, have gaps bethween the tubes, which metod is right for that

Posted on 2013-04-01 09:25:53
Vanessa

In other words, as long you use the right amount, any of the tecniques are the same realy. So its up to what one the person has more experience and confort to apply.

Posted on 2013-06-11 07:30:43
James Childress

I think the reason your smooth spread has so much air trapped was because it was not smooth. It had a lot of texture to it. I just installed a cpu today using the smooth method and I took the time to smooth it as flat as possible. The result was a CPU that with the stock cooler was easy to OC about 300 mhz above stock (3.8ghz to 4.1 Ghz) speed and still be within safe operating tolerances.

Posted on 2014-03-01 14:43:40

how to apply the or spread the paste ?? plz elaborate

Posted on 2014-04-30 16:11:04
shane

what did you guys use to torque the heat sink dummy down with? or did the screws have shoulders which allowed them to only tighten to a certain clearance? Also it seemed like a lot of the other shapes could have worked better if they were just applied thicker and had more squeeze out.

Shane

Posted on 2014-07-22 18:38:53
Not Debating -- Informing

This is what Cisco recommends for use on Xeon CPUs in some of their blade servers, so it looks like the X shape is well-regarded.

Posted on 2014-08-07 08:55:02
Darryl Mylrea

The other point that was not mentioned was how much paste the different methods uses. Obviously, the rice grain uses the least paste, and the smooth, "X", other methods use much more (expensive) paste. In a price/performance comparison, the rice grain would offer the best protection for your dollar.

Posted on 2015-01-24 14:53:43
Chris

Quite the contrary, the cost impact of a few extra degrees over several years of running a computer is likely a ton more than whatever amount of 6-10$ paste you might use. In fact, the added burden on your CPU from the heat (and even running extra voltage) affects performance down the line, which is why I rarely overclock. The heat also impacts your motherboard, which in turn also impacts your other parts like RAM, and even the extra case heat can impact things like the video card or hard disks.

Of course, what do I know? I just have the same computer I've had for 11 years, and can play games like Skyrim on high settings with just a graphics card upgrade I did about 5 years ago.

Posted on 2015-09-11 13:20:15

If the X is good, would an asterisk (superimpose + and X) be better?

Posted on 2015-01-27 17:58:36
Josh Trewhella

why does everyone hate on the smooth spread? seems like it performs well.

Posted on 2015-03-15 00:28:19
luka3rd

Great effort! Thank you!

Posted on 2015-05-10 23:29:25
A Bread

This shows really well that less is more! You should put as less as possible on it but still cover the whole surface!
Of course it's hard to know how much is enough to cover the whole surface (exept you use the smooth spread mothode) when you can't see it spreading like in this test, so just make shure you don't use too much like you see with the "Rize dot" and the "2x Rize dot" methode ;)

Posted on 2016-01-02 00:24:01
1Bambinone

You still trust those guys coming into the web and teaching people how to apply the paste. They are crook. Most thermal paste can only dissipate about 3 Wm/k while a metal against metal can dissipate much more heat. Alluminum, for example, dissipate 205 Wm/k, copper dissipate 385 Wm/k. Any paste that does not dissipate heat properly can prevent cooling of the CPU and it will burn faster. If you would turn copper into powder and add it to the thermal paste you would be much safer than going with simple thermal paste. That's life. When you look for chip products they take advantage of your money and cause you conditions to burn your CPU. I remember my Siemens computer that after a couple of year of use lost its graphic card. What did they apply over the graphic card's CPU? The stupid paste right from the factory.

Posted on 2016-02-26 08:23:15
Jan Magne Skaue

No current human tech can manufacture perfectly flat surfaces, and here we're talking mass produced consumer products. Just putting the cooler/block onto the heatspread (direct metal-metal contact) leaves immense amounts of gaps due to surface imperfections. Even if might not be visible to the naked eye, it is most definitely there. Liquid thermal compounds only serve an (extremely) positive function in terms of filling those gaps. Any excess compound beyond that has an insulating effect, so less is clearly more. Its not ideal, but it sums up to a vastly more effective thermal conduction path, than just clamping metal to metal without anytihng to fill those gaps.

Metals (here) are solids. We can grind up those particles pretty small, but they still need to be suspended in something fluid, that /will/ be less thermal conductive. As tiny as possible particles and a perfectly even blend distribution is critical - and us mere mortals don't have access to such equipment. Its simply cheaper to buy a finished product. But there are metal thermal compounds available. They are quite a hassle to deal with, electrically conductive and there is always the chance of galvanic corrosion, depending on heatspread, thermal compound and cooler material. Gains are decent, no miracle - but the product IS available.

Posted on 2016-03-01 17:39:00
h_1995

i'd like to reapply thermal paste for my laptop cpu and gpu. so does the cross method the most suitable? between rice dot and smooth spread which one is better?

Posted on 2016-05-06 09:37:56

For laptops, most of the time the die (where you are applying the paste) is not actually square but is rectangular. Personally, I tend to do just a thin line in that case. The spread is pretty good for a rectangular surface and you shouldn't have any air bubbles. A smooth spread should work fine too, but I wouldn't do just a rice dot (since it likely won't spread across the whole rectangle unless you put way too much on)

Posted on 2016-05-06 17:46:00
cat1092

Maybe I need to redo my notebook that I just installed (upgraded to) a i7-620M, based on this, though mine was square. As always, used the 'rice' size on notebook & pea or oat sized on PC CPU's, and wiggled the heatsink a bit before placing in the screws & tightening, with about 5-6 rounds in a criss-cross pattern. Plus there was the discrete nVidia 425M GPU, often there will be a thermal pad on these, on this model, was pasted. Seems that a GPU, being more fragile, the pad would had been a better idea, as I've had others with these & reused successfully.

Maybe for that purpose, I need to get some of the thermal pad material, however it's distributed, can be cut to size. One thing for sure, one cannot over-tighten the GPU area, otherwise the discrete GPU will crack & will only have the Intel (or AMD) graphics inbuilt into the CPU (or APU). Or a notebook that'll BSOD with every boot.

However so far, the i7-620M has ran at lower temps than the previous i5-480M using MX-4 thermal paste (my favorite) & grab a 4g tube at Newegg when on promo every now & then, doesn't have an 8 year warranty for nothing. Both CPU's runs at 35W and GHz levels are also close to the same, yet the i7-620M doesn't freeze at with a lot running at boot & then opening a browser, unlike the i5. Unfortunately, there were no quad core model for the socket (that I was aware of in the Arrandale M CPU's), and even if it were, more power would be needed, as well as a better heatsink assembly, which also limits notebook CPU upgrades.

Sometimes there's also more than one right answer, as long as the end result is not too much paste, few as possible air pockets, and the CPU is running cooler, that's a sign of success.

However there was one component that temps didn't drop nor raise on, and that was the MB temp itself. Because after 30 minutes of use, Speccy as well as CUPID's H/W Monitor, reports temps between 60 & into the lower mid 70C range. Which for a MB, I feel is kind of high, the notebook was tore down enough to get a good blowing out, and there wasn't much dust at all for a 2011 MSI FX603 purchased new by me early that year. In fact, the initial CPU was released the same quarter I purchased it, so was fresh from the assembly line :-)

Being that the MB has always ran at these temps, I keep it on a cooler in a certain position to blow cooler air through the single intake vent. Maybe I should, being it's long out of warranty, consider a bottom case mod for more air intake? I'm sure there are small round filtered intakes, like those on the side of AMD PC's that has a plastic duct going downwards towards the CPU, that can be used in the part of the case that opens (the access lid), w/out the duct of course. Since there's only one small intake & that's very close to the exhaust, maybe one towards the center (where the GPU is) or opposite side will provide more fresh air to cool the MB?

I'm afraId that no matter how much I can lower CPU temps with the best paste & application method, all will be for nil if the MB is running hot. Maybe it's the discrete GPU causing the MB to run hot, and a vent should be created as close as possible to it. My Toshiba of the same CPU family running an upgraded i5-560M (from i3-370M) doesn't have this issue under normal use, since it runs only Intel HD graphics. Though if I'm running an extended Malware scan both the CPU & MB will heat some, which is normal with notebooks, then cool back down, even w/out a cooling pad. The MSI MB reaches 60C with just casual browsing after 20 minutes & 65-70C when Windows Updates are installing. Speaking of which, the GPU also runs warmer than what I feel to be normal (upper 40's to 55-60C), and the repasting showed no positive (or negative) effect. Makes me wonder if the thermal pad would had been a better choice, if one were on hand?

What do you all think of the ventilation idea? Nothing to lose, other than a bit of time & at most, $10 for a small round filtrated vent w/screws, maybe the size of a 12 ounce soda can end? While I believe MSI has good builds, for what was at the time, an 'upper-mid' gaming notebook at $750, maybe they didn't think much about air intake? BTW, the Toshiba has extra intakes, with grooves in a couple of extra places, on the opposite end of the notebook, under the HDD that now houses an SSD, under the access lid to the RAM & a huge row in the center. No wonder the MB runs 20-25C cooler under normal conditions.

I need to do something, even if it's experimental, the pasting won't cool the MB, which will lead to the demise of an otherwise nice notebook. Had I thought it to be no good, wouldn't had spent $40 for the CPU upgrade.

Cat

Posted on 2016-05-24 23:12:08
Stephen Mitchell

Did you perform these tests on different thermal compounds, and if so did the results corroborate the results using the MX-2 compound?

Posted on 2016-06-08 10:47:50