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Thermal Paste Application Techniques

Thermal Paste Application Techniques

Written on November 12, 2012 by Matt Bach

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Warning: Always look at the date when you read a hardware article. Some of the content in this article is most likely out of date, as it was written on November 12, 2012. Check out our more recent articles.

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 potions 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

 



Share this article!

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
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