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Silicone-based vs. liquid metal thermal compound

We take a look at the differences between silicone-based and liquid metal thermal compounds and how to use them for maximum performance.

Anyone who has ever built a PC has encountered the question: What is the best method to apply thermal compound on the CPU? The cross method? Just a pea-sized blob in the middle? Maybe you have attempted to evenly distribute it with a spatula or credit card?

And while we might not have the answer to this question in this article, we prepared a video in which we compare the most common methods. It also shows the correct application of liquid metal thermal compound!

Right now and here, we answer the other, more important one pertaining the liquid metal:

What is liquid metal thermal compound and when should I use it?

Thermal pastes are often referred to as thermal compound, thermal grease, or thermal interface material (TIM). Thermal paste sometimes comes pre-applied to a CPU cooler’s base, or in a separate syringe. While thermal pastes also have applications outside CPU cooling (for example, GPU cooling), we will focus on replacing the TIM with CPUs, as that is much more accessible to everyone. 

While the surface of a CPU heat spreader looks smooth from afar, under a microscope it can easily be mistaken for the surface of the moon, full of craters and imperfections.

These blemishes are unavoidable due to production processes, and they trap air when 2 surfaces are pressed onto each other with no filler material. Since air is an insulator, it is the highly heat-conductive thermal paste’s job to compensate for the imperfections and assure even heat dissipation over the largest possible surface area. 

The most common and often pre-applied thermal compounds consist of silicone oil and zinc-oxide as base components. High-performance offerings are enriched with aluminum, silver, copper or even diamond particles.
This is to improve heat conductivity and garner maximum performance. Silicone-based thermal paste, like the be quiet! DC2, can be used with any CPU cooler and processor. It is easy to apply, easy to remove, safe to use, and for most users this will be the preferred method of use.

Liquid metal thermal compound has much higher thermal conductivity.

As an example, the be quiet! DC2 Pro liquid metal TIM has a conductivity of 80 W/mK (watts per meter-Kelvin), while the silicone-based DC2 only features 7.5 W/mK. It works the same way silicone-based pastes do, but thanks to the higher conductivity, liquid metal users can squeeze the last bit of performance out of their cooler and, by extension, their CPU. Overclockers often even remove the integrated heat spreader (IHS) of the CPU and apply the TIM directly to the die. This process is called delidding and since liquid metal TIM is more conductive than the default IHS, it yields even better results than applying the paste on the heat spreader. It goes without saying that delidding a CPU voids the warranty and should only be attempted with proper tools and by advanced and experienced users only.

However, this is not without risk. Under no circumstances can liquid metal thermal paste be used with heat spreaders or cooler bases made of aluminum.

Common ingredients of liquid metal TIM, gallium and indium, cause a heavy chemical reaction with aluminum and the light metal will become brittle. Using liquid metal compounds with copper is possible, but the TIM may diffuse into the copper and a second application may be necessary. The best use-case for liquid metal is in combination with a nickel-plated cooler base, where the nickel layer protects the base plate but is also highly heat-conductive. 

Liquid metal thermal compound does not only conduct heat, but also electricity very well. It goes without saying that replacing any component in a PC should only be done after disconnecting power to the system; however any residue of liquid metal that may have made its way onto the motherboard needs to be carefully removed before power is restored. After application and installation of the cooler, the liquid metal hardens and forms an efficient heat dissipation layer.

For removal, the TIM should be wiped with a dry paper towel, followed by a towel with a cleaning agent (like isopropyl alcohol). The added maintenance is the reason why liquid metal thermal compound is recommended for advanced users only. However, we hope that you have learned about this process and understand that with the right application, your CPU cooling can experience a significant boost.

From the current be quiet! cooler portfolio, the following models are recommended for use with liquid metal thermal compound, like the be quiet! DC2 Pro:

-    Silent Loop 2
-    Pure Loop 2 FX
-    Pure Loop 2
-    Pure Loop
-    Dark Rock TR4
-    Dark Rock Elite
-    Dark Rock Pro 5
-    Dark Rock Pro 4
-    Dark Rock 4
-    Dark Rock Slim
-    Dark Rock TF 2
-    Shadow Rock TF 2
-    Shadow Rock LP

One last piece of advice:

Always check if the protective sticker foil was removed from the base plate, if the thermal paste is not already pre-applied.