What Is a Phase-Change Thermal Pad and How Does It Work?

Thermal pads and paste are integral parts of our computers’ cooling mechanisms. We’ve seen various iterations of those materials over the decades. A recent development in the field has emerged, and what’s exciting is that it leverages a physical process called “phase change.”

What Are Phase-Change Thermal Pads?

A Phase-Change Material (PCM) is a substance that can store and release heat as it transitions from one physical state to another. In the context of computers, PCM thermal pads that change from a solid to liquid could be used as an alternative to conventional Thermal Interface Materials (TIMs) like thermal paste. The change happens at slightly above room temperature, making it suitable for use in consumer electronics.

For the context of this article, we’ll mostly focus on the Honeywell PTM7000 Series, a non-conductive material intended for industrial use for power control units, inverters, and in the automotive industry, but some enthusiasts actually use it to keep their electronics cool. ​​​​​One other promising PTM is gallium, a metal with a melting point of 85.58°F (29.76°C). Alienware uses gallium (Element 31) in a few of their high-end laptops, like the Alienware X15 and X17.

Phase-Change Thermal Pad vs. Thermal Paste: When to Use Pads

PTM thermal pads could be an excellent alternative to conventional thermal paste. Honeywell claims that their PTM7000 Series has a thermal conductivity of around 6–8.5W/mK (Watts per meter Kelvin), which is at the level of high-end thermal paste. It’s still a far cry from liquid metal’s thermal conductivity of up to 73W/mK, the “ultimate solution” for enthusiasts who don’t mind putting their components at risk.

Linus Tech Tips put up the Honeywell PTM7950 pad against the highly regarded Noctua NT-H2 thermal paste and Thermal Grizzly Conductonaut Liquid Metal. Once the PTM7950 had a chance to phase-change (melt), it performed about as well as the Noctua NT-H2. In fact, the difference between the three was insignificant.

Now, before you run out to procure some PTM7950, you should know that it’s hard to find a genuine Honeywell thermal pad, and it can cost a lot more than high-end thermal paste for just a single application.

The main advantage of PTM7950 is that it can perform at an optimal level for over a decade, whereas even the best thermal paste will dry out and have reduced performance after a couple of years. Honeywell has thoroughly tested the PTM7000 by alternating between -55°C and 125°C for 1,000 cycles. The shocking result is that the PTM’s thermal impedance actually dropped after the test, which means that the material performed even better.

PTMs are an amazing thermal solution by all accounts—provided they come pre-installed by the manufacturer. Another use case is if you’re an enthusiast who wants a more permanent solution without risking it all by using liquid metal. For everybody else, thermal paste is still more convenient, cheaper, and easier to apply.

Some Manufacturers Are Already Using Phase-Change Thermal Pads

I’ve already mentioned Alienware laptops above, which use gallium, but Redditors have found evidence that suggests some Lenovo Legion laptops use Honeywell PTM7958 pads, an optimized version of the PTM7950. MSI has done something similar as well—MSI uses phase-change metal pads that essentially turn into liquid metal when heated.

The prospect that these developments present is thrilling. If manufacturers adopt PTMs and pre-apply them on products like CPU coolers and graphics cards, we could finally stop having to tear apart our expensive toys to get small cooling improvements associated with high-end thermal paste.