Framework Laptop 16 Deep Dive - Liquid Metal with modifications for Phase Change
When we first shipped Framework Laptop 16, we leveraged a fairly complex liquid metal thermal interface for the CPU to maximize performance. After long term usage, we found that some systems in the field faced performance degradation. After root causing this issue as the liquid metal formulation gradually pumping out of the CPU area over hundreds of thermal cycles on some units, we started investigating thermal solutions with more consistent long term performance reliability. We landed on Honeywell PTM7958 phase change thermal interface material as the best solution. This is a material that has been popular in the Framework Community for years, and our testing confirmed that it both performs excellently on initial application and continues to behave robustly over thousands of thermal cycles. With this, we’ve switched our ongoing production of Framework Laptop 16 systems and Mainboards over to the Honeywell material. In early 2025, we’ll also be making phase change material kits available in the Framework Marketplace and providing them to existing customers who have faced performance degradation.
Original blog post
The Ryzen 7040 Series processor in Framework Laptop 16 is capable of running at a sustained 45W TDP (Thermal Design Power) and we put together an excellent thermal solution to ensure it can do that while keeping CPU temperature, touch temperatures, and fan noise to a minimum. That 45 watts of CPU power needs to be efficiently conducted into the vapor chamber, heatpipes, and fins to be carried away through airflow from the fans. Since neither the CPU die nor the vapor chamber surface are perfectly flat, a thermal interface material is needed to fill in gaps to avoid comparatively insulative air taking up that space. Traditionally, most computers use a thermal grease that has thermally conductive particles suspended in silicone. This works reasonably well, but the silicone itself isn’t especially thermally conductive, and the paste can pump out or dry out over time, making it less effective.
Instead, on Framework Laptop 16, we used a liquid metal thermal interface on the CPU. Liquid metal is exactly what it sounds like: a 100% metal sheet made up of indium, tin, and bismuth that turns from solid into liquid at around 58°C as the CPU heats up, filling any air gaps completely. Being metal, it is extremely thermally conductive, rated at 72W/mK, substantially better than the 5-10W/mK that is typical for traditional paste. It also doesn’t dry out or pump out over time. We’re using Coollaboratory’s Liquid MetalPad through their Taiwan-based partner CCHUAN.
You might be thinking, is it safe to have highly electrically conductive liquid inside of a portable device? The answer in this case is yes, as we’ve designed the thermal system to contain it at multiple levels. First, because AMD’s processors have small capacitors directly next to the CPU dies, we dispense an insulative glue layer using a robotic fixture during Mainboard assembly to cover them. Next, an etched pattern in the surface of the vapor chamber holds the liquid metal through tension. Finally, a dual foam barrier around the CPU is squeezed between the processor package and the vapor chamber copper plate, preventing any liquid metal from escaping. All of this results in a very cool thermal solution and great CPU performance.
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