We spent months obsessing over the thermal design of Umbrel Pro. 8-core CPU, iGPU, 4 NVMe SSDs, tiny form factor, whisper quiet, toolless SSD access. Here's how we pulled it off 🧵

To achieve this form factor we use a double-sided PCB. CPU/GPU on top. Four M.2 SSD slots on the bottom. All cooled by a single low-profile fan. In a case small enough to sit on your desk.

However magnetic aluminium lid isn't just a lid, it's a massive heatsink. Lift it off in one smooth motion to access your SSDs. Close it and thermal pads make direct contact with the top of all four drives. <lid removal showing thermal pads, SSD contact>

But it gets better. The lid has air intakes carved out of its internals.

Air gets sucked in to the lid vents, passes through the lid internals, flows into the SSD chamber, gets directed through holes behind the SSDs, enters the CPU chamber, gets pulled through the CPU fan, exhausted out the back. One continuous airflow path. No dead zones. <image or potentially 3d animation of full air flow>

So the aluminium lid is both passively cooled on the outside and actively cooled on the inside. While the top of the SSDs make direct contact with the lid and the bottom of SSDs are cooled by active airflow. Every surface is working together to maximise cooling efficiency.

Another challenge is that different SSDs have wildly different operating temperatures. Umbrel Pro reads each drive's thermal limits and dynamically generates a custom fan curve to keep them all in the safe zone.

But how can we manage five independent thermal zones with a single fan? We sample all temps continuously, evaluate all fan curves simultaneously, and apply only the single highest value. One fan. Perfectly managing 5 components.