Junction Temperature Console

Junction temperature is the single number that decides whether a chip runs or throttles, and the beautiful thing is how simply it's governed. Heat behaves like current and temperature like voltage, so the path from the silicon to the air is just a chain of resistances in series, and the temperature rise across the chain is the power (the ‘current’) times the total resistance. Junction temperature is ambient plus that rise: Tj = Ta + P × Σθ. That's Ohm's law for heat, and it's exact.

The chain has three links you control to different degrees. The junction-to-case resistance is fixed by the package — the chip vendor's problem, not yours. The case-to-sink resistance is the thermal interface material, a thin but critical layer where a bad choice can cost tens of degrees. And the sink-to-ambient resistance is the cooler, usually the largest term and the one you most directly choose — which is why moving from air to a liquid cold plate, slashing that resistance, is the most powerful thermal lever available.

Because the resistances add, the chain is only as good as its worst link. A magnificent cold plate is wasted behind a thick, cheap thermal pad; a superb interface material can't save an undersized heatsink. This is why thermal design is holistic — the package, the TIM and the cooler are co-designed, and the rise-per-resistance breakdown in this console shows you exactly which link is costing you the most degrees, so you spend effort where it pays.

Two cautions. Ambient is one-for-one: a design comfortable at 25°C can fail at a 40°C datacenter inlet, so always check the worst-case ambient. And this is a steady-state model — correct and conservative for sustained AI workloads, but bursty loads need transient analysis. Bring the interface resistance from the TIM Calculator, and for parts with concentrated hotspots, complement this with the Power Density console.