The thermal wall, quantified

Set a chip's power and die area. The tool computes the heat flux the package must remove and a footprint-referenced effective conductance requirement, U″ = Q / (A_footprint·ΔT_{junction−coolant}). This is not the local fluid-side coefficient h: real cold plates wet far more area than the footprint, while only part of the temperature budget falls across the convective film. The h bands below are physical reference scales — the harder your U″ presses against them, the more area multiplication and stack engineering the design must buy.

Model: the tool reports a footprint-referenced effective conductance requirement, U″ = Q/(A·ΔT), computed on the package footprint with the full junction-to-coolant budget. It is not the local fluid-side heat-transfer coefficient h unless the wetted area equals the footprint and the entire ΔT falls across the convective film; real systems have wetted areas larger than the footprint (lowering the required local h) and conduction and interface losses inside the stack (raising it). The h bands (natural convection ~5–25, forced air ~25–250, single-phase cold plates ~1–20×10³, microchannel ~2–10×10⁴, boiling ~0.3–1.2×10⁵ W·m⁻²·K⁻¹) are reference scales for orientation in this simplified model, not pass/fail thresholds for any architecture.