I wonder if there could be some way to photolitograph compute circuits directly onto a radiator substrate, and accomplish a fully-passive thermal solution that way. Consider the heat-conduction problem: from dimensional analysis, the required thickness of a (conduction-only) radiator plate with a regular grid of heat sources on it shrinks superlinearly as you subdivide those heat sources (from few large sources, into many, small ones). At fixed areal power density, if the unit heat source is Q, the plate thickness d ∝ Q^{-3/2}. (This is intuitive: the asymptotic limit is a uniform, continuous heat source exactly matched to a uniform radiation heat sink; hence heat conduction is zero). So: could one contemplate an array of very tiny CPU sub-units, grided evenly over a thin Al foil—say at the milliwatt scale with millimeter-scale separation? It'd be mostly empty space (radiator area) and interconnect. It'd be thermally self-sufficient and weigh practically nothing.
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