How would you develop a multi-scale thermal model for an electronic system from chip to enclosure level?

Multi-scale approach: Chip level (μm-mm) - detailed power maps from electrical simulation, spreading resistance in die/TIM/IHS, compact thermal models (Delphi-style CTMs) with 3-10 nodes representing key junctions; Package level (mm-cm) - detailed 3D FEA including leadframe/substrate/solder, validated against thermal test chips (JEDEC standards), boundary condition sensitivity analysis; Board level (cm) - PCB as orthotropic material (in-plane 30 W/m-K, through-plane 0.3 W/m-K), component interactions via radiation and board conduction; System level (m) - coarse CFD with components as volumetric heat sources using CTMs, fan curves and vent impedances. Each level provides boundary conditions for detailed models and validates against measurements. Key challenge: information transfer between scales maintaining accuracy while managing computational cost.