Heat generated by power components is often concentrated in a relatively small area, while the cooling system operates over a much larger surface. How efficiently this heat spreads before reaching the dielectric, metal base and heatsink can strongly influence local temperature and overall thermal behavior. This article explains the engineering principles behind heat spreading area, heat flux, thermal footprint and spreading resistance, and shows how copper geometry and metal-base construction can be used to create a more effective thermal path in Metal Core PCB design.