Insulated metal substrate heat pathHeat must reach the cooling systemConceptual section · not to scale · electrical isolation is part of the designComponentCircuit copper — carries current; spreads heat locallyDielectric — insulates electrically; conducts heatMetal base — aluminum, copper or specified steelTIM / mounting contact — an additional resistanceHeat sink — rejects heat to the surroundingsRlayer = thickness / (conductivity × effective heat-flow area)A better base alone cannot remove dielectric, interface or heat-sink resistance.