Definition

Thermal conductivity measures heat transfer through a material (W/m·K). Standard FR-4: 0.3 W/m·K (poor). Aluminum: 205 W/m·K. Copper: 385 W/m·K. For PCBs, heat conducts through copper (traces, planes, vias) much better than through dielectric. Thermal vias transfer heat between layers. Metal-core PCBs use aluminum or copper for heat spreading. High-power designs need thermal analysis - component junction temperature depends on thermal path to ambient. Some specialty materials (ceramic-filled, aluminum nitride) offer improved thermal conductivity at premium cost.