Calculation method and supported range
Rθ = thickness/(k × area), with thickness in metres and area in square metres. Returned resistance is kelvins per watt (equivalent to °C/W for temperature differences).
Uniform steady one-dimensional conduction only. Omits heat spreading, vias, copper planes, contact resistance, convection, radiation and heatsinks. It does not predict device junction temperature.
Technical sources
Using the result
Use the cross-sectional area of the actual heat path and the through-plane thermal conductivity. The model excludes spreading, interfaces, convection and thermal vias. A layer resistance by itself cannot predict junction temperature or qualify a power-amplifier thermal design.
From a calculation to a released design
Keep the input assumptions with the result. Recalculate when the ordered material, dielectric height, copper or operating conditions change. Confirm the final construction with the fabricator and use field simulation or measurement wherever the simplified model omits an important effect.
See the controlled-impedance guide and material selection workflow for the next checks.