Begin with heat dissipated under the worst credible RF operating state: measured DC input minus delivered RF output, plus auxiliary losses that cross the same thermal boundary. State the maximum junction, case or baseplate temperature and where it is measured; RF output watts, top-surface temperature and a generic heatsink rating are not interchangeable thermal inputs.
For either air or liquid cooling, define contact area, flatness, surface, interface material and thickness, fastener pattern and torque. Air systems also need inlet temperature, altitude, flow, pressure and recirculation; liquid systems need fluid, inlet range, flow, pressure drop, compatibility, leak and condensation controls. Reject a design that passes only on an ideal cold plate or at room ambient.
Provide heat versus operating mode, allowable temperature rise, mechanical drawing, sensor location, environment and fault response. For example, 66 W through a 35°C baseplate-to-coolant budget allows at most 0.53°C/W for the assembled path. Verify that allocation at thermal equilibrium and during relevant transients with the delivered interface and cooling hardware.