Freeze baseplate or flange flatness, thermal-interface material, torque, orientation, heat sink, airflow direction and rate, or coolant inlet temperature and flow. State where temperature is sensed and how long the load must stabilize before pass/fail readings are taken.
Include ambient and case temperature, altitude or pressure, humidity, contamination, vibration and shock when they affect connectors, absorber material or cooling. Peak RF breakdown can change with pressure and geometry, so a sea-level room test may not represent a high-altitude pulse condition.
Acceptance should combine RF match, incident/reflected power and thermal evidence. Inspect for drift or damage and repeat critical S-parameters after the stress sequence; survival alone is insufficient when the load also serves as a calibration or protection boundary.