The power handling capability of RF power resistors can be significantly increased by mounting the resistor on a copper plate to help drive the heat away from the resistive element. As figure A shows, as power is applied to the resistor, it is dissipated in the resistive film whose temperature increases until the thermal equilibrium is reached. Excess heat must be driven away from the resistive film to prevent damage. The excess heat is conducted first through the substrate which transfers it to the copper flange. The copper flange is mounted on a heatsink with a thermal interface material to optimize heat transfer, as shown in Figure C. Excessive film temperature is the principal cause of device failure. Maintaining the temperature at the bottom of the flange at or below the rated value will ensure that the film temperature is maintained at an acceptable value while applying maximum power.