Thermal Management Thermal Resistance

Thermal resistance measurements are the most effective means of evaluating interface materials, since these measurements inherently reflect the impact of contact resistance on the system’s thermal performance.

Thermal resistance is minimized when the interface between two surfaces meets the following conditions:
1. Interface contains high thermally
conductive fillers.
2. Interface completely conforms to all surface roughness on both surfaces.
3. Interface completely and exactly fills the gap between the two surfaces.

Thermal resistances measured under standard test methods (as described in the “Test Methods” section of this brochure) should take care to meet the following controlled “ideal” conditions:
1. Flat interface surfaces.
2. Uniform contact pressure.
3. Uniform heat flow over the test area.
4. All heat loss occurs through
interface material.

In order to accurately reflect the thermal resistance of an interface material in a given system, the test setup must carefully simulate the system operation. This must include a test setup that reflects the surface roughness, the surface concavity, the application pressure and the microprocessor power of the actual system. It is critical that thermal resistance values of different interface materials are measured at the same contact pressures. In fact, it is impossible to accurately compare interface materials that are evaluated under different test conditions. Furthermore, these thermal resistances should be evaluated over the entire contact surface area rather than normalizing the thermal resistance to a one-square-inch area. Normalizing a thermal resistance value can give misleading results, since this calculation improperly assumes uniform heat flow over the test area.

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