Application Pressure
The pressure required to attach an interface material to a heat sink or to a microprocessor. Application pressure is typically measured in pounds per square inch (psi).
Contact Pressure
The pressure between the microprocessor and the heat sink. This pressure is typically generated and maintained by the heat sink clips which attach to a socket. Contact pressure is typically measured in pounds per square inch (psi).
Contact Resistance
In thermal transfer, air equals resistance. Thus, contact resistance is a theoretical measure of the volume of air voids along the interface of any two surfaces. These microscopic voids are formed by surface roughness, surface concavity or the interface material ineffectively conforming to a component’s surface. This is illustrated in the magnified section of Diagram 2.
Dielectric Strength
A measure of the voltage required to cause a breakdown of a specific thickness of interface material. Dielectric strength is typically expressed in units of volts/mil.
Interface Gap
The gap which results between the microprocessor and the heat sink due to the stack-up of flatness specification tolerances. Two nominally flat surfaces will always produce an interface gap when placed together
Thermal Conductivity
The ability of a material to conduct heat after the heat has entered that material. Thermal conductivity values can be misleading when used to evaluate thermal interface materials since actual performance is affected by the contact resistance with both the heat sink and the microprocessor. Thermal conductivity is typically expressed in units of W/m-K.
Thermal Impedance
A defined parameter which is calculated by dividing the temperature difference across the interface by the power output of the microprocessor. Thermal impedance values are quite valuable in thermal management design since they inherently reflect the impact of contact resistances on interface performance. Low thermal resistances indicate a system which dissipates heat effectively. Thermal impedance is typically expressed in units of °C-in2/W.