The contact pressure on the interface material is generated by the heat sink attachment method. The typical attachment method for microprocessor heat sinks is spring clips, which produce approximately 5 to 15 psi (0.4 to 1.03 bar) of pressure.
High contact pressures would improve the thermal performance of interface materials since pressure will force air from the interface surface as well as force conformance of the interface material itself. In other words, high contact pressures can minimize the contact resistance of a system.
Unfortunately, many microprocessors are not durable enough to withstand high contact pressures. The thermal cost of applying a low contact pressure to a system will be dramatic if a highly conformable interface material is not selected. Thermal resistance values will rise under low contact pressure, since these values inherently reflect the contact resistance of the system
The graph to the right reflects the measured magnitude of this impact on several actual interface materials. Generally speaking, thermal resistance will typically be three times higher at low contact pressures than at high contact pressures (ie., 300 psi - 21 bar). | |  |