Surface Roughness Surface roughness is the average of the deviations both above and below the mean value of the surface height. For minimum interface resistance e.g. with conventional elastomeric pads a finish in the range 50-60 microinches is satisfactory. A finer finish is costly to achieve. Most commercially available cast or extruded heat sinks require spotfacing when used in high power applications. Back to Glossary 7.
Thermal capacitance is thus important in transients.
The larger the thermal capacitance the less a given pulse of power will increase temperatures in the device. Back to Glossary 8. This is a bulk property of the material and is independent of interfacial resistance e.g. a block of copper would have a very high thermal conductivity but when placed against a heat source with a rough surface could provide a high thermal resistance to ambient. Thermal conductivity represents ability to conduct heat once it has entered the material. Back to Glossary 9.