IGBT Modules - Technologies, Driver and Application (Second Edition) - page 374

Fig. 10.6
Influence of the surface roughness (finish)
Aside from the correct assembly of the module to the heatsink and the best possible
application of the thermal grease, the right choice of the paste in conjunction with the
heatsink and the module plays a major role. Both the heatsink surface and themodule
baseplate show a certain roughness. If this roughness is very low, for example because
the surfaces have been polished, a deterioration of the thermal transfer resistanceR
may result as detailed in
. In this case the particles of the thermal grease
cannot enter into the surface voids and act as spacers between module and heatsink
instead. Nometal-to-metal contacts can establish which are essential for a lowR
. If
instead a minimum roughness of the surfaces is assured (without falling into the other
extreme with very large voids) then metal-to-metal contacts can establish and a
correspondingly reducedR
Fig. 10.7
Influence of thegraining (particle size) of the thermal grease
Along these lines, the selection of the paste graining plays a role as shown i
schematically shows the influence of a compound with rough graining and
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