Using a toothed spatula to ascertain the layer thickness of the thermal grease
after it has beenapplied to thebaseplate of the IGBTmodule
It has to be mentioned here that certain requirements regarding its surface finish are
placed on the heatsink. Hence a usual specification by IGBT module manufacturers is
that the heatsink should fulfil the following four requirements:
In the area where the module is mounted the surface roughness of the
heatsinkmust not exceed 10µm. However, a certainminimal roughness should
still exist (see further text below).
In the area where the module is mounted any surface warps of the heatsink
must not exceed 50µm.
The heatsink (as well as the module baseplate) must be free of damage and
The heatsink (as well as themodule baseplate) is to be cleaned with isopropyl
alcohol or ethanol beforeassembly, using a lint-free cloth.
Further, for the actual assembly of the module to the heatsink the manufacturer’s
directives are to be observed, regarding the minimum and maximum torque of the
mounting bolts as well as their tightening sequence
. Only in this way can an even
distribution of the thermal grease be assured on the one hand and a long-term
mechanical connection of both components on the other. Regarding this, manufacturers
publishapplication notes for theirmodules.
When thermal grease with high viscosity is used it may be necessary to pause after the first sequential
tightening step of the bolts, in order to give the paste sufficient time to spread evenly before themodule is fixed
with the final tightening torque.