IGBT Modules - Technologies, Driver and Application (Second Edition) - page 371

Fig. 10.3
The use of templates to apply thermal grease
To reduce the thermal resistance R
it is therefore crucial to fill these warps or voids
with a substance which gives a better thermal resistance than the ambient air in the
voids. This is usually done with thermal grease (heat conductive paste). It needs to be
mentioned though that the use of thermal grease does reduce the R
-value compared
to that of air, however, it is still far from the low thermal resistance of the rest of the heat
path from semiconductor chip to ambient air. Thus it is beneficial to use only as much
thermal grease as is actually required. As an aid, somemanufacturers of IGBTmodules
offer templates with which just the right amount of thermal grease may be applied to a
particularmodule. For this themanufacturermeasures the roughness of themodule and
then calculates the necessary layer thickness and position of the paste on the
baseplate.When assembling with the aid of such a template, the paste only gets to the
area actually requiring it, and at the same time the areas with direct contact are
shows such a template with which the paste was applied to the
baseplate of the module
). A check after the assembly shows an even and
sparing distribution of the paste between themodule and the heatsink
in contrast, details the distribution of the paste when it has been applied with a
roller andwithout a template. Part of the paste has been squeezed out at the sides. But
still too much of it remained between the module and the heatsink so that the R
achieved is not the best.
In the template shown
round holes have been punched into it. Another type,
shown in
utilises hexagonal punch holes. This will result in a better process
The thermal grease should always and only be applied to the baseplate of the IGBT module. Never apply
directly onto the heatsink in order not to fill existing screw holes with grease and thus falsify the torque value of
the bolt assembly later.
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