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Assembly Instructions
AN2009-01
Applying the Thermal Grease
Application Note 17 V2.2, 2015-02
8 Applying the Thermal Grease
Due to the individual surface shape (e.g. roughness and flatness) of the heatsink and the module these
do not touch across the entire area so that a certain localized separation between the two components
cannot be avoided.
To dissipate the losses occurring in the module and to achieve a good flow of heat into the heatsink, all
localized cavities have to be filled with a thermal compound. When using a heat conductive paste, a
homogenous application needs to be assured.
A well applied layer will fill all cavities and at the same time does not prevent the metallic contact
between module base and heatsink surface. A compound should be selected which shows
permanently elastic features in order to assure a continuously favorable heat transfer resistance.
Before the module is mounted onto the heat sink an even layer of thermal grease, 80 µm thick, should
be applied to the module base or to the heat sink according to the module size and used thermal
grease. This grease can be applied using either a spatula, a roller or by a silk screen printing. The
quantity of thermal grease is sufficient if a small amount of grease is visible around the module after
assembling it to the heat sink.
Recommended is the application of thermal grease by means of a screen print process. Apart from an
optimized and module specific distribution of the heat conductive paste, a homogenous and
reproducible layer thickness is achievable with this procedure. If a screen print process is used the
layer thickness could be reduced to values under the above mentioned numbers. The size of the
module and the viscosity of the thermal grease are important factors in this case.
Further notes regarding the application of screen print templates for the application of thermal grease
can be found in the application note AN2006-02 Application of silk screen.