IGBT Modules - Technologies, Driver and Application (Second Edition) - page 372

control than a stencil with round holes, with regard to distribution and layer thickness of
the paste, so that inpractice this should be favoured.
The example shown here is an Infineon Technologies EconoDUAL
Even though other manufacturersmay offer a similar module case the template can not
be transferred to their module type. The reason for this is the internal positioning and
size of the DCB used. In the example shown in
it is clearly visible that three
DCB are used internally in themodule.
Fig. 10.4
Templatewith hexagonally punchedholes
If the option does not exist to use prefabricated templates the layer thickness of the
grease has to be checked manually once it has been applied by roller or spatula. For
this purpose a special teethed spatula is brought perpendicularly onto the grease once it
is applied and then drawn through the paste for a short run. This can reveal the layer
thickness which shows between the top part of the wetted teeth and the bottom part of
the non-wetted teeth. The concept is detailed in
Usually the layer thickness is
between 50µmand100µm.
Thermal grease is offered by various manufacturers. They are available with different
viscosities up to non-fluid. For assembly this means that pastes with low viscosity may
be applied relatively easily. Alas, these pastes have the tendency to separate into their
ingredients oil and filler when they are heated. This in turn has a negative effect on the
long term stability of the grease. The risk is that the transfer resistance R
will slowly
rise over time and then the power semiconductors are operated at an ever increasing
junction temperature due to the diminishing cooling. In the end thismeans a reductionof
reliability of the entire application. Thus, pastes with medium to high viscosity are
generally to be preferred. Not only but also because of this it is advisable to use
templates to apply the grease. For one this simplifies the assembly process and
furthermoremakes it reproducible and hencemore reliable.
is an InfineonTechnologies protected trademark.
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