IGBT Modules - Technologies, Driver and Application (Second Edition) - page 516

14.5 Measures to improve the load cycle capability
Due to the inevitable losses and the interaction of different materials - and hence, the
different thermal resistances in power electronic devices - a temperature dropwill occur
from the point of generation to dissipation, which is the enclosure or a heatsink.
hows the temperature distribution, using the example of an IGBT module for a
given operating point, resulting from the different thermal resistances R
. The
temperature steps do not occur abruptly, but continuously across the different layers of
material. Not shown in detail here, is the temperature distribution over the chip solder,
the DCB, and the system solder, which in turn have different thermal resistance values
Fig. 14.14
Exampleof the temperature distribution for an IGBTmodule inoperation
In a real application, the operating points are not usually static but change dynamically
depending on the load profile. This results in varying temperature distributions, which,
due to the different CTE values of the materials, leads to the aging of the connections
between the layers of material. A lifetime of 10 years is generally estimated for standard
industrial applications, as already described in the section on the TC test. Other
applications may require an equal lifetime, but have a load profile that leads to faster
aging. Or the life span has to be significantly above 10 years with a similar load profile
as in the standard industrial application. Special modules have to be developed for
those applications to satisfy the demands. The following lists some activities that
contribute toan improvement of the load cycle capability inorder toachieve this goal.
14.5.1Matching theCTE values
As described in chapte
it is a general goal in the development of IGBTmodules,
to keep the differences between the CTE values of material combinations as low as
possible. For traction and wind power applications with their high demand on the load
cycle capability, therefore, AlSiC is used as the baseplatematerial andAlN for theDCB,
in order to ensure a lifetime of 15 to 30 years. This measure is to reduce the
delamination of the system solder.
The delamination of the system solder, i.e. the solder joint between the baseplate and
the DCB, always starts from the corners of the DCB
. By avoiding 90° angles
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