IGBT Modules - Technologies, Driver and Application (Second Edition) - page 511

It is important that an examination of the leakage current immediately after the H3TRB
test does not make sense, as, due to the remaining moisture in the component,
measuring errors could occur. Therefore, the device under test is stored directly after
the test for aminimum of 2hand amaximumof 24hwith subsequent annealing of 24h.
The TST is carried out for a defined number of cycles, in a bicameral system. The unit
under test is brought to a low temperature (e.g. -40°C) in the one chamber and then in
the other chamber to a high temperature (e.g. 125°C). The time in each chamber (e.g.
1h) must be sufficiently long, so the test object will adopt a uniform temperature. The
change between the chambers must also take place within a defined time, typically
below30 seconds.
During the TST, themodule is not operated electrically. Criterion for test is the complete
system, which has to be checked mechanically, electrically and thermally. If during or
after the test a mechanical malfunction occurs (e.g. rupture of the housing) the test is
not passed. The same applies for the electrical and thermal properties (e.g. changes in
the thermal resistanceR
by +20%).
Focus of the test of the IGBT module is the housing and the interface between the
baseplate and theDCB (system solder).
In contrast to the TST, the TC test is conductedwith shorter cycle times, in the range of
a fewminutes (typically 5min). The heating of themodulemay be passive, i.e. through
an external heat source, or active, by energising the module. The decisive criterion for
the TC test is the thermal resistance R
. This is measured before the test as a
reference. If during or after the test, a change occurs outside a defined area (e.g.
+20%), the test is not passed.
Focus of the test of the IGBT module is the interface between chip and DCB (chip
solder) and betweenDCB andbaseplate (system solder).
Specifically for the two tests TC and TST, the correct choice of materials plays a crucial
role. In a conventional IGBT power module, a number of different materials are
combined into one system. Each of these materials behaves differently with respect to
its expansion when it is heated and cooled. This material property is expressed by the
so-called coefficient of thermal expansion (CTE) value.
The greater the difference inCTE of twomaterials combined, the greater the stress that
occurs at the connection point during heating and cooling. The aim therefore is to
combinematerials with aminimum difference inCTE value directly, in order to keep the
wear (delamination) at a minimum and to increase the lifetime. For this reason, for
example, tractionmodules use the followingmaterial combinations (chapter
Silicon –AlN ceramics –AlSiCbaseplate
Even with extreme temperature changes, this assures a cycle capability in the
application of up to 30 years. Due to cost reasons (AlSiC ismore expensive than copper
baseplates) as well as a typical product life of 10 years, the following combination of
materials has established itself for industrial applications:
Silicon –Al
ceramics – copper baseplate
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