IGBT Modules - Technologies, Driver and Application (Second Edition) - page 96

Once a conducting path has been created by this mechanism, the second mechanism
can begin, if necessary. This is based on the dilation of the conducting channel through
the flow of an electrical current and corresponding heating of the breakdown point. The
secondmechanism always results from the first and cannot occur on its own.
In the power and control terminals of IGBT modules, contamination of the contact
partners is not critical, as there is always sufficient voltage there and the currents are
usually high enough to clean the contact. This is not the case for signal inputs and
outputs for measuring temperature, current and/or voltage, with their smaller measuring
circuit voltages and currents. The fritting process does not completely and thoroughly
deal with the increase in contact resistance due to corrosionor contamination.
Fig. 2.22
Contact partnerswith additional external layer Screw connection
The best-known type of electrical connection is the screw connection. When properly
applied, this is very reliable and is the main connection technology for all IGBT high-
current and high-voltagemodules. For electric currents of 200A and blocking voltages of
1.2kV and higher, using IGBT components in printed circuit boards becomes a real
challenge, because of the current handling capacity of the electrical contact and the
conducting tracks on the PCB itself. A screw connection has the advantage of a
generously sized base and therefore low contact resistance. Inmost IGBTmodules, the
electrical contact
as described in chapter
is thermally bonded to the baseplate
via theDCB. This cools the contact andprevents thermal run-away under full load.
The contacts between the screw connection and the DCB in the modules are made of copper. The copper
parts are usually silver plated or given a nickel/tin coating, with layer thicknesses of up to 3µm for silver and up to
14µm for nickel/tinalloys.
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