IGBT Modules - Technologies, Driver and Application (Second Edition) - page 84

operating conditions. Optimisation of the thermal transfer resistance in a cold, bolted
down state is of secondary importance.
2.2.4 Moulding compound, epoxy resin and siliconegels
Moulded compound is the material used to encapsulate discrete IGBTs and IGBT
modules with low currents and voltages. Moulded modules are most familiar to us in
applications with blocking voltages up to 600V and currents of less than 10A. However,
this technology is increasingly beingapplied in higher power and higher blocking voltage
areas. Moulded compound contains approximately 20-30% epoxy resin, quartz, a flame
retardant and a curing agent. Themoulded compound is worked under high pressure of
≥60bar and at a temperature of ≥170°C. This process is also called resin transfer
(RTM) and is familiar from some manufacturers' product descriptions:
Fig. 2.6
Modulewith epoxy layer andmouldmodules
In standard IGBT modules, it is – or was, for a time – usual to use epoxy resin as
insulating compound, because of its good dielectric properties. Like the package
plastics, an epoxy resin consists of polymers which, depending on the reaction that
occurs, produce a thermosetting plastic with a high degree of rigidity and chemical
stability, with the addition of suitable hardeners. Once the epoxy resin and hardener are
Resin transfer moulding is also known as "injectionmoulding", in which amoulding compound is injected into a
mould at high pressure and heat. During the dwell time in the closedmould, themoulding compoundeither reacts
or vulcanises. After hardening, themould tool can be opened inorder to remove themouldedpart.
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