2.4.5 Discrete IGBTs
Modern IGBTs are usually offered with blocking voltages of up 1.2kV in a TO247
package. Occasionally, discrete IGBTs have voltages of up to 1.7kV, but they aremore
typically used in voltage classes of 600V and 1.2kV for the lowest power range. The
design of a discrete IGBT is best explained by lookingat an individual chip.
Design of a discrete IGBT
It begins with the lead frame, which comprises a copper alloy, fully or partially coated
with a layer of nickel phosphide (NiP). The lead frame is manufactured by punch-out.
The IGBT is usually soldered to the lead frame using a lead-free silver solder. Next in
line is the bonding process. The gate is bondedwith a finewire, the emitter with a heavy
wire. The collector, on the other hand, is connected electrically to the lead frame in a
soldering process. Until this point, all the connections are shorted to the lead frame. Not
until the lead frame has received its moulded package with the soldered and bonded
IGBT chip are the individual lead frames separated by a punch-out process, which also
takes out the electrical connectionof the gate, the emitter and the collector.
The compoundmaterial of the discrete IGBT is injectionmoulded around the lead frame
at high temperature (>150°C) and high pressure (>50Bar). After a dwell time of a few
seconds, the moulded components are hardened for several hours at high
temperatures, before finally being separated.
Electrical connectionby soldering and bonding processes ina discrete IGBT
Stacks, in the usual sense of the word, are not really an IGBT design variant. However,
as they are offered by some manufacturers of IGBTmodules, their design concept will
be briefly describehere.
A stack is generally a designwhich, in addition to IGBTmodules, contains adriver stage
and, if applicable, sensors to determine voltages (e.g. DC-bus voltage), currents (e.g.
phase currents) and temperatures (e.g. module temperature), aswell as a heatsink and,
where relevant, a DC-bus. Stacks are now offered for voltage classes of 600V to about