IGBT Modules - Technologies, Driver and Application (Second Edition) - page 106

can apply sufficient pressure load (i.e. perpendicular to the contact point). This is the
only way to break down the initial oxidation layer by micro movements and enable the
contact to create a direct metallic connection. The required pressure load must remain
within the specifications for the entire lifetime of the system, otherwise the fretting
(not to be confused with the fritting effect) causes fretting corrosion, which
drastically increases the junction resistance.
Fig. 2.33
Exampleof spring contacts
2.4 Design concepts
2.4.1 Standard IGBTmodules
Standard IGBT modules are designed according to the process steps described in the
previous chapter. The latest developments are tending to replace traditional
construction techniques like soft soldering with more modern processes like diffusion
soldering and ultrasonic welding. In
examples of standard IGBTmodules are shown.
2.4.2 Presspack IGBTs
Press pack IGBTs have a similar design concept to the high-power diodes and
thyristors, which are offered as standard in ceramic packages. Their unique feature is
that the large upper and bottom sides of the press pack package are also the power
terminals and cooling surfaces of the component. This has the advantage of providing
cooling on both sides, but also the disadvantage that the heatsink design has to include
In a press pack package, it is essential that the assembly puts sufficient pressure on the
contact surfaces. This is the only way to make sure that there is good electrical and
mechanical contact internally between all the conducting elements (copper disk,
The fretting effect, a term from the field of tribology, describes the deterioration of contact points through
friction and vibration. In fretting, oxide particles from the contact point are abraded and compressed and can then
form a solid, poorly conductive layer within the contact point. The effect depends on the material, the contact
pressure, the presenceof any lubricants or liquids, the amplitudeof the vibrations and the number of cycles.
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