IGBT Modules - Technologies, Driver and Application (Second Edition) - page 93

The bonding of two identical materials, in this case both copper, thus forms a closed
structure at the interfaces with a strong metallurgical bond, creating the greatest
possible conductivity. In addition, the identical materials have the same coefficient of
thermal expansion, which means that there is a significant reduction in the mechanical
stress at these joint locations under thermal load.
Fig. 2.19
Cross-section of anultrasonicallywelded joint inan IGBTmodule
The simulation results i
show a current of I
= 400A at a load terminal joined
with bond wires and amaximum temperature at the aluminium bond wires of 200°C. In
contrast, the simulation with the ultrasonically welded joint shows a maximum
temperature of 120°C. The results of these simulations therefore clearly show that
ultrasonic welding has a much greater current handling capacity than traditional
aluminiumbonded joints.
Fig. 2.20
Thermal comparison of an ultrasonicallywelded joint (copper to copper) with a
framebond joint (aluminium to copper)
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