A bond wire fracture is caused by repetitive, small movements of the bond wire. Over
the long term, this leads to fatigue and cracks appear in the bondwire. Themovements
are caused by the heating and cooling of the wire during operation. Movements by
magnetic fields arenegligible for this failuremechanism.
Lift-off of thebondwire from the chipmetallisation
Due to the constant heating and cooling of the chip surface during operation, the
structure of chip metallisation changes over time. Ultimately, the surface structure may
have changed so far that the bond wire connection to the chip surface is no longer
sufficiently strong. As a result, the bondwire separates from the chip surface.
PC curves for selected chip generations are published by the manufacturers of IGBT
modules to serve the user as a basis for the lifetime calculation .
example of this. The test conditions areas follows:
Maximum virtual junction temperatureT
Typical cycle time t
Heatingof themoduleby internal energisation