Extraction of parasitics within wire-bond IGBT modules

Parasitics are a major concern in design and layout of IGBT packages and power stages with both high switching speed and high power handling requirements. This paper presents the relationship between IGBT wire-bond package layout and its equivalent circuit parasitic inductance. It is shown that the dominant parasitic inductance inside the package mainly comes from the terminal leads. The parasitic inductance contributed by the wire-bonds is not a significant value. But the parasitic effects related to the closed coupling between the bonding wires causes several problems. They cause nonuniform current distribution between bonding wires, unbalanced transient current between paralleled IGBT chips in high power IGBT modules, as well as the mechanical stress on the connection joints induced by the magnetic fields. This phenomenon explains one of the wire-bonds' fatigue and failure mechanisms caused by the packaging parasitics. The analysis of packaging layout shows the possible options to reduce the parasitic inductance, alleviate the parasitic effects, and improve the module reliability.