Lifting-Off of Al Bonding Wires in IGBT Modules Under Power Cycling: Failure Mechanism and Lifetime Model

Lifting-off of Al bonding wires is one common failure mode of insulated-gate bipolar transistor (IGBT) modules during long-time operation. In the present work, the failure mechanism of Al wires lifting-off was investigated and the major factors were discussed based on both experiments and finite element (FE) simulations. It indicates that lifting-off of Al-wires is mainly determined by the interfacial thermal stress at the bonding interface. Thermal expansion of Al-wires and thermal mismatch of Al-Si interfaces contribute to the interfacial thermal stress which is affected by the resistance heat of Al-wires and power loss of Si-chips. Accordingly, a new lifetime model for the Al wires lifting-off failure mode of IGBT modules is proposed and verified through power cycling tests. The conduction current Ic, the heating time tON, and the junction temperature swing ΔTjare three major factors for the fatigue life model of IGBTs under Al wires lifting-off failure mode.