State Detection of Bond Wires in IGBT Modules Using Eddy Current Pulsed Thermography

Abstract

Insulated gate bipolar transistor (IGBT) modules are important safety critical components in electrical power systems. Bond wire lift-off, a plastic deformation between wire bond and adjacent layers of a device caused by repeated power/thermal cycles, is the most common failure mechanism in IGBT modules. For the early detection and characterisation of such failures, it is important to constantly detect or monitor the health state of IGBT modules， and the state of bond wires in particular. This paper introduces eddy current pulsed thermography (ECPT), a non-destructive evaluation (NDE) technique, for the state detection and characterisation of bond wire lift-off in IGBT modules. After the introduction of the experimental ECPT system, numerical simulation work is reported. The presented simulations are based on the 3-D electromagnetic-thermal coupling finite-element-method (FEM) and analyse transient temperature distribution within the bond wires. This paper illustrates the thermal patterns of bond wires using inductive heating with different wire statuses (lifted-off or well bonded) under two excitation conditions: non-uniform and uniform magnetic field excitations. Experimental results show that uniform excitation of healthy bonding wires, using a Helmholtz coil, provides the same eddy currents on each, whilst different eddy currents are seen on faulty wires. Both experimental and numerical results show that ECPT can be used for the detection and characterisation of bond wires in power semiconductors through the analysis of the transient heating patterns of the wires. The main impact of this work is that it is the first time electromagnetic induction thermography, so-called ECPT, has been employed on power/electronics devices. Because of its capability of contactless inspection of multiple wires in a single pass, and as such it opens a wide field of investigation in power/electronics devices for failure detection, performance characterisation and health monitoring.

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