Detection of aging related IGBT bond-wire lift-off using spread spectrum time domain reflectometry (SSTDR)

Degradation in Insulated Gate Bipolar Junction Transistor (IGBT) modules leads to reliability issues in high power applications. When thermal and electrical stress factors are subjected to large IGBT modules, natural degradation takes place, and cracks are formed on Si surface where bond wires are attached to the die. These cracks and lift-offs eventually degrade the device performance leading to a complete failure. A new technique is introduced in this paper to detect bond-wire lift-off incidents in large (i.e. 1200V, 900 A) IGBT modules using Spread Spectrum Time Domain Reflectometry (SSTDR). Most of the existing IGBT bond-wire lift-off detection methods are performed by separately aging the modules while isolating them from the rest of the system. In contrast, the proposed method can determine lift-off incidents while the IGBT is functional in a live power converter. Through experimental results, we were able to establish a pattern between number of detached bond wires and SSTDR correlated output, and the SSTDR results are independent of the IGBT operating points; thus making the SSTDR based method a very robust technique.