The Insulated Gate Bipolar Transistor (IGBT) is a minority-carrier device with high input impedance and large bipolar current-carrying capability. Many designers view IGBT as a device with MOS input characteristics and bipolar output characteristic that is a voltage-controlled bipolar device. To make use of the advantages of both Power MOSFET and BJT, the IGBT has been introduced. It’s a functional integration of Power MOSFET and BJT devices in monolithic form.
Gideon Analytical Laboratories received two Printed Circuit Boards (PCBs) with failed Insulated-gate bipolar transistors (IGBTs). The IGBTs were Toshiba GT40T301s. An insulated-gate bipolar transistor is a three-terminal power semiconductor device primarily used as an electronic switch which, as it was developed, came to combine high efficiency and fast switching. It switches electric power in many modern appliances: variable-frequency drives (VFDs), electric cars, trains, variable speed refrigerators, lamp ballasts, air-conditioners and even stereo systems with switching amplifiers.
Gideon Analytical Laboratories performed failure analysis on severalIXYS IGBT IXGH32N60B transistors, encased in TO-247 packages. These transistors are 60 amp 600V 2.3 Rds 200W. The concern was that the devices were not functioning as 600V but topped out at 480V in the application.
Displayed in the picture above is a defect near the guard ring. Further analysis revealed there are several metal posts contacting more than likely underlying diffusion for voltage termination.