How to judge IGBT defects and failure
The device has IGBT failure due to internal chip failure, and it is difficult to detect and protect. Most of them can only be protected on the external characteristics of the system, and the body will still be greatly damaged. The high-voltage high-power IGBT module is composed of multiple chips and a large number of bonding wires. A large part of the functional failure of the device is caused by the aluminum bonding wire falling off or breaking. Early detection or identification of changes in electrical characteristics caused by such defects or failures is the leading criterion for constructing IGBT failures, which helps to avoid potential failure risks and improve IGBT utilization reliability.
Researchers Huang Jintian, Ling Chao, Sun Hu, and You Xiaojie of the School of Electrical Engineering, Beijing Jiaotong University, wrote in the Supplement 2 of the Journal of Electrical Engineering in 2019, and proposed to establish an equivalent circuit model of the parasitic parameters of the gate-source return path, and observe the internal The leading criterion for the influence of changes in spurious parameters on external operating characteristics. The criterion is based on the least squares parameter identification method, and the defects and failures of the internal chip and the bonding wire of the 6.5kV multi-core parallel IGBT module are determined in advance.
Insulated Gate Bipolar Transistor (IGBT) is a compound fully-controlled voltage-driven power semiconductor device composed of bipolar junction transistor (BJT) and insulated gate field effect transistor (MOSFET). There are two advantages of high input impedance of MOSFET and low on-voltage drop of power transistor (Giant Transistor, GTR).
Multiple IGBT and diode chips are packaged inside the IGBT module, and the chips are connected by bonding wires and converged to the module terminals. In practical applications, the performance difference of the chip will gradually accumulate and amplify and eventually lead to abnormal characteristics such as flow, voltage resistance, and heat transfer. The external manifestation is the degradation or failure of the device functionality. The premise of safe and reliable operation of IGBT modules is prevention, detection and implementation of protective measures.
Because IGBT modules, especially high-voltage and high-power modules, have poor working conditions, complex operating parameters, and variable system stray parameters, IGBT defect diagnosis encounters great obstacles, and it is not easy to put measurement devices inside the module, real-time monitoring of stray parameters is almost impossible achieve. The failure of IGBT mainly includes over-voltage failure, over-current failure, power or temperature cycle failure.
The main causes of overvoltage failure are VCE overvoltage, gate overvoltage, surge voltage, and static electricity; overcurrent failure is mainly related to short circuit, poor heat dissipation, and sudden change of switching frequency; power or temperature cycling failure is mainly temperature change Caused faster.
These failures are widespread in IGBT applications, the overall failure performance of the device is more obvious, but the internal chip partial failures or defects are difficult to observe.
Since the manufacturing process and packaging of high-power IGBT modules have very high technical requirements, the internal characteristics of the modules are the core technology of the manufacturers, and no more details will be announced. From the protection scheme of the chip and the bonding wire inside the module, the manufacturer has not provided it. In addition, the application conditions of high-power IGBTs are complex, and the operating characteristics reflect greater diversity. Device manufacturers and system suppliers generally only provide protection measures that are usually applied at the system level. .
Researchers from the School of Electrical Engineering, Beijing Jiaotong University have proposed a pilot criterion for device-level protection of the IGBT module body. By identifying the parasitic parameters of the internal chip and wiring of the module, the external characteristics caused by the changes of the stray parameters are found Changes to detect defects and failure risks of IGBT early. The grid-source channel reflow mathematical model of the internal stray parameters of the multi-chip parallel package IGBT module is constructed. The influence of the bonding wire parameters, chip layout, gate-source capacitance and gate resistance on the leading criterion is analyzed. The multiplication identifies the above-mentioned stray parameters to accurately reflect the changing characteristics of the internal parameters through the external characteristics, and finally realizes the early determination of internal defects and failures of the IGBT module.
Through simulations and experiments, the researchers compared the distribution of spurious parameters under different faults, and verified the effectiveness of the method in judging the internal fault type and fault degree of Infineon high-voltage high-power IGBT.
When the chip fails, the input capacitance parameter decreases, and the gate resistance and stray inductance parameters increase. When the gate resistance and stray inductance parameters increase by more than 10% and the input capacitance parameters decrease by more than 10%, it means that most of the internal bonding wires have fallen off or broken, or it may be the IGBT cell chip itself failure, system failure occurs at any time, the device It should be repaired or replaced immediately. When the gate resistance and stray inductance parameters increase by less than 10%, and the input capacitance parameter does not change much (not more than 2%), it indicates that a small amount of aluminum bonding wire failure may have occurred. The system has a risk of failure and the device body should Downgrade operation or maintenance.