IGBT failure cause analysis
The IGBT power module is a power module composed of insulated gate bipolar transistors (IGBT). Since the IGBT module is a MOSFET structure, the gate of the IGBT is electrically isolated from the emitter through an oxide film, which has excellent device performance. Widely used in servo motors, frequency converters, frequency conversion appliances and other fields.
There are several reasons for IGBT failure:
1. Overheating damage Instantaneous overheating caused by excessive collector current and other reasons, such as continuous overheating caused by poor heat dissipation, will damage the IGBT. If the device continues to be short-circuited, the power consumption generated by the large current will cause temperature rise. Due to the small heat capacity of the chip, its temperature will rise rapidly. If the chip temperature exceeds the intrinsic temperature of silicon (about 250°C), the device will lose its blocking ability, and the gate will The control cannot be protected, resulting in IGBT failure. In actual operation, the maximum allowable working temperature is generally about 130°C.
2. Exceeding the shut-off safe working area causes the latching effect and damages the latching effect. The latching effect is divided into static latching effect and dynamic latching effect. The IGBT is a PNPN4 layer structure. There is a parasitic thyristor in the body, and there is a body region expansion resistance Rs between the base and the emitter of the NPN transistor. The lateral hole current in the P-type body will generate a certain voltage drop on Rs. For the NPN base, Equivalent to a forward bias voltage. Within the specified collector current range, this forward bias voltage is not large enough to have any effect on NPN transistors. When the collector current increases to a certain level, the forward voltage is sufficient to turn on the NPN transistor, which in turn saturates the NPN and PNP transistors. As a result, the parasitic thyristor is turned on, and the gate loses control, forming a self-locking phenomenon, which is the so-called static latching effect. After the latching effect of the IGBT occurs, the collector current increases, resulting in excessive power consumption, resulting in device failure. The dynamic latching effect is mainly due to the fact that the current drops too fast when the device is turned off at high speed, and the dvCE/dt is large, causing a large displacement current, flowing through Rs, and generating a forward bias voltage sufficient to turn on the NPN transistor, causing the parasitic thyristor to self- Lock.
3. Transient overcurrent The large-scale overcurrent suffered by the IGBT during operation includes short-circuit, shoot-through and other faults, as well as the reverse recovery current of the freewheeling diode, the discharge current of the snubber capacitor, and the peak current caused by noise interference. Although this transient overcurrent lasts for a short time, if no measures are taken, it will increase the burden on the IGBT and may also cause the IGBT to fail.
4. Overvoltage causes collector-emitter breakdown.
5. Overvoltage causes gate-emitter breakdown.
6. If the IBGT glass passivation layer is damaged in the actual test, it is generally recommended that customers do component screening before mass production.