Power semiconductor cold knowledge: IGBT short-circuit junction temperature and times

[Guide]The maximum operating junction temperature of Infineon’s IGBT module is generally 150 degrees in the switching state, while the maximum operating junction temperature of IGBT7 can reach 175 degrees in the case of short-term overload. So can IGBT modules live in such a comfort zone for the rest of their lives?

IGBT short circuit characteristics

The maximum operating junction temperature of Infineon’s IGBT module in the switching state is generally 150 degrees, while the maximum operating junction temperature of the IGBT7 under short-term overload conditions can reach 175 degrees. So can IGBT modules live in such a comfort zone for the rest of their lives?

No! The module must enter society within 2 years after its birth. At the moment of putting on the whole machine and stepping into the society, it is often necessary to go through the short-circuit test. If the IGBT’s confidence is insufficient or the system protection is not strong enough, it will die.

It is inevitable for IGBTs to be short-circuited during the ten or even decades of switching high-voltage and high-current careers. Unfortunately, it may be caused by system and external interference, or even human operation errors.

IGBTs are allowed to be short-circuited, and there is such confidence. The data sheet of EconoDUAL™3 FF600R12ME4 600A 1200V describes the short-circuit capability in this way. When the driving voltage does not exceed 15V, the typical value of the short-circuit current is 2400A, as long as it is successfully turned off within 10us. Short-circuit current, the device will not be damaged. Note that the starting temperature of the short-circuit calibration is 150 degrees, how high will the junction temperature during the short-circuit process go up?

Power semiconductor cold knowledge: IGBT short-circuit junction temperature and times

Cold Knowledge No. 1: Will the maximum operating junction temperature be exceeded when the diode surges?

In order to understand the temperature when the IGBT is short-circuited, let’s first study the surge current of the diode. Let’s read a section of “Power semiconductor Devices-Principles, Characteristics and Reliability” by Mr. Lutz. He explained the fast recovery diode surge The temperature inside the chip under current.

There is an interesting example in the book. This is a 1200V fast recovery diode with an area of ​​49mm², soldered on a 0.63mm² DCB, a surge current width of 7.5ms, and a peak power of 3060W. At this time, the n-active layer temperature is as high as 385 degrees. Below the destruction limit, (the surge current of FRD is 10-12 times the rated current), the semiconductor itself will not be irreversibly changed, but the temperature of the chip solder layer also reaches 186 degrees, which is already very borderline. May cause irreversible changes in the package, so the surge current capacity is suitable for abnormal overload events, not the normal working state of power semiconductors.

Power semiconductor cold knowledge: IGBT short-circuit junction temperature and times

Surge current and voltage waveform

Power semiconductor cold knowledge: IGBT short-circuit junction temperature and times

Simulated temperature (Si aktiv silicon active area)

Cold Knowledge No. 2: How much do you know about the temperature when the IGBT is short-circuited

In Infineon’s early article, I found the temperature simulation curve at the time of short-circuit, and compared the temperature of IGBT2 NPT and IGBT3 at the time of short-circuit. It can be seen that when the initial short-circuit temperature Tvj=175 degrees, the maximum temperature during short-circuit is between 360 degrees and 461 degrees. high.

Power semiconductor cold knowledge: IGBT short-circuit junction temperature and times

Power semiconductor cold knowledge: IGBT short-circuit junction temperature and times

So how is the temperature distributed?

The temperature distribution in the longitudinal direction of the chip, the 1200V IGBT is short-circuited at 400V, and the initial temperature is 26 degrees. At 4.5us, the emitter temperature on the back of the chip is 77 degrees and the collector side of the chip is 167 degrees. The heat is concentrated at one point, and the temperature of the current wire is as high as 367 degrees, but the highest point is a point below the surface.

Power semiconductor cold knowledge: IGBT short-circuit junction temperature and times

Cold Knowledge No. 3: Can IGBT be short-circuited 100 times?

The instantaneous short-circuit power consumption is very large, and the junction temperature will far exceed the allowable operating junction temperature, so how many short-circuits can be?

Story 1:

In 2003, Infineon wrote an article that gave valuable experimental data:

The experiment is based on 3600A 1200V TRENCHSTOP IGBT3, VGE=15V, the highest operating junction temperature for short-circuit test, the actual short-circuit waveform is shown in the figure, short-circuit pulse 10us, cycle 1/3Hz, under such short-circuit conditions, the highest transient power consumption is as high as 3MW!

There is no problem if the 4 modules are short-circuited 90,000 times.

Power semiconductor cold knowledge: IGBT short-circuit junction temperature and times

In the experiment of that year, 3600A 1700V modules with high current specifications were used in the industry

Power semiconductor cold knowledge: IGBT short-circuit junction temperature and times

Short-circuit waveform, short-circuit current is nearly ten thousand amperes

Power semiconductor cold knowledge: IGBT short-circuit junction temperature and times

The number of short circuits of 4 modules

Story 2:

Lutz stated in the monograph that the energy stored in a short circuit cannot exceed the critical energy Ec. Repeated and long-term test results for short-circuit events show that the number of repetitions can be as high as 10,000 times on the premise that the device is not damaged. For the 600V IGBT studied, the short-circuit failure is entirely due to heat. In addition, special attention should be paid to the fact that after a large number of short-circuit pulses, the leakage current and threshold voltage of the IGBT do not change when the critical energy Ec is lower. However, as the number of pulses increases, the forward voltage drop Vce increases, and the short-circuit current Isc decreases. The failure analysis showed that after about 10,000 cycles, the resistivity of the aluminum metallization layer increased, the metallization layer of the chip caused by aluminum reconstruction was severely degraded, and the bonding wire was also degraded.

Power semiconductor cold knowledge: IGBT short-circuit junction temperature and times

Aluminum reconstruction caused by 24600 short circuits

Must understand knowledge:

What does the data sheet say?

Example of IGBT single tube: The data manual of IKW25T120, 25A 1200V single tube stipulates that the number of short circuits is less than 1000, and the interval is greater than 1 second.

Power semiconductor cold knowledge: IGBT short-circuit junction temperature and times

in conclusion

Undoubtedly, IGBT short circuit is a dangerous working condition, which cannot be avoided in many applications. The instantaneous power and extreme high temperature caused by the short-circuit current need to be borne by chips and devices. For system design engineers, it is necessary to consider:

1. The short-circuit conditions are extremely complicated, not designed, but accidents

2. The device may be damaged in a short circuit. Choose a reliable device that can withstand the short-circuit current and has a stable process

3. The system is designed to do a good job of detection and protection

Reference

1. REPETITIVE SHORT CIRCUIT BEHAVIOUR OF TRENCH-/FIELD-STOP IGBTS

2.Experimental behavior of single chip IGBT and CoolMOS™ devices under repetitive short-circuit condition

3.Short Circuit Properties of Trench-/Field-Stop-IGBTs –Design Aspects for a Superior Robustness

4.Aluminium Modification as Indicator of Current Filaments in IGBTs under Repetitive Short-Circuit Operation

Source: Infineon Industrial Semiconductor, original: Chen Ziying

The Links:   EP3C5F256I7N NL128102AC29-17