1. IGBT reliability in converter design
Zhou Yizheng

2. How to destroy an IGBT module ?
Thermal stress
thermal cycling
power cycling
Mechanical stress
shock & vibration
forces on terminals
heat sink bending
Wrong handling
ESD
wrong mounting proc. by
Faulty control
shoot through(dead time)
short pulse
Voltage
VCE Over-voltage
VGE Over-voltage
Temperature
Tj >150°C
Tcase< -40°C
Other components
driver
bus bar
Current
IC short circuit
surge current
RBSOA / SOA

3. Converter reliability
Component qualification
Correct assembling
Proper design
Hardware
control
Lifetime & reliability estimation
Sufficient protection
Over voltage
Over current
Over temperature
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Assembling
Mounting torque
 DCB crack
 terminal broken
Mounting sequence
 thermal grease distribution
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Assembling
Applying thermal grease
 thermal grease thickness  high Rthch
 thermal grease distribution  DCB crack
TIM(thermal interface material)
Screen printer
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Assembling
ESD
IGBT is ESD sensitive component
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7. Proper design(hardware)
Vce overvoltage  must not exceed blocking voltage
Low commutation loop stray inductance
Proper Rgoff
Suitable protection in abnormal condition
Vge overvoltage  can not exceed 20V
 influence SC capability
Proper driving voltage level
Short gate cable length
Efficient clamping
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8. Proper design(hardware)
RBSOA
Maximum turn off two times of nominal current  over current protection point
SOA (Diode)
Peak power limitation
IGBT turn on speed
Stray inductance 1 2 3 !
1000
2000
3000
VR(t) [V]
IR(t) [A]
locus iR(t)*vR(t)
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9. Proper design(hardware)
Maximum junction temperature
Maximum operation temperature within limitation (including overload condition and temperature ripple)
 accurate losses calculation
Switching losses
 accurate thermal impedance value
Rthch
Rthha
 certain design margin
Considering aging issue
Considering lifetime
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10. Proper design(hardware)
Temperature sensing
Detect junction temperature
almost impossible for real products, but in lab…
1.Gate Resistor of IGBT chip as a sensor (RGINT)
2.Infrared Camera (IR-Camera)
3.Thermocouple
4.Infrared sensor
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11. Protection(temperature)
RGINT method
can detect chip junction temperature ripple
synchronization and sophisticated data acquisition are needed
measurements at high voltage are possible

12. Protection(temperature)
IR- camera
Temperature ripple detection is possible
requires an open module
Limited by high voltage
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13. Protection(temperature)
Thermocoupler
Special module need to be prepared
Not suitable for junction temperature ripple
Infrared sensor
Limited by high voltage
Customer made sample
IR-Sensor
Assembly fixture
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14. Proper design(hardware)
Mechanical stress (vibration)
Fixing block (force direction)
Soft copper bus bar
Fastness of capacitor
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15. Proper design(control)
Dead time (avoid short through)
driver delay may shrink dead time
Worst case is at small current condition
Software dead time VS. hardware dead time
Minimum pulse width
Short pulse will speed up switching
IGBT switching voltage spick
Didoe reverse recovery
Care about hardware dead time
tDT=[((tdoff(max)+tf(max))-tdon(min))+(tPHLmax-tPLHmin))]×1.5
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16. Proper design(Lifetime & reliability estimation)
Power cycling
Bonding wire reliability
Junction temperature ripple
Junction temperature
Cycling time
Thermal cycling
Soldering reliability
case temperature ripple
case temperature
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17. Proper design(Lifetime & reliability estimation)
Comparing to old generation chip, IGBT4 have around 4 times improvement with same max. junction temperature.
By improvement of bonding technology and chip metallization

18. Proper design(Lifetime & reliability estimation)
By improvement of material, soldering process, DCB shape…

19. How to estimate lifetime of IGBT module
What’s needed: Basic system parameters
Output current
Output frequency
Power factor
Modulation index
Switching frequency

20. How to estimate lifetime of IGBT module
Calculate the losses and further more get temperature ripple.
Temperature ripple
losses
Thermal model of system

21. How to estimate lifetime of IGBT module
Compare PC/TC curve with estimated number off temperature ripple

22. Proper design(Lifetime & reliability estimation)
Cosmic radiation
DC link voltage
Altitude
 FIT
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23. Proper design(Lifetime & reliability estimation)
High altitude effect
FIT rate(due to cosmic radiation)
Cooling
Clearance
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Protection (voltage)
DC link voltage overvoltage
 IGBT blocking voltage(active clamping voltage) limitation
 IGBT turn off snappy
Vce overvoltage
 more severer at overload and short circuit condition
 soft turn off, two level turn off
 active clamping
Vge overvoltage
 zener diode, TVS
 clamp to 15V
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Protection (current)
Over current
Two times of nominal current
Transient junction temperature within limitation
Short circuit
Short circuit time within 10us
Short circuit gate voltage limitation (SC energy, current)
Short circuit turn off after IGBT goes into desaturation
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26. Protection(temperature)
Over temperature
Hundreds of ms
Several s
Tens of s
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27. Protection(temperature)
Sensing case temperature
 time delay is around several seconds
 Require prior estimation delt Tjc max.
Sensing heatsink temperature
 time delay is around tens of seconds
 Require prior estimation delt Tjh max.
 suffer from Rthch changing due to thermal grease aging
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28. Protection(temperature)
Over temperature
How to realize fast and accurate temperature protection
Real time transient losses calculation, and
Temperature detection point(as close as to chip), and
Thermal impedance model
 Real time calculation of the junction temperature
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