IGBT reliability in converter design Zhou Yizheng.
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Transcript of IGBT reliability in converter design Zhou Yizheng.
IGBT reliability in converter designZhou Yizheng
Temperature
• Tj >150°C
• Tcase< -40°C
Current
•IC short circuit
• surge current
•RBSOA / SOA
Mechanical stress
• shock & vibration
• forces on terminals
• heat sink bending
Voltage
• VCE Over-voltage
• VGE Over-voltage
Faulty control
• shoot through(dead time)
• short pulse
Wrong handling
• ESD
• wrong mounting proc.
Thermal stress
• thermal cycling
• power cycling
by
How to destroy an IGBT module ?
Other components
• driver
• bus bar
Set date Page 3Copyright © Infineon Technologies 2010. All rights reserved.
Converter reliability
Component qualification
Correct assembling
Proper design
Hardware
control
Lifetime & reliability estimation
Sufficient protection
Over voltage
Over current
Over temperature
Set date Page 4Copyright © Infineon Technologies 2010. All rights reserved.
Assembling
Mounting torque
DCB crack
terminal broken
Mounting sequence
thermal grease distribution
Set date Page 5Copyright © Infineon Technologies 2010. All rights reserved.
Assembling
Applying thermal grease
thermal grease thickness high Rthch
thermal grease distribution DCB crack
TIM(thermal interface material)Screen printer
Set date Page 6Copyright © Infineon Technologies 2010. All rights reserved.
Assembling
ESD
IGBT is ESD sensitive component
Set date Page 7Copyright © Infineon Technologies 2010. All rights reserved.
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
Set date Page 8Copyright © Infineon Technologies 2010. All rights reserved.
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
2000
1000
0
1000
2000
3000
time [400ns/div]
VR
[5
00
V/d
iv]
IR
[5
00
A/d
iv]
1
23
!
0
0 1000 2000 30000
1000
2000
VR(t) [V]
IR(t
) [A
]
locus iR(t)*vR(t)
1
2
3
!
0
Set date Page 9Copyright © Infineon Technologies 2010. All rights reserved.
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
Set date Page 10Copyright © Infineon Technologies 2010. All rights reserved.
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
Protection(temperature)
C
E
G
RGINT= f(T) RG
IGBT-Chip VGINT VRG
F2 S2 S1 F1
I0
Gate bond ±V0
Ri
RGINT method
¬ can detect chip junction temperature ripple
¬ synchronization and sophisticated data acquisition are needed
¬ measurements at high voltage are possible
Protection(temperature)
IR- camera
¬ Temperature ripple detection is possible
¬ requires an open module
¬ Limited by high voltage
Set date Copyright © Infineon Technologies 2010. All rights reserved. Page 12
Protection(temperature)
Thermocoupler
¬ Special module need to be prepared
¬ Not suitable for junction temperature ripple
Infrared sensor
¬ Not suitable for junction temperature ripple
¬ Limited by high voltage
Set date Copyright © Infineon Technologies 2010. All rights reserved. Page 13
IR-SensorAssembly fixture
Customer made sample
Set date Page 14Copyright © Infineon Technologies 2010. All rights reserved.
Proper design(hardware)
Mechanical stress (vibration)
¬ Fixing block (force direction)
¬ Soft copper bus bar
¬ Fastness of capacitor
Set date Page 15Copyright © Infineon Technologies 2010. All rights reserved.
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
Set date Page 16Copyright © Infineon Technologies 2010. All rights reserved.
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
¬ Cycling time
Comparing to old generation chip, IGBT4 have around 4 times improvement with same max. junction temperature.
By improvement of bonding technology and chip metallization
Proper design(Lifetime & reliability estimation)
By improvement of material, soldering process, DCB shape…
Proper design(Lifetime & reliability estimation)
How to estimate lifetime of IGBT module
What’s needed: Basic system parameters
¬ Output current
¬ Output frequency
¬ Power factor
¬ Modulation index
¬ Switching frequency
How to estimate lifetime of IGBT module
Calculate the losses and further more get temperature ripple.
losses Temperature ripple
Thermal model of system
How to estimate lifetime of IGBT module
Compare PC/TC curve with estimated number off temperature ripple
Set date Page 22Copyright © Infineon Technologies 2010. All rights reserved.
Cosmic radiation
DC link voltage
Altitude FIT
Proper design(Lifetime & reliability estimation)
Set date Page 23Copyright © Infineon Technologies 2010. All rights reserved.
High altitude effect
FIT rate(due to cosmic radiation)
Cooling
Clearance
1,E+00
1,E+01
1,E+02
1,E+03
1,E+04
1,E+05
1,E+06
1,E+07
1000 1050 1100 1150 1200 1250 1300 1350 1400 1450 1500
Voltage [V]
FIT
FF450R17ME4Cosmic Radiation Induced Failure Rateper Device
RT, sea level
RT, 4000m
125°C, 4000m
Proper design(Lifetime & reliability estimation)
Set date Page 24Copyright © Infineon Technologies 2010. All rights reserved.
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
Set date Page 25Copyright © Infineon Technologies 2010. All rights reserved.
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
Set date Page 26Copyright © Infineon Technologies 2010. All rights reserved.
Protection(temperature)
Over temperature
Hundreds of ms
Several s
Tens of s
Set date Page 27Copyright © Infineon Technologies 2010. All rights reserved.
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
Set date Page 28Copyright © Infineon Technologies 2010. All rights reserved.
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