3.Thermocouple 4.Infrared sensor

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IGBT reliability in converter
design
Zhou Yizheng
How to destroy an IGBT module ?
Thermal stress
• thermal cycling
• power cycling
Wrong handling
Mechanical stress
• shock & vibration
• forces on terminals
• ESD
• heat sink bending
• wrong mounting proc.
by
Faulty control
Voltage
• shoot through(dead time)
• VCE Over-voltage
• short pulse
• VGE Over-voltage
Temperature
Other components
• Tj >150°C
• driver
• Tcase< -40°C
• bus bar
Current
•IC short circuit
• surge current
•RBSOA / SOA
Converter reliability
 Component qualification
 Correct assembling
 Proper design
 Hardware
 control
 Lifetime & reliability estimation
 Sufficient protection
 Over voltage
 Over current
 Over temperature
Set date
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Page 3
Assembling
 Mounting torque
 DCB crack
 terminal broken
 Mounting sequence
 thermal grease distribution
Set date
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Page 4
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
Set date
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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
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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
3
2000
2
1000
!
2000
IR(t) [A]
VR [500V/di v] IR [500A/di v]
3000
!
1
1000
0
0
locus iR(t)*vR(t)2
1000
0
Set date
2000
1
Copyright © Infineon Technologies
2010. All rights reserved.
tim e [400ns/div]
0
0
1000
2000 3 3000
Page 8
VR(t) [V]
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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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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Page 10
Protection(temperature)
 RGINT method
¬ can detect chip junction temperature ripple
¬ synchronization and sophisticated data acquisition are needed
¬ measurements at high voltage are possible
Ri
F1
S1
S2
F2
C
VRG
I0
RG
±V0
Gate bond
VGINT
RGINT= f(T)
G
E
IGBTChip
Protection(temperature)
 IR- camera
¬ Temperature ripple detection is possible
¬ requires an open module
¬ Limited by high voltage
Set date
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Page 12
Protection(temperature)
 Thermocoupler
¬ Special module need to be prepared
¬ Not suitable for junction temperature ripple
Customer made sample
Assembly
fixture
 Infrared sensor
IR-Sensor
¬ Not suitable for junction temperature ripple
¬ Limited by high voltage
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Page 13
Proper design(hardware)
 Mechanical stress (vibration)
¬ Fixing block (force direction)
¬ Soft copper bus bar
¬ Fastness of capacitor
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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
tDT=[((tdoff(max)+tf(max))-tdon(min))+(tPHLmax-tPLHmin))]×1.5
 Minimum pulse width
 Short pulse will speed up switching
¬ IGBT switching voltage spick
¬ Didoe reverse recovery
 Care about hardware dead time
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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
Set date
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Page 16
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
Proper design(Lifetime & reliability estimation)
By improvement of material, soldering process, DCB shape…
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
Proper design(Lifetime & reliability estimation)
 Cosmic radiation
 DC link voltage
 Altitude
Set date
 FIT
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Page 22
Proper design(Lifetime & reliability estimation)
 High altitude effect
 FIT rate(due to cosmic radiation)
 Cooling
 Clearance
1,E+07
1,E+06
RT, sea level
FF450R17ME4
Cosmic Radiation Induced Failure Rate
per Device
RT, 4000m
1,E+05
FIT
1,E+04
125°C, 4000m
1,E+03
1,E+02
1,E+01
1,E+00
1000
Set date
1050
1100
1150
1200
1250
1300
1350
1400
1450
1500
© Infineon Technologies 2010. All rights reserved.
VoltageCopyright
[V]
Page 23
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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Page 24
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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Page 25
Protection(temperature)
 Over temperature
Hundreds of ms
Several s
Tens of s
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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
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Page 27
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
Set date
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Page 28
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