Igbt reliability

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 Copyright © 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


Assembling

Mounting torque

DCB crack

terminal broken

Mounting sequence

thermal grease distribution


Assembling

Applying thermal grease

thermal grease thickness high Rthch

thermal grease distribution DCB crack

TIM(thermal interface material)Screen printer


Assembling

ESD

IGBT is ESD sensitive component


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



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



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



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


IR- camera

¬ Temperature ripple detection is possible

¬ requires an open module

¬ Limited by high voltage



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


IR-SensorAssembly fixture

Customer made sample



Mechanical stress (vibration)

¬ Fixing block (force direction)

¬ Soft copper bus bar

¬ Fastness of capacitor


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


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


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


Calculate the losses and further more get temperature ripple.

losses Temperature ripple

Thermal model of system


Compare PC/TC curve with estimated number off temperature ripple


Cosmic radiation

DC link voltage

Altitude FIT



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



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


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



Over temperature

Hundreds of ms

Several s

Tens of s



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



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

Igbt reliability

Engineering

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