IGBT reliability in converter design Zhou Yizheng

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

Converter reliability Component qualification Correct assembling Proper design Hardware control Lifetime & reliability estimation Sufficient protection Over voltage Over current Over temperature Set date Copyright © Infineon Technologies 2010. All rights reserved.

Copyright © Infineon Technologies 2010. All rights reserved. Assembling Mounting torque  DCB crack  terminal broken Mounting sequence  thermal grease distribution Set date Copyright © Infineon Technologies 2010. All rights reserved.

Copyright © 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 Copyright © Infineon Technologies 2010. All rights reserved.

Copyright © Infineon Technologies 2010. All rights reserved. Assembling ESD IGBT is ESD sensitive component Set date Copyright © 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 Copyright © 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 1 2 3 ! 1000 2000 3000 VR(t) [V] IR(t) [A] locus iR(t)*vR(t) Set date Copyright © 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 Copyright © 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 Set date Copyright © Infineon Technologies 2010. All rights reserved.

Protection(temperature) 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.

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 Set date Copyright © 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 Copyright © 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 Copyright © 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 Set date Copyright © Infineon Technologies 2010. All rights reserved.

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. Temperature ripple losses 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  FIT Set date Copyright © Infineon Technologies 2010. All rights reserved.

Proper design(Lifetime & reliability estimation) High altitude effect FIT rate(due to cosmic radiation) Cooling Clearance Set date Copyright © Infineon Technologies 2010. All rights reserved.

Copyright © 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 Copyright © Infineon Technologies 2010. All rights reserved.

Copyright © 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 Copyright © Infineon Technologies 2010. All rights reserved.

Protection(temperature) Over temperature Hundreds of ms Several s Tens of s Set date Copyright © 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 Copyright © 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 Set date Copyright © Infineon Technologies 2010. All rights reserved.