combined junction temperature and bond wire lift-off monitoring using auxiliary-emitter resistor

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Combined Junction Temperature and Bond-wire Lift-

off Monitoring Using Auxiliary-Emitter Resistor

Nick Baker

9th November 2016

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PhD Summary 2013-2016

Junction Temperature Measurement of IGBTs

- Junction Temperature is important for reliability

- Difficult to measure during converter operation

- PhD studied using the electrical behaviour of the semiconductor

as the ‘temperature sensor’

- No need for additional sensors inside the power module

Semiconductor Die An IGBT Module

Measure the temperature

of 1x1cm2 silicon

Powerex 2012

Integrated sensors take up

active area

In collaboration with

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Causes of Failure in Power Semiconductors

Temperature Swings and Coefficients of Thermal Expansion

- An IGBT module is constructed of many different materials

- Repetitive stress-strain from mismatches in CTE causes wearout

0

5

10

15

20

25

30

Copper Solder Silicon Aluminium DBC

CT

E (

pp

m/°

C)

Coefficients of Thermal Expansion (CTE)

Inside an IGBT module



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Temperature Sensitive Electrical Parameters (TSEPs)

- Main contribution of PhD Period:

- The ‘Peak Gate Current’ Method

- Peak Gate Current and Voltage Swing of Gate Driver are

measured to calculate the internal gate resistance Gate

CGCCGE

RGint


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Peak Gate Current Characteristics

- No load current compensation

- Linear temperature dependence

- No modification to gate driver structure or operation

- Accuracy depends on location of the internal gate resistor

- Being investigated by 2 companies


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IGBT

C

E

G

Bo

nd

-wire

+

-

Gat

e D

rive

r

RGint

ICIG

IGBT

C

E

G

Bo

nd

-wire

Aux. E

+-

Gat

e D

rive

r

RGint

ICIG

Kelvin-Emitter Gate Connection 1

Separate Paths for Gate Current and Collector Current

- Becoming more common with devices such as Silicon Carbide

(Infineon, ST, Wolfspeed have specific product lines for TO-247-4)

- Higher efficiency/Improved switching losses

‘Traditional’ ‘Kelvin-Emitter’

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Kelvin-Emitter Gate Connection 2

Paralleled Dies

- Gate Current and Load Current not completely decoupled

- Load current can travel through auxiliary bondwires

Infineon TO-247-4 Application Note

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Introduce Auxiliary Emitter Resistors

Paralleled Dies

- Gate resistance split between “RG” and Aux. Resistor

- Limits currents and oscillations

- Auxiliary Resistor should not be lower than 0.5Ω (Semikron,

Infineon)


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Introduce Auxiliary Emitter Resistors

Paralleled Dies

- Gate resistance split between “RG” and Aux. Resistor

- Limits currents and oscillations

- Auxiliary Resistor should not be lower than 0.5Ω (Semikron,

Infineon)


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Auxiliary Emitter Resistor Module Simulation

6x Paralleled SiC MOSFETs 50A (300A double pulse test)

- Step Resistances 1mΩ, 1Ω and 6Ω for each Aux. Source path

- Peak Currents through Aux. Source of MOSFET 1:

- 1mΩ: 30A

- 1Ω: <10A

- 6Ω: <5A

- Aux. Emitter/Source connection becoming more common

- Aux. Resistors may be used in modules with paralleled dies

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Bond-wire Lift-Off Detection 1

Most commonly studied failure mechanism

- Large amount of research on indicators to predict failure

- Usually device electrical behaviour is monitored

- Stop power module operation before catastrophic failure occurs

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Forward Voltage Drop used for Detection

- Established in lab, but how to prevent false positives in field?

- Small increase in Voltage before device failure (5%)

- Forward Voltage is influenced by:

- Packaging degradation, Gate Driver, VTH, Temperature..

40mV VCE

IGBT C

E

G

VV

Bond-wire

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100mV VCE

IGBT C

E

G

VV

Bond-wire

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60mV VCE

IGBT C

E

G

VV

Bond-wire

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Bondwire Lift-Off Detection with Aux. Emitter

Provides a specific measurement

- Only dependent on bondwire degradation (and temperature)

- Potential for increased sensitivity in both % and absolute terms if

an auxiliary resistor is included

VCE

IGBT C

E

G

VV

Bond-wire

IGBT C

E

G

VV

Bo

nd

-wire

Aux. E

VEE

Aux. Resistor

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Simulation with Aux. Emitter 1


- 50A die, 3 bond-wires each

- Resistances extracted using ANSYS

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- 50A die, 3 bond-wires each

- Resistances extracted using ANSYS

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Simulated Bondwire Lift-off, VEE @ 250A

- Simulated one die having 1,2, and all 3 bondwires removed

- With 1mΩ and 6Ω Aux. Resistor

71.9 74.3 76.6 81.2 75.4 82.2 95.2

576.3

0

100

200

300

400

500

600

700

Healthy 1 Bond Lift-

off

2 Bonds

Lift-off

All 3 Bonds

Lift-off

VE

E (

mV

)

Health State

1mΩ Aux. Resistor 6Ω Aux. Resistor IGBT C

E

G

VV

Bo

nd

-wire

Aux. E

VEE

Aux. Resistor

500mV

500%

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Circuit for Monitoring during Operation

More simple measurement circuit

- VCE requires high component count and protection against high

voltage in the off-state

- VEE is a low voltage signal (perhaps some spikes during switching)

- Possible to measure with just an instrumentation amplifier

IGBT C

E

G

Bo

nd

-wire

Aux. E

VEE

Aux. Resistor

Instrumentation Amplifier

VCE Measurement Concept (Bęczkowski 2013)

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Circuit for Monitoring during Operation

More simple measurement circuit

- VCE requires high component count and protection against high

voltage in the off-state

- VEE is a low voltage signal (perhaps some spikes during switching)

- Possible to measure with just an instrumentation amplifier

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Temperature Measurement using Aux. Resistor 1

Auxiliary Resistor could be located on the die

- Resistor now also acts as a temperature sensor

Gate

Aux. Emitter

Emitter

100mA-

500mACurrent

Source V

Aux. Resistor

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Temperature Measurement using Aux. Resistor 2

Auxiliary Resistor could be located on the die

- Polysilicon lumped resistor – similar to internal gate resistor

- Back contact resistors on die surface (e.g. IGBR from Vishay)

- Resistor should be a known temperature dependence, e.g.

1000ppm/°C

Back-contact resistor - Vishay

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Combined Bond-wire and Temperature Monitoring

VEE Monitored during both ON and OFF-state

- Bond-wires monitored during ON-state

- Temperature monitored during OFF-state

- Same voltage measurement can be used for both

250mA during OFF-State for temperature

IGBT

C

E

G

Bo

nd

-wire

Aux. E

+-

Gat

e D

rive

r

RGint


Aux. Resistor

VEE monitored while collector

current conducts for bond-wire monitoring

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Combined Bond-wire and Temperature Monitoring

VEE Monitored during both ON and OFF-state

- 250mA current injection for 20-30µs during OFF-state

- 1Ω total Aux. Resistor

- ~20x instrumentation amplifier gain: 5mV/°C sensitivity

250mA during OFF-State for temperature

IGBT

C

E

G

Bo

nd

-wire

Aux. E

+

-

Gat

e D

rive

r

RGint


Aux. Resistor

Temperature measurement voltage

during off-state Bond-wires monitored during on-state

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Summary

A Power Module with Auxiliary Emitter/Source Resistor

- Improves current sharing

- Provides opportunity to specifically monitor bond-wire lift-off,

with higher sensititvity

- Provides opportunity to implement junction temperature

monitoring

- Patent application for Tj measurement using the auxiliary emitter

resistor

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www.corpe.et.aau.dk

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combined junction temperature and bond wire lift-off monitoring using auxiliary-emitter resistor

Engineering