reliability testing of power devices - power · pdf file— residential pv — solar...

Andras Vass-Varnai

Product manager

Reliability Testing ofPower Devices

October 16, 2014

© 2014 Mentor Graphics Corp. Company Confidential

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Overview

Short introduction to the industrial challenges in powerelectronics

Brief theoretical overview of power cycling testing andthermal transient testing

Experimental examples

Overview of the MicReD Industrial Power Tester 1500A


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Insulated Gate Bipolar Transistors (IGBT) /Power Electronics Applications

Motor drives— Commercial motor drives— Motor drives discrete— Motor drives modules— Motor drives IPM

UPS— UPS discrete— UPS modules

PhotoVoltaic inverters— Commercial PV— Residential PV— Solar farms

Electric Vehicles/Hybrids— PHEV/EV— Full HEV— Mild HEV— Micro HEV— EV/HEV charging stations

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Railway traction— Rail traction inverters— Rail auxiliary inverters

Wind turbines— Wind turbine >1MW— Residential/commercial

wind turbines

Industrial applications— Welding— Other industrial

Consumer applications— Induction heating— DSC–DSLR camera flash— Air conditioner— Washing machine— Microwave oven— Flat panel (LCD/PDP)— Lighting supplies— Other home appliances

Others— Other power supplies

(SMPS)— Automotive ignition— Marine propulsion— Medical applications— Defibrillators— Avionics converters— Heavy duty vehicles— Grid –T&D

Classification by Yole Développement


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IGBT Market Forecast by Segment

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$0B

$1B

$2B

$3B

$4B

$5B

$6B

$7B

2011 2012 2013-E 2014-E 2015-E 2016-E 2017-E 2018-E

Others

Consumer applications

Industrial applications

Wind turbines

Rail traction

EV/HEV (+chargers)

PV inverter

UPS

Motor drives

Source: Yole Developpement - IGBT Markets & Application Trends, 2013


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IGBT technology trend –Power densities are increasing

Siemens User Meeting, June 20145


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Focus on Power Electronics Module Reliability

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Examples:— Hybrid & electric vehicle (EV)— Railway traction applications –

30+ year expected lifetime— Reusable energy production,

e.g., wind turbines, solar

10’s of thousands to millions ofcycles required

Issue is thermally induceddegradations due to powercycling & heat— Wire bond degradation— Metallization layer mismatch— Solder fatigue— Die and substrate cracks


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300 Amp IGBT Module

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Failure


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Vulnerable areas of a typical power device

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The thermomechanical stress is the most significantwhere the temperature change and the contact areabetween the layers are high


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Solder joint between the base plate and the back-sidemetallization of the substrate


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Die attach – There was extensive research in this fieldtowards better materials and processes


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Bond wires - Small area but high temperature swing andCTE mismatch make it vulnerable


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Traditional Power Cycle Failure Testing

Traditional Process:— Run set number of power cycles— Take to lab and test for failure— Repeat power cycling/lab testing

cycle until failure— Take to lab and determine

reason for failure

Power Cycle IGBTModule

Lab Test IGBT forFailure

Determine Causeof Failure- Visual

- Sonic/Xray- Dissection

Issues:— Repetitive cycle/lab test process =

long times— No “real time” indication of failure

in progress – only post mortem— Failure cause requires lab analysis

– typically internal to package

Repeat Process

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MicReD Industrial Power Tester 1500AProcess

3 phase equipment(22kW)

UPS

Highcurrent

COLDPLATE

SAFETY BOX

Cold Plate

DUT

Power grid

T3SterMeasurement

PowerCycling

Three 500A Power Sources

Touch Screen &T3Ster Software

Structure Function

Setup &Control

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T3Ster-Generated Structure Functions

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The Structure Functionshows how heat is flowingthrough a package fromjunction to ambient

Reference (good device)Structure Function is saved

Changes in the StructureFunction curve duringpower cycling identify aspecific change in thepackage— Delamination— Cracks in substrate— …….


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4. Analyze

T3Ster Test Workflow

Vsense

Isense1. Findthe TSP y = -0.001484x + 2.725130

2.580V

2.600V

2.620V

2.640V

2.660V

2.680V

2.700V

00.0°C 20.0°C 40.0°C 60.0°C 80.0°C 100.0°C

OSRAM - Calibration

2. Calibrate

Ipower

t

1

P(t)

P(t)

3a. PowerStep

t

T(t)

T(t)

3b. Record


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K-factor Calibration as per JESD51-1

T = VF·K [oC/mV]

Range > 50 oC

Linearity should be checked


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Thermal transient measurementsusing T3Ster

Device parameters are used as a thermometer

The change of the forward voltage (TSP – temperaturesensitive parameter) should be carefully calibrated againstthe change of the temperature (see JEDEC JESD51-1 andMIL-STD-750D)

JEDEC JESD51-1 compliant test setup


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T3Ster: What does it do?

P

TRthJA

T

t

T2

T1

ΔT

P1

P2

t

P

ΔP Thermal transientresponse curve as

measured by T3Ster

final steady-state

log t time

T temperature rise

initial steady-state

Due to switching the power, temperature changes:

Switch the power on (or off) in steady state and wait for the other steady state tooccur.While waiting for reaching the other steady-state, measure (record) the realtransient continuously, as it takes place.


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Real-time measurement of the transient

T3Ster: What does it do?

Thermal transientresponse curve as

measured by T3Ster

final steady-state

log t time

T temperature rise

initial steady-state

Can start at 1μs!

Up to 65000 sample points

Very high signal-to-noise ratio

with high accuracy & data density

Due to switching the power, temperature changes:

Switch the power on (or off) in steady state and wait for the other steady state tooccur.While waiting for reaching the other steady-state, measure (record) the realtransient continuously, as it takes place.


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The clever part is the T3Ster-Master analysis software:— Response curve is processed

— Resulting graphs show– Thermal capacitances

of internal features ofthe package (die, slug, etc.)

– Thermal resistancesbetween these featuresplus spreading resistancein these materials

— These are theStructure Functions

– cumulative– differential

Capacitances

Resistances

Cumulative

Differential

T3Ster: How does it work?


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Structure Functions:The Key to Understanding Thermal Structure

Cumulative Structure Function

Thermal impedance measured isconverted into a one-dimensionalintegral thermal resistance, heatcapacity of the heat-spread path:

Base

Grease

Die attach

R

C

Chip

Cold-plate

Base

Chip

Die attachJunction

Grease

Simplified Thermal Model

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Experiment I. – Setup and parameters

Sample 0-3

Iload 25 A

P ~200 W

ΔT ~100 °C

Control Mode const. I

THeating 3 s

TCooling 10 s

P

T

t(s)3 13 16 26

Devices mounted on temperature controlledcold plate

Base plate temperature: 25oC

Targeted junction temperature: 125oC

Constant current regardless of the voltagechange

Transient test after every 200 power cycles

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Experiment I. – Results 1.

All devices failed after approx. 40,000 power cycles

Broken bond-wires and burnt areas on the chip surface observed

In fact all IGBTs ultimately failed due to the overheating and damageof the gate-oxide:

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Continuous degradation ofthe die-attach layer can beobserved after ~10,000 to15,000 cycles

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0

0.005

0.01

0.015

0.02

0.025

0.03

0.035

0.04

0.045

0 5000 10000 15000 20000 25000 30000

RT

H,D

A/R

TH

,JA

,0

Power cycles

Relative die attach resistance

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0

0.005

0.01

0.015

0.02

0.025

0.03

0.035

0.04

0.045

0 5000 10000 15000 20000 25000 30000

RT

H,D

A/R

TH

,JA

,0

Power cycles

Relative die attach resistance


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Various control strategies

Constant current— Degradation has immediate impact

on resulting temperature swing, nocompensation

— Most severe strategy

Constant current, change of the cold-plate’s HTC

— Changes the flow rate of the coolant liquid in sync with the cycles— Helps to create a temperature swing at the case to induce failures

in the base plate solder— For longer cycle times

Constant power, PV

— Constant Ton and Toff

— Power losses are held constant by controlling the driving current

Constant ΔTJ=Const— Driving current control

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Experiment II. – Setup and parameters

Devices mounted on temperature controlledcold plate

Base plate temperature: 25oC

Targeted junction temperature change : 105oC

Various control strategies*

Transient test after every 250 power cycles

Number of additional parameters monitored continuously: Icycle, P, Von, Vhot,Vcold, Thot, Tcold, ΔTJ, ΔTJ/P

IGBT1 IGBT2 IGBT3

Iload 68 A 64.4 A 65 A

P 240 W 233 W 246 W

ΔTJ 105 °C 105 °C 105 °C

*Control Mode const. I const. P const. ΔTJ

THeating 3 s

TCooling 17 s

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Experiment II. – Results 1.

Well controlled test parameters— Variance of the controlled parameter is less than 0.1% (0.1W, 0.1

oC)

Although number of investigated samples was too low to draw anyquantitative conclusions, a significant difference can be observed inthe cycles to failure for the devices: Cycles until total

failure of the deviceConstant heating

current (I)~45 000

Constant heatingpower (P)

~65 000

Constant junctiontemperature change (ΔTJ)

~70 000

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Experiment II. – Results 2.

No sign of degradation in the heat flow path – variation of Rth is below 0.5%

Steep sections can be seen in the forward voltage of the diode at high currentlevel - these steps are indicative of bond wire damage/breakage

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Introducing the Industry-Unique MicReDIndustrial Power Tester 1500A

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Introducing the Industry-Unique MicReDIndustrial Power Tester 1500A

Industrial implementation of Mentor’sindustry-unique MicReD T3Ster technology

Provides fully automated power testing /cycling

Simple touch-screen user interface

For MOSFET, IGBT and generic two-poledevices – up to 3 simultaneously

Records diagnostic information during test:— Current, voltage and die temperature sensing— “Structure Function” identifies changes /

failures in package structure

Supports package development, reliabilitytesting, and batch checking of incoming partsbefore production

Touch Screen Controls

Structure Function

Power Tester 1500A

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Industry-Unique MicReD Industrial PowerTester 1500A

A simple process:— Connect devices— Set up device and cycling project— Run power cycles— “Structure Function” shows failure in

progress— Process is complete

The MicReD Industrial Power Tester 1500A:— Leverages MicReD’s industry-proven T3Ster

technology– Laboratory-precision accuracy

— Shortens total testing time up to 10x— Unique Structure Function diagnoses

degradation and causes of failure in “real time”— Enables multiple sample testing— Touch-screen interface enables quick setup and

use by both specialists and productionpersonnel

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reliability testing of power devices - power · pdf file— residential pv — solar...

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