characterization of materials and their interfaces in a dbc substrate for power ... · 2018. 12....

Characterization of Materials and theirInterfaces in a DBC Substrate for Power

Electronics ApplicationsECPE Workshop “Future of Simulation”

Aymen BEN KABAAR1, Cyril BUTTAY2, Olivier DEZELLUS3,Rafaël ESTEVEZ1, Anthony GRAVOUIL4,

Laurent GREMILLARD5

1SIMaP, UMR 5266, CNRS, Grenoble-INP, UJF, France2 Univ Lyon, INSA-Lyon, CNRS, Laboratoire Ampère UMR 5005, F-69621, Lyon

3Univ Lyon, Univ Lyon 1, CNRS, LMI, UMR 5615, F-69622, Lyon4 Univ Lyon, INSA-Lyon, CNRS, LaMCoS, UMR 5259, F-69621, Lyon

5 Univ Lyon, INSA-Lyon, CNRS, MATEIS Laboratory, UMR 5510, F-69621, Lyon

21/11/18

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Outline

Introduction

Characterization of the copper layers

Characterization of the Ceramic Layer

Characterization of the Metal-Ceramic Interface

Conclusion

2 / 29

Outline

Introduction




Conclusion

3 / 29

Introduction – Power Electronic Module

Ceramic substrate EnsuresI Electrical insulationI Heat conduction

Direct Bonded CopperI Ceramic:

I Heat conductionI Electrical insulation

I Patterned Metal:I Forms circuitI Bonding to module

4 / 29

Introduction – Manufacturing of a DBC substrate

Copper

Ceramic

Copper

Ceramic

O2CopperOxide

Copper

Ceramic

EutecticMelt

Heating

O2 Diffusionand

Cooling

Copper

Ceramic

1080 -

1070 -

1060 -

1050 -

O2

0 0.4 0.8 1.2 1.6

Eutectic

Concentration in Atom%

Source: J. Schulz-Harder, Curamic [1]

I Standard: Al2O3/Cu (AlN also possible, with separate oxidation)I Bonding temperature very close to Cu melting point

Objective: modelling of the DBC for thermo-mechanical simulations

5 / 29

Introduction – Manufacturing of a DBC substrate

Copper

Ceramic

Copper

Ceramic

O2CopperOxide

Copper

Ceramic

EutecticMelt

Heating

O2 Diffusionand

Cooling

Copper

Ceramic

1080 -

1070 -

1060 -

1050 -

O2

0 0.4 0.8 1.2 1.6

Eutectic

Concentration in Atom%

Source: J. Schulz-Harder, Curamic [1]

I Standard: Al2O3/Cu (AlN also possible, with separate oxidation)I Bonding temperature very close to Cu melting point

Objective: modelling of the DBC for thermo-mechanical simulations5 / 29

Outline

Introduction




Conclusion

6 / 29

Copper – Preparation of the samples

Note: the content of this presentation is detailed in [2] and [3]

Tests on 3 Copper states:Cu3: Cu sheet prior to any processCu2: The same after DBC annealing (but

not bonded to ceramic)I temperature historyI no external mechanical stress

Cu1: Full DBC process, followed byetching of the ceramicI temp. and mech. history

Preparation and test:I Copper sheets supplied by CuramikI samples formed by electro-erosionI Uniaxial and cycling tensile tests

7 / 29

Copper – Tensile test

0.00 0.05 0.10 0.15 0.20 0.25 0.30Log(strain)

0

50

100

150

200

250

300

350

Cauc

hy S

tress

[MPa

]

Cu3 (no annealing)Cu2 (annealing, free cooling)Cu1 (Full DBC process)

I Dramatic change caused by annealing (yield stress)I Also, effect of mechanical stress on yieldÜ Further characterization on Cu1, more representative

8 / 29

Copper – Cycling test

0.00 0.01 0.02 0.03 0.04 0.05Log(strain)

0

20

40

60

80

100

120

Cauc

hy S

tress

[MPa

]

0.051 0.052 0.0530255075

100

I Tests on Cu1, repetitive stress 0–120 MPaI No compressive stress to prevent sample from buckling

I Ratchet effect caused by kinematic hardening of copperÜ Need for a suitable model (Armstrong-Fredericks [4])

9 / 29

Copper – Modelling

E ν σy C γ

127 GPa 0.33 60 MPa 1.7 GPa 14.6

0.00 0.01 0.02 0.03 0.04 0.05Log(strain)

0

20

40

60

80

100

120

Cauc

hy S

tress

[MPa

]

ExperimentModel

0.051 0.052 0.0530255075

100

I Satisfying modelling ofI ElasticI PlasticI Hardening

BehavioursI Parameters identification:

I E , ν, σy : uniaxial testsI C and γ: cycling tests

10 / 29

Outline

Introduction




Conclusion

11 / 29

Ceramic – Preparation of the samples

I 2 grades of Al2O3 tested:I standard, thickness=635 µmI “HPS” (Zr-reinforced),

thickness=250 µmI Material supplied by CuramikI Samples cut using a wafer sawI Sample size: 4 mm×40 mmI 3-point bending test.

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Ceramic – Bending Tests

0 5 10 15 20 25 30Specimen #

300

320

340

360

380

400

420

440

Youn

g's M

odul

us [G

Pa]

Al2O3Zr Al2O3 E =

FL3

48σwt3

I E : Young’s ModulusI F : maximum loadI w : sample widthI L: support spanI σ: deflectionI t : sample thickness

I good consistency in the resultsI few defects caused by the sample preparationI good quality of the base material

13 / 29

Ceramic – Bending Tests (2)

Weibull AnalysisI Considers the sample as a series of elementary volumesI Each volume has a statistical defect probability

I PSi : probability ofsurvival

I σw : Weibull stress

5.4 5.6 5.8 6.0 6.2 6.4 6.6log( W)

4

3

2

1

0

1

2

log(

log(

1/P s

i))

16.03x-92.59 R2=0.97

18.96x-121 R2=0.99

Al2O3Zr Al2O3

14 / 29

Ceramic – Modelling

Model usedI Purely elastic behaviorI Considers rupture

Identification of model parameters:I E : from bending testI ν: from literature [5]I m, σ0 and Veff : from Weibull analysis.

E ν m σ0 VeffAl2O3 403 GPa 0,22 16.03 322 MPa 0.103 mm3

Zr-Al2O3 330 GPa 0.22 18.95 590 MPa 0.501 mm3

15 / 29

Outline

Introduction




Conclusion

16 / 29

Interface – Test Principle

I DBC sample with a notch in top CuI 4-point bending testI Monitoring of fracture propagationI Parameter identification with FE

simulation

17 / 29

Interface – Preparation of the samples

I DBC configuration: 500 µm Cu / 250 µm Zr-Al2O3 / 500 µ CuI Chemical etching of copper patternsI Ceramic cutting with a wafer sawI Sample size: 10 × 80 mm2

18 / 29

Interface – Bending Tests

0 1 2 3 4Displacement [mm]

0.0

2.5

5.0

7.5

10.0

12.5

15.0

17.5

20.0Fo

rce

[N]

A

19 / 29



0.0

2.5

5.0

7.5

10.0

12.5

15.0

17.5

20.0Fo

rce

[N]

A

B

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0.0

2.5

5.0

7.5

10.0

12.5

15.0

17.5

20.0Fo

rce

[N]

A

B

C

19 / 29

Interface – Fracture Observation

Ceramic Copper

Cross section (SEM)

I Crack length measurementaccuracy: ±50µm

I Crack occurs at interfaceI No Al2O3 remaining on CuI ≈ 20µm bonding defectsÜ To be considered in

simulation

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Interface – Fracture Observation

Delaminated copper surface (SEM)

I Crack length measurementaccuracy: ±50µm

I Crack occurs at interfaceI No Al2O3 remaining on CuI ≈ 20µm bonding defectsÜ To be considered in

simulation

20 / 29

Interface – Cohesive model

Cohesive modelI Once TMax has been reached,

degradation occursI Gradual reduction in stiffnessI Eventualy, separation at interface

Implementation [6]I Simulation of the 4-point testI Cohesive zone between Al2O3 and

bottom CuI Two parameters: TMax and ΦSep

TMax

δ0 δcr δ

KΦSep

T

(1-D)K

[MPa]

[mm]

21 / 29

Interface – Cohesive model

Cohesive modelI Once TMax has been reached,

degradation occursI Gradual reduction in stiffnessI Eventualy, separation at interface

Implementation [6]I Simulation of the 4-point testI Cohesive zone between Al2O3 and

bottom CuI Two parameters: TMax and ΦSep

TMax

δ0 δcr δ

KΦSep

T

(1-D)K

[MPa]

[mm]

Copper

Copper

Ceramic

Cohesive zone

21 / 29

Interface – Model Identification

2 sources of data for model identification


0

2

4

6

8

10

Forc

e [N

]

0.0

0.2

0.4

0.6

0.8

1.0

crac

k le

ngth

[mm

]

0 1 2 3 405

1015 Force-Displacement

I “Macro” observationI focus on “peeling”

region

Crack lengthI “Local” observation

22 / 29




0

2

4

6

8

10

Forc

e [N

]

0.0

0.2

0.4

0.6

0.8

1.0

crac

k le

ngth

[mm

]

Force-DisplacementI “Macro” observationI focus on “peeling”

region

Crack lengthI “Local” observation

22 / 29




0

2

4

6

8

10

Forc

e [N

]

ForceCrack length

0.0

0.2

0.4

0.6

0.8

1.0

crac

k le

ngth

[mm

]

Force-DisplacementI “Macro” observationI focus on “peeling”

regionCrack lengthI “Local” observation

22 / 29

Interface – Model Identification (2)


4

6

8

10

12

Forc

e [N

]

Sep = 32 J/m2

no defect

MeasurementTmax=350 MPaTmax=300 MPaTmax=250 MPa

23 / 29



4

6

8

10

12

Forc

e [N

]

Sep = 32 J/m2

no defect


2.0 2.5 3.0 3.5 4.0Displacement [mm]

0.00

0.25

0.50

0.75

1.00

1.25

1.50

1.75

2.00

crac

k le

ngth

[mm

]

Sep = 32 J/m2

no defectMeasurementTmax=250 MPaTmax=300 MPaTmax=350 MPa

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4

6

8

10

12

Forc

e [N

]

Sep = 32 J/m2

no defect


2.0 2.5 3.0 3.5 4.0Displacement [mm]

0.00

0.25

0.50

0.75

1.00

1.25

1.50

1.75

2.00

crac

k le

ngth

[mm

]

Sep = 32 J/m2



4

6

8

10

12

Forc

e [N

]

Sep = 10 J/m2

20 µm defect

MeasurementTmax=350 MPaTmax=400 MPaTmax=450 MPaTmax=500 MPa

23 / 29



4

6

8

10

12

Forc

e [N

]

Sep = 32 J/m2

no defect


2.0 2.5 3.0 3.5 4.0Displacement [mm]

0.00

0.25

0.50

0.75

1.00

1.25

1.50

1.75

2.00

crac

k le

ngth

[mm

]

Sep = 32 J/m2



4

6

8

10

12

Forc

e [N

]

Sep = 10 J/m2

20 µm defect

MeasurementTmax=350 MPaTmax=400 MPaTmax=450 MPaTmax=500 MPa

2.0 2.5 3.0 3.5 4.0Displacement [mm]

0.00

0.25

0.50

0.75

1.00

1.25

1.50

1.75

2.00

crac

k le

ngth

[mm

]

Sep = 10 J/m2

20 µm defectMeasurementTmax=350 MPaTmax=400 MPaTmax=450 MPaTmax=500 MPa

23 / 29


200

250

300

350

400

T Max

[MPa

]

No defect

10 20 30Separation energy Sep [J/m2]

300

350

400

450

500

T Max

[MPa

]

With 20 m defect

Fits force/displacement measurementFits optical measurement

I Simulation for various:I ΦSep (separation energy)I TMax (crack initiation stress)I With or without defects

I A suitable parameter set fitsI “Macro” measurements

(Force/Displacement)I “Micro” measurements

(Crack length)

24 / 29

Outline

Introduction




Conclusion

25 / 29

Example of simulation resultsDelaminated area after 100 cycles (-50/+250°C)

0 1 2 3 4tcu/tcera

0.00

0.02

0.04

0.06

0.08

0.10

0.12Fr

actu

red

surfa

ce [m

m²]

Cu thickness=500 µmCu thickness=500 µm, with dimples

I Simulation predicts a strong effect of dimplesI Weakest configuration expected to be tCu = tCera

Ü Results compatible with existing data, especially for tCu >> tCera26 / 29

Simulation of the behaviour of a DBC structure

I We identified models forI Copper: behaviour very specific because of bonding processI Ceramic: must take into account material gradesI Interface: innovative approach with identifications at macro and

micro scalesI Theses models have been used for

I Evaluation of impact of stress-relaxation effectsI Identification of robust Cu/Al2O3/Cu configurationsI Evaluation of robustness to thermal cycling

Ü These simulations must be validated against measurements

27 / 29

Bibliography I

J. Schulz-Harder, “Ceramic substrates and micro channel cooler,” in ECPESeminar: High Temperature Electronics and Thermal Management, (Nürnberg),nov 2006.

A. Ben Kabaar, C. Buttay, O. Dezellus, R. Estevez, A. Gravouil, and L. Gremillard,“Characterization of materials and their interfaces in a direct bonded coppersubstrate for power electronics applications,” Microelectronics Reliability, 2017.

A. Ben Kaabar, Durabilité des assemblages métal céramique employés enélectronique de puissance.PhD thesis, 2015.

J. Lemaitre, J.-L. Chaboche, and J. Lemaitre, Mechanics of Solid Materials.CAMBRIDGE UNIV PR, 2002.

T. J. Ahrens, Mineral physics and crystallography: a handbook of physicalconstants.American Geophysical Union, 1995.

P. P. Camanho and C. G. Dávila, “Mixed-mode decohesion finite elements for thesimulation of delamination in composite materials,” tech. rep., NASA, 2002.

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Thank you for your attention.

This work was supported through the grant SuMeCe (Institut Carnot I@L, Lyon).

[email protected]

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characterization of materials and their interfaces in a dbc substrate for power ... · 2018. 12....

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