Characterization of Materials and their Interfaces in a DBC Substrate for Power Electronics Applications

Characterization of Materials and their

Interfaces in a DBC Substrate for Power

Electronics Applications

Aymen BENKABAAR1, Cyril BUTTAY2, Olivier DEZELLUS3,

Rafaël ESTEVEZ1, Anthony GRAVOUIL4, Laurent GREMILLARD5

1_{SIMaP, UMR 5266, CNRS, Grenoble-INP, UJF, France}

2_{Univ Lyon, INSA-Lyon, CNRS, Laboratoire Ampère UMR 5005, F-69621, Lyon} 3_{Univ Lyon, Univ Lyon 1, CNRS, LMI, UMR 5615, F-69622, Lyon} 4_{Univ Lyon, INSA-Lyon, CNRS, LaMCoS, UMR 5259, F-69621, Lyon} 5_{Univ Lyon, INSA-Lyon, CNRS, MATEIS Laboratory, UMR 5510, F-69621, Lyon}

Outline

Introduction

Characterization of the copper layers

Characterization of the Ceramic Layer

Characterization of the Metal-Ceramic Interface

Outline

Introduction

Characterization of the copper layers

Characterization of the Ceramic Layer

Characterization of the Metal-Ceramic Interface

Conclusion

Introduction – Power Electronic Module

Ceramic substrate Ensures

I Electrical insulation I Heat conduction

Direct Bonded Copper

I Ceramic:

I Heat conduction

I Electrical insulation

I Patterned Metal:

I Forms circuit

Introduction – Power Electronic Module

Ceramic substrate Ensures

I Electrical insulation I Heat conduction

Direct Bonded Copper

I Ceramic:

I Heat conduction

I Electrical insulation

I Patterned Metal:

I Forms circuit

Introduction – Manufacturing of a DBC substrate

Copper

Ceramic

Copper

Ceramic

O2 Copper_Oxide

Copper

Ceramic Eutectic Melt Heating

O2Diffusion

and 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

Introduction – Manufacturing of a DBC substrate

Copper

Ceramic

Copper

Ceramic

O2 Copper_Oxide

Copper

Ceramic Eutectic Melt Heating

O2Diffusion

and 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

Outline

Introduction

Characterization of the copper layers

Characterization of the Ceramic Layer

Characterization of the Metal-Ceramic Interface

Conclusion

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 process Cu2: The same after DBC annealing (but

not bonded to ceramic)

I temperature history

I no external mechanical stress

Cu1: Full DBC process, followed by etching of the ceramic

I temp. and mech. history

Preparation and test:

I Copper sheets supplied by Curamik I samples formed by electro-erosion I Uniaxial and cycling tensile tests

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 process Cu2: The same after DBC annealing (but

not bonded to ceramic)

I temperature history

I no external mechanical stress

Cu1: Full DBC process, followed by etching of the ceramic

I temp. and mech. history

Preparation and test:

I Copper sheets supplied by Curamik I samples formed by electro-erosion I Uniaxial and cycling tensile tests

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 process Cu2: The same after DBC annealing (but

not bonded to ceramic)

I temperature history

I no external mechanical stress

Cu1: Full DBC process, followed by etching of the ceramic

I temp. and mech. history

Preparation and test:

I Copper sheets supplied by Curamik I samples formed by electro-erosion I Uniaxial and cycling tensile tests

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 process Cu2: The same after DBC annealing (but

not bonded to ceramic)

I temperature history

I no external mechanical stress

Cu1: Full DBC process, followed by etching of the ceramic

I temp. and mech. history

Preparation and test:

I Copper sheets supplied by Curamik I samples formed by electro-erosion I Uniaxial and cycling tensile tests

Copper – Tensile test

0.00 0.05 0.10 0.15 0.20 0.25 0.30

Log(strain)

0

50

100

150

200

250

300

350

Cauchy Stress [MPa]

Cu2 (annealing, free cooling)

Cu1 (Full DBC process)

I Dramatic change caused by annealing (yield stress) I Also, effect of mechanical stress on yield

Copper – Cycling test

0.00 0.01 0.02 0.03 0.04 0.05

Log(strain)

0

20

40

60

80

100

120

Cauchy Stress [MPa]

0.051 0.052 0.053

0

25

50

75

100

I Tests on Cu1, repetitive stress 0–120 MPa

I No compressive stress to prevent sample from buckling

I Ratchet effect caused by kinematic hardening of copper

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 0.05

Log(strain)

0

20

40

60

80

100

120

Cauchy Stress [MPa]

Experiment Model

0.051 0.052 0.053

0

25

50

75

100

I Satisfying modelling of

I Elastic

I Plastic

I Hardening

Behaviours

I Parameters identification:

I E,ν,σy: uniaxial tests

Outline

Introduction

Characterization of the copper layers

Characterization of the Ceramic Layer

Characterization of the Metal-Ceramic Interface

Conclusion

Ceramic – Preparation of the samples

I 2 grades of Al2O3tested:

I standard, thickness=635µm

I “HPS” (Zr-reinforced), thickness=250µm

I Material supplied by Curamik I Samples cut using a wafer saw I Sample size: 4 mm×40 mm I 3-point bending test.

Ceramic – Bending Tests

0

5

10

15

20

25

30

Specimen #

300

320

340

360

380

400

420

440

Young's Modulus [GPa]

Al2O3

Zr Al2O3 E = FL

3

48σwt3

I E: Young’s Modulus I F: maximum load I w: sample width I L: support span I σ: deflection

I t: sample thickness

I good consistency in the results

I few defects caused by the sample preparation

Ceramic – Bending Tests (2)

Weibull Analysis

I Considers the sample as a series of elementary volumes I Each volume has a statistical defect probability

I P_Si: probability of survival

I σw: Weibull stress

5.4

5.6

5.8

6.0

6.2

6.4

6.6

log(

)

4

3

2

1

0

1

2

log

(lo

g(

1/

P

))

16.03x-92.59

R

_=0.97

18.96x-121

R

_=0.99

Ceramic – Modelling

Model used

I Purely elastic behavior I Considers rupture

Identification of model parameters:

I E: from bending test I ν: from literature [5]

I m,σ0andVeff: from Weibull analysis.

E ν m σ0 Veff

Al2O3 403 GPa 0,22 16.03 322 MPa 0.103 mm3 Zr-Al2O3 330 GPa 0.22 18.95 590 MPa 0.501 mm3

Outline

Introduction

Characterization of the copper layers

Characterization of the Ceramic Layer

Characterization of the Metal-Ceramic Interface

Interface – Test Principle

I DBC sample with a notch in top Cu I 4-point bending test

I Monitoring of fracture propagation I Parameter identification with FE

Interface – Preparation of the samples

I DBC configuration: 500µm Cu / 250µm Zr-Al2O3/ 500µCu I Chemical etching of copper patterns

I Ceramic cutting with a wafer saw I Sample size: 10×80 mm2

Interface – Bending Tests

0

1

2

3

4

Displacement [mm]

0.0

2.5

5.0

7.5

10.0

12.5

15.0

17.5

20.0

Force [N]

Interface – Bending Tests

0

1

2

3

4

Displacement [mm]

0.0

2.5

5.0

7.5

10.0

12.5

15.0

17.5

20.0

Force [N]

A

Interface – Bending Tests

0

1

2

3

4

Displacement [mm]

0.0

2.5

5.0

7.5

10.0

12.5

15.0

17.5

20.0

Force [N]

A

Interface – Bending Tests

0

1

2

3

4

Displacement [mm]

0.0

2.5

5.0

7.5

10.0

12.5

15.0

17.5

20.0

Force [N]

A

B

Interface – Fracture Observation

Ceramic

Copper

Cross section (SEM)

I Crack length measurement accuracy: ±50µm

I Crack occurs at interface

I No Al2O3remaining on Cu

I ≈20µm bonding defects Ü To be considered in

Interface – Fracture Observation

Delaminated copper surface (SEM)

I Crack length measurement accuracy: ±50µm

I Crack occurs at interface I No Al2O3remaining on Cu I ≈20µm bonding defects

Ü To be considered in simulation

Interface – Cohesive model

Cohesive model

I OnceTMax has been reached, degradation occurs

I Gradual reduction in stiffness I Eventualy, separation at interface

Implementation [6]

I Simulation of the 4-point test I Cohesive zone between Al2O3and

bottom Cu

I Two parameters: TMax andΦSep

TMax

δ0 _δcr _δ

K

ΦSep

T

(1-D)K [MPa]

Interface – Cohesive model

Cohesive model

I OnceTMax has been reached, degradation occurs

I Gradual reduction in stiffness I Eventualy, separation at interface

Implementation [6]

I Simulation of the 4-point test I Cohesive zone between Al2O3and

bottom Cu

I Two parameters: TMax andΦSep

TMax

δ0 _δcr _δ

K

ΦSep

T

(1-D)K [MPa]

[mm]

Copper

Copper Ceramic

Interface – Model Identification

2 sources of data for model identification

0

1

2

3

4

Displacement [mm]

0

2

4

6

8

10

Force [N]

0.0

0.2

0.4

0.6

0.8

1.0

crack length [mm]

0 1 2 3 4

0

5

10

15

I “Macro” observation

I focus on “peeling” region

Crack length

Interface – Model Identification

2 sources of data for model identification

0

1

2

3

4

Displacement [mm]

0

2

4

6

8

10

Force [N]

0.0

0.2

0.4

0.6

0.8

1.0

crack length [mm]

0 1 2 3 4

0

5

10

15

I “Macro” observation I focus on “peeling”

region

Crack length

Interface – Model Identification

2 sources of data for model identification

0

1

2

3

4

Displacement [mm]

0

2

4

6

8

10

Force [N]

0.0

0.2

0.4

0.6

0.8

1.0

crack length [mm]

Force-Displacement

I “Macro” observation I focus on “peeling”

region

Crack length

Interface – Model Identification

2 sources of data for model identification

0

1

2

3

4

Displacement [mm]

0

2

4

6

8

10

Force [N]

Force Crack length

0.0

0.2

0.4

0.6

0.8

1.0

crack length [mm]

Force-Displacement

I “Macro” observation I focus on “peeling”

region

Crack length

Interface – Model Identification (2)

0 1 2 3 4

Displacement [mm] 4

6 8 10 12

Force [N]

Sep= 32 J/m2 no defect

Measurement

Tmax=350 MPa

Tmax=300 MPa

Interface – Model Identification (2)

0 1 2 3 4

Displacement [mm] 4 6 8 10 12 Force [N]

Sep= 32 J/m2 no defect

Measurement

Tmax=350 MPa

Tmax=300 MPa

Tmax=250 MPa

2.0 2.5 3.0 3.5 4.0

Displacement [mm] 0.00 0.25 0.50 0.75 1.00 1.25 1.50 1.75 2.00

crack length [mm]

Sep= 32 J/m2 no defect

Measurement

Tmax=250 MPa

Tmax=300 MPa

Tmax=350 MPa

Interface – Model Identification (2)

0 1 2 3 4

Displacement [mm] 4 6 8 10 12 Force [N]

Sep= 32 J/m2 no defect

Measurement

Tmax=350 MPa

Tmax=300 MPa

Tmax=250 MPa

2.0 2.5 3.0 3.5 4.0

Displacement [mm] 0.00 0.25 0.50 0.75 1.00 1.25 1.50 1.75 2.00

crack length [mm]

Sep= 32 J/m2 no defect

Measurement

Tmax=250 MPa

Tmax=300 MPa

Tmax=350 MPa

0 1 2 3 4

Displacement [mm] 4 6 8 10 12 Force [N]

Sep= 10 J/m2 20 µm defect

Measurement

Tmax=350 MPa

Tmax=400 MPa

Tmax=450 MPa

Tmax=500 MPa

Interface – Model Identification (2)

0 1 2 3 4

Displacement [mm] 4 6 8 10 12 Force [N]

Sep= 32 J/m2 no defect

Measurement

Tmax=350 MPa

Tmax=300 MPa

Tmax=250 MPa

2.0 2.5 3.0 3.5 4.0

Displacement [mm] 0.00 0.25 0.50 0.75 1.00 1.25 1.50 1.75 2.00

crack length [mm]

Sep= 32 J/m2 no defect

Measurement

Tmax=250 MPa

Tmax=300 MPa

Tmax=350 MPa

0 1 2 3 4

Displacement [mm] 4 6 8 10 12 Force [N]

Sep= 10 J/m2 20 µm defect

Measurement

Tmax=350 MPa

Tmax=400 MPa

Tmax=450 MPa

Tmax=500 MPa

2.0 2.5 3.0 3.5 4.0

Displacement [mm] 0.00 0.25 0.50 0.75 1.00 1.25 1.50 1.75 2.00

crack length [mm]

Sep= 10 J/m2 20 µm defect

Measurement

Tmax=350 MPa

Tmax=400 MPa

Tmax=450 MPa

Tmax=500 MPa

Interface – Model Identification (3)

TMax

[M

Pa

]

No defect

10 20 30

Separation energy Sep [J/m2]

300 350 400 450 500

TMax

[M

Pa

]

With 20 m defect

Fits force/displacement measurement Fits optical measurement

I Simulation for various:

I Φ_Sep(separation energy)

I TMax (crack initiation stress)

I With or without defects

I A suitable parameter set fits

I “Macro” measurements (Force/Displacement)

I “Micro” measurements (Crack length)

Outline

Introduction

Characterization of the copper layers

Characterization of the Ceramic Layer

Characterization of the Metal-Ceramic Interface

Example of simulation results

Delaminated area after 100 cycles (-50/+250°C)

0

1

2

3

4

t

/t

0.00

0.02

0.04

0.06

0.08

0.10

0.12

Fractured surface [mm²]

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

I Simulation predicts a strong effect of dimples I Weakest configuration expected to bet_Cu =t_Cera

Simulation of the behaviour of a DBC structure

I We identified models for

I Copper: behaviour very specific because of bonding process

I Ceramic: must take into account material grades

I Interface: innovative approach with identifications at macro and micro scales

I Theses models have been used for

I Evaluation of impact of stress-relaxation effects

I Identification of robust Cu/Al2O3/Cu configurations

I Evaluation of robustness to thermal cycling

Simulation of the behaviour of a DBC structure

I We identified models for

I Copper: behaviour very specific because of bonding process

I Ceramic: must take into account material grades

I Interface: innovative approach with identifications at macro and micro scales

I Theses models have been used for

I Evaluation of impact of stress-relaxation effects

I Identification of robust Cu/Al2O3/Cu configurations

I Evaluation of robustness to thermal cycling

Simulation of the behaviour of a DBC structure

I We identified models for

I Copper: behaviour very specific because of bonding process

I Ceramic: must take into account material grades

I Interface: innovative approach with identifications at macro and micro scales

I Theses models have been used for

I Evaluation of impact of stress-relaxation effects

I Identification of robust Cu/Al2O3/Cu configurations

I Evaluation of robustness to thermal cycling

Bibliography I

J. Schulz-Harder, “Ceramic substrates and micro channel cooler,” inECPE Seminar: 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 copper substrate for power electronics applications,”Microelectronics Reliability, 2017. A. Ben Kaabar,Durabilité des assemblages métal céramique employés en électronique 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 physical constants.

American Geophysical Union, 1995.

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

Thank you for your attention.

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