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
1 / 29
Outline
Introduction
Characterization of the copper layers
Characterization of the Ceramic Layer
Characterization of the Metal-Ceramic Interface
Conclusion
2 / 29
Outline
Introduction
Characterization of the copper layers
Characterization of the Ceramic Layer
Characterization of the Metal-Ceramic Interface
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 – 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
Characterization of the copper layers
Characterization of the Ceramic Layer
Characterization of the Metal-Ceramic Interface
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 – 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 – 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 – 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])
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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
Characterization of the copper layers
Characterization of the Ceramic Layer
Characterization of the Metal-Ceramic Interface
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.
12 / 29
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
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Outline
Introduction
Characterization of the copper layers
Characterization of the Ceramic Layer
Characterization of the Metal-Ceramic Interface
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
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
B
19 / 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
B
19 / 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
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
20 / 29
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 1 2 3 4Displacement [mm]
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
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Interface – Model Identification
2 sources of data for model identification
0 1 2 3 4Displacement [mm]
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
Interface – Model Identification
2 sources of data for model identification
0 1 2 3 4Displacement [mm]
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
Interface – Model Identification
2 sources of data for model identification
0 1 2 3 4Displacement [mm]
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)
0 1 2 3 4Displacement [mm]
4
6
8
10
12
Forc
e [N
]
Sep = 32 J/m2
no defect
MeasurementTmax=350 MPaTmax=300 MPaTmax=250 MPa
23 / 29
Interface – Model Identification (2)
0 1 2 3 4Displacement [mm]
4
6
8
10
12
Forc
e [N
]
Sep = 32 J/m2
no defect
MeasurementTmax=350 MPaTmax=300 MPaTmax=250 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 = 32 J/m2
no defectMeasurementTmax=250 MPaTmax=300 MPaTmax=350 MPa
23 / 29
Interface – Model Identification (2)
0 1 2 3 4Displacement [mm]
4
6
8
10
12
Forc
e [N
]
Sep = 32 J/m2
no defect
MeasurementTmax=350 MPaTmax=300 MPaTmax=250 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 = 32 J/m2
no defectMeasurementTmax=250 MPaTmax=300 MPaTmax=350 MPa
0 1 2 3 4Displacement [mm]
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
Interface – Model Identification (2)
0 1 2 3 4Displacement [mm]
4
6
8
10
12
Forc
e [N
]
Sep = 32 J/m2
no defect
MeasurementTmax=350 MPaTmax=300 MPaTmax=250 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 = 32 J/m2
no defectMeasurementTmax=250 MPaTmax=300 MPaTmax=350 MPa
0 1 2 3 4Displacement [mm]
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
Interface – Model Identification (3)
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
Characterization of the copper layers
Characterization of the Ceramic Layer
Characterization of the Metal-Ceramic Interface
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
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
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).
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