Characterization of Materials and their Interfaces in a DBC Substrate for Power Electronics Applications ECPE Workshop “Future of Simulation” Aymen B EN K ABAAR 1 , Cyril B UTTAY 2 , Olivier D EZELLUS 3 , Rafaël E STEVEZ 1 , Anthony G RAVOUIL 4 , Laurent G REMILLARD 5 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 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 Ensures ◮ Electrical insulation ◮ Heat conduction 4 / 29
Introduction – Power Electronic Module Ceramic substrate Ensures ◮ Electrical insulation ◮ Heat conduction Direct Bonded Copper ◮ Ceramic: ◮ Heat conduction ◮ Electrical insulation ◮ Patterned Metal: ◮ Forms circuit ◮ Bonding to module 4 / 29
Introduction – Manufacturing of a DBC substrate Copper Ceramic 1080 - Copper Copper O 2 Oxide Ceramic 1070 - Heating Copper 1060 - Eutectic Eutectic Melt Ceramic O 2 Diffusion and 1050 - Cooling 0 0.4 0.8 1.2 1.6 Copper O Concentration in Atom% Ceramic 2 Source: J. Schulz-Harder, Curamic [1] ◮ Standard: Al 2 O 3 /Cu (AlN also possible, with separate oxidation) ◮ Bonding temperature very close to Cu melting point 5 / 29
Introduction – Manufacturing of a DBC substrate Copper Ceramic 1080 - Copper Copper O 2 Oxide Ceramic 1070 - Heating Copper 1060 - Eutectic Eutectic Melt Ceramic O 2 Diffusion and 1050 - Cooling 0 0.4 0.8 1.2 1.6 Copper O Concentration in Atom% Ceramic 2 Source: J. Schulz-Harder, Curamic [1] ◮ Standard: Al 2 O 3 /Cu (AlN also possible, with separate oxidation) ◮ Bonding temperature very close to Cu melting point Objective: modelling of the DBC for thermo-mechanical simulations 5 / 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 process Cu2: The same after DBC annealing (but not bonded to ceramic) ◮ temperature history ◮ no external mechanical stress Cu1: Full DBC process, followed by etching of the ceramic ◮ temp. and mech. history 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 process Cu2: The same after DBC annealing (but not bonded to ceramic) ◮ temperature history ◮ no external mechanical stress Cu1: Full DBC process, followed by etching of the ceramic ◮ temp. and mech. history 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 process Cu2: The same after DBC annealing (but not bonded to ceramic) ◮ temperature history ◮ no external mechanical stress Cu1: Full DBC process, followed by etching of the ceramic ◮ temp. and mech. history 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 process Cu2: The same after DBC annealing (but not bonded to ceramic) ◮ temperature history ◮ no external mechanical stress Cu1: Full DBC process, followed by etching of the ceramic ◮ temp. and mech. history Preparation and test: ◮ Copper sheets supplied by Curamik ◮ samples formed by electro-erosion ◮ Uniaxial and cycling tensile tests 7 / 29
Copper – Tensile test 350 300 Cauchy Stress [MPa] 250 200 150 100 Cu 3 (no annealing) 50 Cu 2 (annealing, free cooling) Cu 1 (Full DBC process) 0 0.00 0.05 0.10 0.15 0.20 0.25 0.30 Log(strain) ◮ Dramatic change caused by annealing (yield stress) ◮ Also, effect of mechanical stress on yield ➜ Further characterization on Cu1, more representative 8 / 29
Copper – Cycling test 120 100 Cauchy Stress [MPa] 80 100 60 75 40 50 25 20 0 0.051 0.052 0.053 0 0.00 0.01 0.02 0.03 0.04 0.05 Log(strain) ◮ Tests on Cu1, repetitive stress 0–120 MPa ◮ No compressive stress to prevent sample from buckling ◮ Ratchet effect caused by kinematic hardening of copper ➜ Need for a suitable model (Armstrong-Fredericks [4]) 9 / 29
Copper – Modelling E C ν σ y γ 127 GPa 0.33 60 MPa 1.7 GPa 14.6 120 Experiment Model 100 ◮ Satisfying modelling of Cauchy Stress [MPa] ◮ Elastic 80 ◮ Plastic ◮ Hardening 100 60 75 Behaviours 40 50 ◮ Parameters identification: 25 ◮ E , ν , σ y : uniaxial tests 20 ◮ C and γ : cycling tests 0 0.051 0.052 0.053 0 0.00 0.01 0.02 0.03 0.04 0.05 Log(strain) 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 ◮ 2 grades of Al 2 O 3 tested: ◮ standard, thickness=635 µ m ◮ “HPS” (Zr-reinforced), thickness=250 µ m ◮ Material supplied by Curamik ◮ Samples cut using a wafer saw ◮ Sample size: 4 mm × 40 mm ◮ 3-point bending test. 12 / 29
Ceramic – Bending Tests 440 Al 2 O 3 FL 3 Zr Al 2 O 3 E = 420 Young's Modulus [GPa] 48 σ wt 3 400 ◮ E : Young’s Modulus 380 ◮ F : maximum load 360 ◮ w : sample width 340 ◮ L : support span 320 ◮ σ : deflection 300 ◮ t : sample thickness 0 5 10 15 20 25 30 Specimen # ◮ good consistency in the results ◮ few defects caused by the sample preparation ◮ good quality of the base material 13 / 29
Ceramic – Bending Tests (2) Weibull Analysis ◮ Considers the sample as a series of elementary volumes ◮ Each volume has a statistical defect probability 2 Al 2 O 3 Zr Al 2 O 3 16.03x-92.59 1 R 2 =0.97 0 log(log(1/ P si )) ◮ P Si : probability of 1 survival 2 ◮ σ w : Weibull stress 18.96x-121 R 2 =0.99 3 4 5.4 5.6 5.8 6.0 6.2 6.4 6.6 log( W ) 14 / 29
Ceramic – Modelling Model used ◮ Purely elastic behavior ◮ Considers rupture Identification of model parameters: ◮ E : from bending test ◮ ν : from literature [5] ◮ m , σ 0 and V eff : from Weibull analysis. E m V eff ν σ 0 0.103 mm 3 Al 2 O 3 403 GPa 0,22 16.03 322 MPa 0.501 mm 3 Zr-Al 2 O 3 330 GPa 0.22 18.95 590 MPa 15 / 29
Outline Introduction Characterization of the copper layers Characterization of the Ceramic Layer Characterization of the Metal-Ceramic Interface Conclusion 16 / 29
Interface – Test Principle ◮ DBC sample with a notch in top Cu ◮ 4-point bending test ◮ Monitoring of fracture propagation ◮ Parameter identification with FE simulation 17 / 29
Interface – Preparation of the samples ◮ DBC configuration: 500 µ m Cu / 250 µ m Zr-Al 2 O 3 / 500 µ Cu ◮ Chemical etching of copper patterns ◮ Ceramic cutting with a wafer saw ◮ Sample size: 10 × 80 mm 2 18 / 29
Interface – Bending Tests 20.0 17.5 A 15.0 12.5 Force [N] 10.0 7.5 5.0 2.5 0.0 0 1 2 3 4 Displacement [mm] 19 / 29
Interface – Bending Tests 20.0 17.5 A 15.0 12.5 Force [N] 10.0 7.5 5.0 B 2.5 0.0 0 1 2 3 4 Displacement [mm] 19 / 29
Interface – Bending Tests 20.0 17.5 A 15.0 12.5 Force [N] 10.0 7.5 5.0 B 2.5 0.0 0 1 2 3 4 Displacement [mm] 19 / 29
Interface – Bending Tests 20.0 17.5 A 15.0 12.5 Force [N] 10.0 C 7.5 5.0 B 2.5 0.0 0 1 2 3 4 Displacement [mm] 19 / 29
Interface – Fracture Observation Ceramic Copper ◮ Crack length measurement accuracy: ± 50 µ m ◮ Crack occurs at interface ◮ No Al 2 O 3 remaining on Cu ◮ ≈ 20 µ m bonding defects ➜ To be considered in simulation Cross section (SEM) 20 / 29
Interface – Fracture Observation ◮ Crack length measurement accuracy: ± 50 µ m ◮ Crack occurs at interface ◮ No Al 2 O 3 remaining on Cu ◮ ≈ 20 µ m bonding defects ➜ To be considered in simulation Delaminated copper surface (SEM) 20 / 29
Interface – Cohesive model T [MPa] T Max Cohesive model ◮ Once T Max has been reached, degradation occurs K (1-D)K Φ Sep ◮ Gradual reduction in stiffness [mm] ◮ Eventualy, separation at interface δ 0 δ cr δ 21 / 29
Interface – Cohesive model T [MPa] T Max Cohesive model ◮ Once T Max has been reached, degradation occurs K (1-D)K Φ Sep ◮ Gradual reduction in stiffness [mm] ◮ Eventualy, separation at interface δ 0 δ cr δ Implementation [6] ◮ Simulation of the 4-point test ◮ Cohesive zone between Al 2 O 3 and bottom Cu Copper ◮ Two parameters: T Max and Φ Sep Ceramic Cohesive zone Copper 21 / 29
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