Modelling Reliability of Power Electronics Modules Current Status and Future Challenges Prof Chris Bailey University of Greenwich

Transcription

1 Modelling Reliability of Power Electronics Modules Current Status and Future Challenges Prof Chris Bailey University of Greenwich Department of Electrical and Electronic Engineering

2 Contents University of Greenwich Fatigue in Power Electronics Finite Element Modelling Examples Centre Projects Future Challenges Department of Electrical and Electronic Engineering

3 Greenwich within the Centre 3

4 Analysis Tools at Greenwich Thermal, Fluids, Chemical Flotherm, Comsol, FLUENT, Phoenics, CFX PHYSICA (In-House Code) Airflow Temperature Mechanical ANSYS, COMSOL, PHYSICA Electrical + Optical Tracepro, EMAG, PHYSICA Multi-Physics Analysis Die #3 Die #2 Die #1 Stress Multi-Physics PHYSICA, Comsol, Ansys Other MD (In-house software) Evolver Multi-Scale Analysis Optical Analysis Surface Tension & Microstructure Tools

5 Analysis Tools at Greenwich Optimisation & Risk Analysis Visual Doc, ROMARA Reliability & Prognostics RELEX, ROMARA, Powerlife Windows & Linux Cluster Optimisation & Process Capability PXI Hardware in Loop Embedded Systems Parallel Computing Reliability/Prognostics

6 Contents University of Greenwich Fatigue in Power Electronics Finite Element Modelling Examples Centre Projects Future Challenges Department of Electrical and Electronic Engineering

7 Bathtub Curve Department of Electrical and Electronic Engineering

8 Fatigue Material degradation Due to cyclic loading Low Cycle Fatigue Strain dominated Coffin Manson High Cycle Fatigue Stress Dominated pl b N a( ) Basquin equation b N S a 1 Department of Electrical and Electronic Engineering

9 Causes of failure Major Causes of Electronics Failures 20% Vibration 6% Dust 55% Temperature 19% Humidity (Source : US Air Force Avionics Integrity Program) 9

10 What causes the Fatigue Cracks? Every time a device is switched on/off it s temperature increases/decreases Alumina CTE = 6 ppm/ C Plastic deformation Ductile Fracture FR4 CTE = 18 ppm/ C

11 Material Properties ALG vs Different materials Thermal performance From Hoffmann Elektrokohle 11

12 Contents University of Greenwich Fatigue in Power Electronics Finite Element Modelling Examples Centre Projects Future Challenges Department of Electrical and Electronic Engineering

13 Why Use Virtual Prototyping Incentive for virtual prototyping tools: MONEY!!! The cost of repairing mistakes increases roughly an order of magnitude at each critical phase. $1,000,000 > 91.4 $100,000 $1,000 $10,000 Design Prototype Production Field

14 Physics of Failure based Reliability 14

15 Steps in FEA CAD MESHING ANALYSIS - VISUALISATION

16 Stress Analysis FEA Tools

17 Predicting Damage CFD, FEA, Optimisation Analysis, etc Boundary + Loading conditions Material Behaviour Temperature, Stress Damage Model Failure Criteria Failure definition Validation What is dominant failure mechanism? How long will the product last?

18 d dt s Solder Creep Model A Q kt n a sinh exp 18

19 Lifetime Models Test Condition Application Life Time Model Notes Thermal Cycling Vibration Drop/Impact Voltage SnAgCu solder Eutectic solder Sn1.2Ag0.5Cu0.05Ni solder Soldered Transistors N f acc N f w 66.3N 75.1N t D f D f w f e C 0 E kt a j acc p e p C V 1 V cb cb max acc = Accu. Creep Strain Hyperbolic Sine Creep w acc = Accu. Energy Density (MPa) Hyperbolic Sine Creep = Stress in MPa N = Cycles to failure = Stress in MPa N = Cycles to failure p = Plastic Strain per drop D f = No. of drops to failure W p = Plastic Work per drop D f = No. of drops to failure t f = Time to failure r = Relative humidity V cb = collector base voltage V cbmax = max. Allowable collector base voltage (Kemeny Model) 19

20 Accuracy of FEA/PoF Modelling Ref: Syed, SEM 20

21 Contents University of Greenwich Fatigue in Power Electronics Finite Element Modelling Examples Centre Projects Future Challenges 21

22 Thermal Cycling Temp ( C) Graph showing the temperature profile for each thermal cycle Cycle A 150 Cycle B Cycle C 100 Cycle D 50 Cycle E Cycle F Time (s) Cycle Low Temp High Temp Ramp Dwell Total Period [ C] [ C] [ C/min] [min] [min] A B C D E F

23 Simulation of Cycle A

24 Comparison with Test FEA Modelling Average creep energy density Average accumulated effective creep strain Damage SnAgCu Experiment Strain Energy A B C D E F Cycle Experiment Drop in Ultimate Shear Strength over 1200 cycles

25 Damage Modelling Cohesive Zone / Disturbed State Creep strain energy density 25

26 Eurofighter Avionics Component PBGA COTS Component Field Life - 25 Years. Middle East (Hot) Europe (Mild) Artic (Cold) Flight/Non Flight Cycles Cycle 6 : Flight Artic / Ambient - 31 C Cycle # 6 26

27 Computational Model Thermal Analysis Full 3D CFD model Stress Analysis 3D Slice Finite Element Material Properties Solder is Viscoplastic Substrate orthotropic All other materials Elastic Failure Mode Fatigue in Solder 27

28 Underfills 28

29 Crack Growth Rate Physics of Failure Model Crack Growth Rate for cycle number ( i) Ri (2.58*10 ) W m / Cycle W is the creep strain energy Failure Criteria Joint fails if crack length > half joint diameter Reference: R Darveaux, Effect of Simulation Methodology on Solder Joint Crack Growth Correlation, Proceedings of 50 th Electronic Components and Technology Conference (2000), pp

30 Modelling Informing Testing Accelerated test cycle How many ALT cycles give same crack length as predicted in the field (25 year life) ATC # Temperature Extremes Failure Free Cycles (FFC) (Based on Crack Growth Criteria) Test Time for FFC (days) 1-32 to 70 C to 70 C to 70 C to 100 C to 125 C Number of Cycles Failure Free Cycles Characteristic Life (N 63.2% ) 6-40 to 125 C to 125 C to 125 C Accelerated Thremal Cycle (#) 30

31 Contents University of Greenwich Fatigue in Power Electronics Finite Element Modelling Examples Centre Projects Future Challenges Department of Electrical and Electronic Engineering

32 DTM Cross Theme Mission Underpinning Research Development of new design methodologies, models and tools that will provide the ability to undertake co-design (device to system) and hence optimise a power electronics system in terms of its efficiency, power density, reliability, robustness, EMI, integration and cost.

33 Components Theme Failure Modelling IGBT s Capacitors Fast Stress Solvers Embedded into PowerLife Underpinning Research D 1 e 0.05 p N f 178L p N f p

34 DTM X-Theme project Underpinning Research 2-Year Project (Started Feb 2015) Methodologies for fast coupled physical-behavioural models for design optimisation

35 Temparature (K) OCM X-Theme Project Underpinning Research Temperature (k) Current Temparature (K) on Diode Chip Load Current (A) Temp on chip (Mo pad) Temp on chip (AlG pad)

36 Contents University of Greenwich Fatigue in Power Electronics Finite Element Modelling Examples Centre Projects Future Challenges Department of Electrical and Electronic Engineering

37 Poor Manufacturing Poor reliability Process Models Process models in Design Department of Electrical and Electronic Engineering 37

38 Reliability PoF Models/Robustness New packaging concepts (IPEM) New materials (Sintered Silver) Acceleration factors Multi-Physics Failure models Monitor failures during operation Design for Robustness

39 Integrated Metrology/Modelling 39

40 Contact Professor Chris Bailey University of Greenwich 40