1. Integrated Design Needs from A Power Electronics Reliability Perspective Mike Shaw, Jun He, Vivek Mehrotra, Fred Morris, Bruce Beihoff, Rich Lukaszewski, Sriram Chandrasekeran and Qingda Yang July 19, 2000

2. 2 Relevant Electronic Package Examples Power Modules, Chip-Scale Packages RF Power Packages Focal Plane Arrays dc-dc Converters Interposer PC Board Semiconductor Chip (1-2 mm) Metal Baseplate/ Heatsink Ceramic Isolation Layer Silicone Encapsulant Wirebonds Semiconductor Chip (multiple @ 1 cm) Semiconductor Chip (5-20 mm) Ceramic Carrier Wirebonds Metal Baseplate/ Heatsink Wirebonds Overfill Solder Joints > 1000 V< 5 V< 50 V< 20 V > 1000 A< 5 A< 20 A < 10 A ~ kHzMHzGHzkHz - MHz - 40 / +150 C - 40 / +150 C - 40 / +150 C - 77 / +60 C Today’s Focus Semiconductor Chip (~20mm)

3. 3 Motor Drives Radar / Microwave Communications dc to dc Converters Power Supplies Electric Vehicle Drives Weapons Systems Power Electronic Systems Today’s Topics

4. 4 Converts AC power (fixed frequency, voltage) to AC Power (variable frequency, current, and voltage) Enables exact control of speed (RPM) and torque of motors Motors become controlled electromechanical energy converters. Rockwell Automation - Allen Bradley 1336 Force Drive Rockwell Automation Reliance Electric AC Motor Drive & Motor Automation System Performance Metrics: Power Density Cost Reliability

5. 5 Generic Electronic Packaging Technology Parameters Controlled Power Density (W/m 3 ) High Power Requirements from Devices High Packaging Densities Weight Requirements Cost ($/Function) Reliability (MTBF)

6. 6 Lifetime Estimation of Critical Importance 1) Silicon Failure 2) Wirebond Failure 3) Solder/Attachment Failure 4) Encapsulant Failure 5) Substrate Failure Most Failure Mechanisms are Thermally Activated or Enhanced Primary Failure Modes in Si-IGBT Power Modules Example in Power Electronics Communications: Friend-or-foe Interrogation by Microwave Transmission….

7. 7 Typical Coupled Predictive/Experimental Reliability Approach Assume: 1) T j measured through V CE or V GE methods; 2) T c, T a measured with a thermocouple method; 3) All T j, T c, T a measurements recorded automatically throughout the experiments 4) Power is DC excitation only Case Temp, T c Time, t T c, maximum T c, minimum TcTc 300 sec 30 sec Figure TjTj T j, maximum Detailed, 3D Numerical Analyses Contrasted with Experimental Power-HALT Analyses Are Either/Both Correct? Copper Post Silicon Solder Strain Concentration and Crack Initiation Point Predicted Crack Propagation Path

8. 8 E.g., Power Electronics Lifetime Governed by Temperature Swing During Operation Ref: K. Sommer, eupec GmbH + Co, Trodheim, 1997. KF4 Power Modules

9. 9 Ref.: E. Wolfgang, PCIM Conference 1999 (Nuremberg) TjTj NfNf Wirebonds in Power Modules

10. 10 Thermal Cycling of Sn - Pb Joints (Elastic/Plastic) As Soldered 1 cycle 10 cycles 100 cycles 1000 cycles Copper Kovar  = 14.1 ppm  = 2.7 ppm Cu or Kovar Si Sn-Pb Solder Crack within Solder Layer He et al Reliability at “Effects of Plasticity on Reliability in Multilayered Electronic Packages,” ITHERM Conference Proceedings, in press, Las Vegas, 5/00.

11. 11 Motor / Load Essential Motor Drive Components Control Interface Power Supply (low power) Gate Driver Board Control Board Power Supply, High Power Power Module Heatsink Control Signals Antenna RF Power Power Transistors (RF Power Analogy)

12. 12 Power Range vs. Thermal Management Approach (Motor Drives) - 2000 HP (kW) Range of MotorPackageHeat sink type 0.5 - 1 (0.4 - 0.75)DiscreteNone 1 - 5 (0.75 - 3.7)Discrete Forced/Natural Air cooled 5 - 40(3.7 - 30)6-Pack ModuleForced Air cooled 40 - 150(40 - 113)Parallel Discrete Modules Forced Air cooled 150 - 500+(113 - 375+)Parallel Discrete Modules/ Press-packForced Air or Water cooled

13. 13 Experimental Measurements of Device Temperature Distributions by IR microscopy - Power Transistors in Motor Drives The magnitude as well as gradient of T j needs to be reduced J. He, V. Mehrotra and M.C. Shaw, “Thermal Design and Measurement of IGBT Power Modules: Transient and Steady-State, IEEE IAS Conference Proc., 34 th Annual Mtg., Phoenix, Az, 10/99.

14. 14 Wide Range of Application Profiles Complicate Reliability Analyses Pumps Fans Radar Protocols…………. What are the consequent thermal, mechanical loads over a 20-year life?

15. 15 Decrease in System Volume Through Utilization Of Silicon Carbide (SiC) Electronics Silicon Power Density = 10 6 W/m 2 Baseplate Power Density ~ 10 5 W/m 2 Heatsink Power Density ~ 10 3 W/m 2 T fin = 55C Silicon Tj ~125-150 C SiC Power Density = 10 6 W/m 2 Baseplate Power Density ~ 10 5 W/m 2 Heatsink Power Density ~ 10 4 W/m 2 T fin >200C Silicon Carbide Tj ~300 - 350 C Smaller, hotter heatsink feasible with SiC (Q=hA  T)

16. 16 Conclusions Advantages of new power electronics designs must be demonstrated at the system level. Device Power Density (A/cm 2 or W/cm 2 ) System Power Density (W/m 3 ) Lifetime Assurance of Entire System System Cost Analysis Ultimately Required Highly localized heating around active cell regions leads to sharp temperature gradients. Complex interactions occur between electronics function, thermal loads and physical failure mechanisms Integrated Design Methodology Needs: - Cellular design methodology yields ideal design process - Closed loop electrical, thermal, mechanical coupling essential - Well-established (calibrated), physically-based reliability models required - Statistical distributions of failures critical - Self-optimization schemes offer enormous potential