Integrated Design Needs from A Power Electronics Reliability Perspective

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

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

4. Drive & Motor Automation System Rockwell Automation - Allen Bradley 1336 Force Drive Performance Metrics: • Power Density • Cost • Reliability 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 Reliance Electric AC Motor

5. Generic Electronic Packaging Technology Parameters Controlled Power Density (W/m3) High Power Requirements from Devices High Packaging Densities Weight Requirements Cost ($/Function) Reliability (MTBF)

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

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

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

9. Nf DTj Wirebonds in Power Modules Ref.: E. Wolfgang, PCIM Conference 1999 (Nuremberg)

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

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

12. Power Range vs. Thermal Management Approach (Motor Drives) - 2000 HP (kW) Range of Motor Package Heat sink type 0.5 - 1 (0.4 - 0.75) Discrete None 1 - 5 (0.75 - 3.7) Discrete Forced/Natural Air cooled 5 - 40 (3.7 - 30) 6-Pack Module Forced Air cooled 40 - 150 (40 - 113) Parallel Discrete Modules Forced Air cooled 150 - 500+ (113 - 375+) Parallel Discrete Modules/ Press-pack Forced Air or Water cooled

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

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. Baseplate Power Density ~ 105 W/m2 T fin = 55C Silicon Power Density = 106 W/m2 Silicon Tj ~125-150 C Heatsink Power Density ~ 103 W/m2 Decrease in System Volume Through Utilization Of Silicon Carbide (SiC) Electronics Baseplate Power Density ~ 105 W/m2 SiC Power Density = 106 W/m2 T fin >200C Silicon Carbide Tj ~300 - 350 C Smaller, hotter heatsink feasible with SiC (Q=hADT) Heatsink Power Density ~ 104 W/m2

16. Conclusions • • Advantages of new power electronics designs must be demonstrated at the system level. • Device Power Density (A/cm2 or W/cm2 ) • System Power Density (W/m3) • 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