Integrated Design Needs from A Power Electronics Reliability Perspective

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

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Relevant Electronic Package Examples

Power Modules, Chip-Scale Packages RF Power Packages Focal Plane Arraysdc-dc Converters

Interposer

PC Board

Semiconductor Chip (1-2 mm)

MetalBaseplate/Heatsink

CeramicIsolation

Layer

SiliconeEncapsulant Wirebonds

Semiconductor Chip(multiple @ 1 cm) Semiconductor

Chip (5-20 mm)

Ceramic Carrier

WirebondsMetalBaseplate/Heatsink

WirebondsOverfill

Solder Joints

> 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

Semiconductor Chip (~20mm)

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• Motor Drives

• Radar / Microwave Communications

• dc to dc Converters

• Power Supplies

• Electric Vehicle Drives

• Weapons Systems

Power Electronic Systems

Today’s Topics

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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 AutomationReliance Electric AC Motor

Drive & Motor Automation System

Performance Metrics: • Power Density • Cost • Reliability

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Generic Electronic Packaging Technology Parameters

Controlled Power Density (W/m3)High Power Requirements from DevicesHigh Packaging DensitiesWeight Requirements

Cost ($/Function)

Reliability (MTBF)

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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….

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Typical Coupled Predictive/Experimental Reliability Approach

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 experiments4) Power is DC excitation only

Cas

e T

emp,

Tc

Time, t

Tc, maximum

Tc, minimum

Tc

300 sec

30 sec

Figure

Tj

Tj, 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

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E.g., Power Electronics Lifetime Governed by Temperature Swing During Operation

Number of cycles

10.000

100.000

1.000.000

10.000.000

30 40 50 60 70 80 90 100

delta Tj (°C)

heel crack

diode bonds

FZ1200R16, LotA, failed 2/6, Tj=60°C_100°C

FZ1200R16, LotA, failed 2/6, Tj=60°C_120°C

FZ1200R16, Lot B, failed 3/3, Tj=75°C_125°C

FZ1200R33, Lot C, failed 2/2, Tj=46°C_112°C

FZ1200R33, Lot D, failed 1/1, Tj=49°C_127°C

estimated trend <10% failure rate

estimated trend =50% failure rate

Ref: K. Sommer, eupec GmbH + Co, Trodheim, 1997.

KF4 Power Modules

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Si, 2,6 10-6 K-1

Al, 23,8 10-6 K-1

crack

Ref.: E. Wolfgang, PCIM Conference 1999 (Nuremberg)

Tj

Nf

Wirebonds in Power Modules

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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

SiSn-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.

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Motor / Load

Essential Motor Drive Components

ControlInterface

Power Supply(low power)

Gate DriverBoard

Control Board

Power Supply,High Power

PowerModule

Heatsink

Control Signals

Antenna

RF Power

PowerTransistors

(RF Power Analogy)

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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

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Experimental Measurements of Device Temperature Distributions by IR microscopy - Power Transistors in Motor Drives

The magnitude as well as gradient of Tj needs to be reduced

139 C

131 C

127 C117 C

124 C

119 C

122 C

137 C127 C

130 C

134 C

123 C117 C

122 C

133 C

130 C124 C

120 C116 C

118 C

132 C

129 C

126 C

121 C119 C

112 C

120 C

134 C137 C

132 C

127 C

131 C

120 C

117 C

124 C

138 C132 C

131 C

129 C

122 C

115 C

141 C

138 C

137 C

134 C123 C

125 C

135 C

124 C

130 C

129 C

126 C

119 C

120 C

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.

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Wide Range of Application Profiles Complicate Reliability Analyses

• Pumps• Fans• Radar Protocols………….

• What are the consequent thermal, mechanical loads over a 20-year life?

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Decrease in System Volume Through Utilization Of Silicon Carbide (SiC) Electronics

Silicon PowerDensity = 106 W/m2

Baseplate Power Density ~ 105 W/m2

Heatsink Power Density ~ 103 W/m2

T fin = 55C

SiliconTj ~125-150 C

SiC PowerDensity = 106 W/m2

Baseplate Power Density ~ 105 W/m2

Heatsink Power Density ~ 104 W/m2

T fin >200C

Silicon CarbideTj ~300 - 350 C

Smaller, hotter

heatsink feasiblewith SiC

(Q=hAT)

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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 SystemSystem 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