IGBT Power Module for HEV and EV

Dr. Birol SonuparlakTom SleasmanMarch 8, 2011

March 8, 2011 22

A Global Leader In Specialty Materials Based Solutions for A World Of Applications Demanding Exceptional Performance and Reliability

Printed Circuit Materials

Power Electronic Solutions

High Performance Foams

March 8, 2011 3

INTRODUCTION

• HEV/EV Market and Motivation• Engineered Materials Developed for IGBT

Power Module Cooling– Baseplate selection– Cooling systems– Joining processes in Power Module manufacturing

• Pin Heat sink/Baseplate Plating/Coating Options• Solder Selection• Joining

• Summary

March 8, 2011 4

EV/HEV Motivation

• Reduced Fuel Consumption– Electric motor assists the Internal Combustion Engine (ICE) to reduce

fuel consumption as vehicle starts & accelerates.– No ICE in EV

• Improved Performance– Electric motors deliver maximum torque from zero rpm for powerful

start and added power for acceleration. • Environmental Performance

– Reduced or eliminated CO2 emissions improves environmental performance through reduced fuel consumption.

March 8, 2011 5

Improvements Implemented by HEV/EV Power Module Technology

Traction Type Power Module• 5 mm AlSiC baseplate• Lead free solder preform• Vacuum Soldering • Grease interface between baseplate and Heat sink

• Nickel plating

Automotive Power Module• 3mm AlSiC pin heat sink• Lead free solder paste• Eliminate vacuum soldering• Eliminated grease interface• Ni plating or copper cold gascoating

March 8, 2011 6

Materials Used to Remove Heat in IGBT Modules

COEFFICIENT OF THERMAL EXPANSION (PPM/K)-5 0 5 10 15 20 25

THE

RM

AL

CO

ND

UC

TIV

ITY

(W/m

-K)

100

200

300

400

500

600

SiAl

Cu/W

Cu/MoAluminum

CTE OF Si, SiC, Al2 O3 ,AlN, Si3 N4

Copper

Cu/Mo/CuAlSiC

Rogers HEATWAVETM

700

AlN

Al2 O3

Si3 N4

March 8, 2011 7

Copper Heat Sink vs AlSiC Heat Sink in HEV/EV IGBT Power Module

AlSiC Pin Heat Sink Copper Pin Heat Sink

Manufacturing process Pressure Infiltration casting Metal Injection Molding

Substrate Aluminum Nitride Aluminum Oxide

PerformanceAlSiC Pin Heat Sink/AlN combination has better performance than

Copper Heatsink/Alumina Combination

Pin Shape Round, Diamond & more Round, Diamond & more

Pin density More Pin density in copper

Pin Height 3.5 mm 7 mm

Thermal Conductivity (W/m-K) 180-240 400

CTE (ppm/K) 8 17

Density 3 g/cc 8.9 g/cc

Weight 213mmx92mmx3mm 3.5mm pin height 245 g 726 g

March 8, 2011 8

Effect of Thermal Cycling

• Due to closer match of CTE’s between AlSiC (CTE=7 ppm/K) and AlN (CTE=4.5 ppm/K) no delamination is observed in the solder layer between ceramic substrate and AlSiC baseplate even after 20000 thermal cycles (ΔT=80oC), while clear solder failure is observed when the baseplate is copper (CTE=17 ppm/K)

Courtesy of Infineon Technologies AG

March 8, 2011 9

100 µm 25 µm

ALUMINUM

SiC

HEATWAVETM AlSiC Microstructure Used in Current IGBT Modules

March 8, 2011 10

AlSiC CTE Model

Silicon

Aluminum

Copper

LTCC

Alumina

AlN

ROGERS HEATWAVETMAlSiC

March 8, 2011 11

AlSiC Thermal Conductivity

Thermal Conductivity Variation w/Thermal diffusivity

100.0

120.0

140.0

160.0

180.0

200.0

220.0

0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.85 0.9 0.95 1

Thermal Diffusivity (J/cm)

Ther

mla

Con

duct

ivity

(W/m

-K)

Thermal Conductivity Variation w/ Density

100.0

140.0

180.0

220.0

2.900 2.950 3.000 3.050 3.100

Density (g/cc)

Ther

mal

Con

duct

ivity

(W/m

-K)

March 8, 2011 12

Liquid Cooling Systems

• Cold Plates– Machined or extruded aluminum plates with or without inserted copper

tubes– Need to use grease as thermal interface materials

• Pin Fins– Copper, AlSiC or aluminum pin heat sinks with various pin geometries– Eliminates the need for thermal interface materials

• ShowerPower– Eliminates the need for pin fin– More homogeneous cooling– Bulging of baseplates is a problem when high pressure is required

• Liquid Cooled DBC Substrate– Cooling channels are integrated directly to DBC– Eliminates baseplate – Produced by joining various copper layers with different hole pattern to

DBC

March 8, 2011 13

Pin Fin Cooling

• Efficient cooling system• Broad variety of pin geometries• CTE Match to DBC Substrate• High thermal conductivity for heat

dissipation• Tight dimensional tolerances without

machining

March 8, 2011 14

Danfoss ShowerPower®

• CTE match to DBC substrate• High thermal conductivity for heat dissipation• Homogeneous cooling• Cooling can be tailored• Good thermal performance at a low pressure drop

Courtesy of Danfoss Silicon Power GmbH

March 8, 2011 15

Liquid Cooled DBC Substrate

March 8, 2011 16

Soldering AlSiC Baseplate to DBC

• Solder Options– Solder paste– Solder Preform

• Solder Compositions– Sn-37Pb– Sn-3.5Ag– Sn-3Ag-0.5Cu

• Soldering reflow Profile– 15oC to 30oC above the melting point of solder composition

• Baseplate surface Finish– Nickel plating– Copper Cold Gas Coating

March 8, 2011 17

Solder Preform versus Solder Paste

Solder Paste• No fixture Required• Low cost/Large Volume

adaptable using screen printing

• Solder Void is >5%• Requires cleaning in most

cases• Inert gas continuous soldering

is possible• Both Sn-Pb and lead free

solder pastes are available• Shelf life and specific Storage

conditions exist

Solder preform• Soldering fixture is required for

locating preform• Requires solder preform

cutting/coining is required• Solder void <5%• Requires vacuum soldering

and soldering is batch process• Both Sn-Pb and Lead free

solders are available• No solder preform life issues

March 8, 2011 18

Criteria For Solder Joining to AlSiC Pin Heat Sink Using Wetting Angle

Very GoodWetting angle <10o

Very Good to AcceptableWetting angle =10o-20o

Not AcceptableWetting angle >20o

March 8, 2011 19

Solderability with various Solders

Copper Cold Gas CoatingSolder Paste-Sn-3Ag-0.5CuContact Angle <10o

Electroless Ni PlatingSolder Preform-Sn-3Ag-0.5CuContact Angle <10o

Electroless Ni PlatingSolder Preform-Sn-37PbContact Angle <10o

March 8, 2011 20

Alternative Available AlSiC Compositions

CTE = 12 ppm/KTC = 183 W/m-K

CTE = 5.3 ppm/KTC = 230 W/m-K

March 8, 2011 21

Thermal Management Materials Used in IGBT Modules

COEFFICIENT OF THERMAL EXPANSION (PPM/K)-5 0 5 10 15 20 25

THE

RM

AL

CO

ND

UC

TIV

ITY

(W/m

-K)

100

200

300

400

500

600

Aluminum

CTE OF Si, SiC, Al2 O3 ,AlN, Si3 N4

Copper

Diamond/AlDiamond/Cu

AlSiC 8

Aluminum Encapsulated ScD

Rogers HEATWAVETM

AlSiC 5

700

ScD

AlN

Al2 O3

Si3 N4

March 8, 2011 22

Continuous Improvement In IGBT Power Module design

Performance Improvement• IGBT semiconductor performance at

junction temperature above 200oC.• Increasing Tj,op from 125oC to 175oC

allows to combustion engine coolant to cool the power electronics w/o need of a separate cooling circuit.

• Improved reliability in joining technologies. At Tj,op= 175oC, solder fatigue and wire bond lift-off failures limit power cycling/thermal shock lifetime.

Material Challenges• Lower cost water cooled integrated

heat sink• High reliability MMC/ceramic

combination with good thermal performance

AlSiC or Copper

Currrent

Eliminate Solder Joints

Future

March 8, 2011 23

Hybrid Composites

AlN in-situ joined to AlSiC

CeramicCeramics in-situ Joined to AlSiC

Aluminum Joint Between Ceramic and AlSiC

March 8, 2011 24

Summary

• HEATWAVETM AlSiC CTE and Thermal Conductivity can be Tailored to Meet Application Requirements– CTE – 5 ppm/K to 15 ppm/K– TC – As High as 230 W/m-K

• HEATWAVETM Hybrid Composites Allow Designers to use AlSiC for Applications Which Require Very High Heat Dissipation.

• Pressure Infiltration Process can be Utilized to Design Hybrid Composites for Various Unique Applications.