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.