advanced thermal control enabling cost reduction for
TRANSCRIPT
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Advanced Thermal Control Enabling Cost Reduction for Automotive Power ElectronicsThomas Abraham, Kenneth Kelly, and Kevin BennionNational Renewable Energy Laboratory
Andreas Vlahinos, Advanced Engineering Solutions, LLC
NREL/PR-540-43819Presented at the 2008 ANSYS Automotive Conference sponsored by ANSYS held September 4-5, 2008 in Dearborn, Michigan
This presentation is subject to Government rights.
NREL is a national laboratory of the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, operated by Midwest Research Institute • Battelle.
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Industry and Academia
DOE’s Advanced Power Electronics and Electric Machines (APEEM) Research
Oak Ridge National Laboratory (ORNL)Lead: Power Electronics & Electric Machines R&D
National Renewable Energy Laboratory (NREL)Lead: APEEM Thermal Control R&D
+ Other Industry Partnersand Universities
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Motivation
• Most aggressive target of FreedomCAR program is the cost (2020 target is $8/kW for a 55 kW traction system).
• Meeting the cost target is critical for greater penetration of the vehicles market .
• NREL’s Advanced Power Electronics team is working on next-generation advanced cooling technologies (jets/sprays/micro-channels with single or two-phase) and novel packaging topologies.
• Advanced cooling technologies are used in conjunction with novel packaging topologies for identifying low-cost materials for cost (and weight) reductions while meeting the targets of performance and reliability.
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Description of Technology
TIMDBCsolder
BH
RRRTTQ++
−=
)( Silicon Chip
Solder
Direct Bond CopperCu, AlN, Cu
Thermal Paste
Base Plate, Heat Sink
Pin FinsTB, Base Plate Temp.
TH, IGBT Temp.
TC, Coolant Temp.Q heat
)( CB TTAhQ −=
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Topologies
Baseline TopologyTopology 1 (very similar to the baseline topology, which uses Thermal Interface Material)
Topology 2 (Base plate cooling; does not involve Thermal Interface Material) Topology 3 (Direct Cooling of Direct
Bonded Copper)
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Thermal Materials Exploration Study – Steps
Thermal Materials Exploration Study
Part 1:
Exploring tradeoffs between thermal performance and cost for several topologies
Part 2:Evaluation of Thermal
Stress andReliability Aspects
Part 3:Emerging technologies: 1)LTCC substrates 2)Organic substrates
• Performance: Peak temperatures of the switching devices (IGBTs and diodes) need to be below 150oC.
• Reliability: Power electronics need to meet life-cycle target of 15 years.
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Thermal Materials Exploration Study – Comments
• Two layers that have potential opportunities for cost reduction are the substrate and the cold plate.
• Today’s preferred substrate, Aluminum Nitride (AlN) is expensive.
• Low-cost LTCC technology has been well demonstrated in automotive electronics applications. Several issues, notably thermal disadvantages have slowed down the spread of this substrate technology [1].
• Silicon nitride (SiN) as a substrate would make economic sense if the cost is reduced to $5 per pound [2].
1. Fairchild, M.R., Snyder, R.B., Berlin, C.W., and Sarma, D.H.R., “Emerging Substrate Technologies for Harsh-Environment Automotive Electronics Applications,” SAE 2002-01-1052.
2. Das, S., and Curlee, T.R., “The Cost of Silicon Nitride Powder: What Must It Be To Compete?” 1992, ORNL-6694.
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Materials Exploration – Topology 1
Alternate materials are explored for each layer
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Verification of CFD Model with Test
CFD Test
Average Heat Transfer Coefficient
(W/m2.K) 18,350 18,481
CFD (using Fluent) Test
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”What-If” option of Design Explorer in “ANSYS Workbench Thermal Simulation” is used to automate materials exploration studies
Heat Transfer Coefficient = 18,350 W/(m^2.K)
Coolant Temperature = 105 oC
Heat load per IGBT heat load = 85 WHeat Load per Diode = 35 W
Thermal Conductivity is varied for all the layers according to
the material
kcoldplate ksolder ksubstrate kbaseplate
Bulk material costs are assigned on a volumetric
basis
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Materials combination for cost reduction – Topology 1
Low-cost combination that meets the performance target (Cu-Mo, Graphite, SiN-Ideal)
Cost -> 842 Peak Temp -> 142 OC
Low-cost combination that meets the performance target (Cu-Mo, Graphite, Alumina, an LTCC substrate)
Cost -> 889 Peak Temp -> 149 OC
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Substrate Materials for Cost Reduction – Topology 1
500 1000 1500 2000 2500 3000 3500115
120
125
130
135
140
145
150
155
160
165
170
Cost per IGBT Diode pair*1000 ($)
Max
imum
Tem
pera
ture
(C)
Maximum Temperature Vs Cost Aluminum Nitride AINALN, AL-501ALN, AL-502AL-503AL-504AN75WAlumina, Al203AL203, AL-600AL2O3, AL-601AL2O3, AL-602AL203, AL-603AL2O3, AL-604AL203, AL-605AL2O3, AL-610Boron Nitride, BO-502Silicon Nitride, S1-501Silicon Nitride, IdealBeryllium Oxide (BeO)
Silicon nitride, ideal
Alumina, an LTCC substrate
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Base Plate Materials for Cost Reduction – Topology 1
500 1000 1500 2000 2500 3000 3500115
120
125
130
135
140
145
150
155
160
165
170
Cost per IGBT Diode pair*1000 ($)
Max
imum
Tem
pera
ture
(C)
Maximum Temperature Vs Cost
Copper Cu-Mo Cu-Tungsten AlSiC
Cu-Mo is a candidate base plate material (used in Prius)
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Materials Exploration – Topology 2
• First level text – Arial 28 pt.– Second level text – Arial 28 pt.
• Third level text – Arial 24 pt.– Fourth level text – Arial 22 pt.
• Fifth level text – Arial 20 pt.
Base Plate Cooling
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Materials Combination for Cost Reduction – Topology 2
Low-cost combination that meets the performance target (Cu-Mo, SiN-Ideal)
Cost -> 662 Peak Temp -> 132 OC
Low-cost combination that meets the performance target (Cu-Mo, Alumina, an LTCC substrate)
Cost -> 682 Peak Temp -> 148 OC
Cost with Topology 1 -> 889
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Substrate Materials for Cost Reduction – Topology 2
500 1000 1500 2000 2500 3000 3500115
120
125
130
135
140
145
150
155
160
165
170
Cost per IGBT Diode pair*1000 ($)
Max
imum
Tem
pera
ture
(C)
Maximum Temperature Vs Cost
Aluminum Nitride AINALN, AL-501ALN, AL-502AL-503AL-504AN75WAlumina, Al203AL203, AL-600AL2O3, AL-601AL2O3, AL-602AL203, AL-603AL2O3, AL-604AL203, AL-605AL2O3, AL-610Boron Nitride, BO-502Silicon Nitride, S1-501Silicon Nitride, IdealBeryllium Oxide (BeO)
Silicon nitride, ideal
Alumina, an LTCC substrate
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Materials Exploration – Topology 3
Direct Cooling of Direct Bonded Copper
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Materials Combination for Cost Reduction – Topology 3
Low-cost combination that meets the performance target (SnPb(63/37), SiN-Ideal)
Cost -> 339 Peak Temp -> 130 OC
Low-cost combination that meets the performance target (SnPb(63/37), Alumina, an LTCC substrate)
Cost -> 354 Peak Temp -> 149 OC
Topology 1 -> 889, Topology 2 -> 682
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Substrate Materials for Cost Reduction – Topology 3
Silicon nitride, ideal
Alumina, an LTCC substrate
400 600 800 1000 1200 1400 1600 1800 2000115
120
125
130
135
140
145
150
155
160
165
170
Cost per IGBT Diode pair*1000 ($)
Max
imum
Tem
pera
ture
(C)
Maximum Temperature Vs Cost
Aluminum Nitride AINALN, AL-501ALN, AL-502AL-503AL-504AN75WAlumina, Al203AL203, AL-600AL2O3, AL-601AL2O3, AL-602AL203, AL-603AL2O3, AL-604AL203, AL-605AL2O3, AL-610Boron Nitride, BO-502Silicon Nitride, S1-501Silicon Nitride, IdealBeryllium Oxide (BeO)
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Topology Effect on Junction Temperature Effect of Topology on Peformance
100
105
110
115
120
125
130
135
140
0 1 2 3 4 5 6 7
Distance, mm
Tem
pera
ture
, o C
Baseline Topology 1Topology 2Topology 3
Complex interaction between spreading and convection
Direct Backside Cooling
Baseline
h = 18,350 W/(m2.K)
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Thermal Resistances – Contributions
100% 68% 61%
Opportunity for further reduction in thermal resistance through surface enhancement
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Surface EnhancementU = h . A
U = h . 3 A
U = (2.2 h) . A
Effective area would be less than 3. Let’s assume it’s about 2.2:
U = h . (2.2 A) (in the test)
(for modeling purposes)
The assumption above might be all right for a first order approximation:
Baseline, h = 18, 350 W/(m2.K)
Enhanced, h = 2.2 * h = 2.2 * 18, 350 = 40,000 W/(m2.K)
Targeted surface area enhancement is about 3
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Combined Effects of Topology and Cooling Technology on Junction Temperature
Combined Effects of Topology and Cooling Technology on Performance
100
105
110
115
120
125
130
135
140
0 1 2 3 4 5 6 7
Distance, mm
Tem
pera
ture
, o C
Baseline Topology 1, htc = 18,350Topology 2, htc = 18,350Topology 3, htc = 18,350Topology 1, htc = 40,000Topology 2, htc = 40,000Topology 3, htc = 40,000
Backside Cooling with surface enhancement
Baseline
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Conclusions and Future Studies
• Advanced thermal control (advanced cooling technologies and novel packaging topologies) helps to meet FreedomCAR program’s key target of cost.
• Direct Backside Cooling (Topology 3) has the greatest potential for cost reduction.
• Using Advanced Thermal Control, low-cost LTCC substrate (alumina) has the potential to replace the traditional, more expensive HTCC substrate, AlN.
• Surface enhancement provides further opportunity for performance enhancement .
• Future studies would involve reliability aspects and emerging substrate technologies (LTCC and Organic).
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Acknowledgements
• First author acknowledges the inputs from Andrew A. Wereszczak, Govindarajan Muralidharan (Oak Ridge National Laboratory), Rajen Chanchani (Sandia National Laboratory), Dr. Liangyu Chen (NASA Glenn Research Center) and Prof. Jean-Paul Issi.