Lightweight, LowLightweight, Low--Cost Heat Cost Heat Sink for HighSink for High--Heat Flux Heat Flux

ApplicationsApplicationsArt Art FortiniFortini

ULTRAMETULTRAMETTFAWS MeetingTFAWS MeetingAugust 8, 2006August 8, 2006

Basic ConceptBasic Concept

Use openUse open--cell SiC foam as an cell SiC foam as an extended surface or cooling fin for extended surface or cooling fin for SiC integrated circuits (ICs).SiC integrated circuits (ICs).AdvantagesAdvantages•• Perfect CTE match with SiC ICsPerfect CTE match with SiC ICs•• High thermal conductivity High thermal conductivity •• High surface areaHigh surface area•• Low pressure dropLow pressure drop•• Immune to corrosionImmune to corrosion

Silicon Carbide FoamSilicon Carbide FoamHigh surface areaHigh surface areaImportant for transferring heat to cooling mediumImportant for transferring heat to cooling medium

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Surf

ace

area

(cm

2/cm

3)

100 ppi

80 ppi65 ppi

Pressure DropPressure Drop

Silicon carbide Silicon carbide foamfoam•• 0.5 x 2 x 30.5 x 2 x 3”” slabslab•• Water flow parallel Water flow parallel

to long axis.to long axis.•• Important for Important for

flowing large flowing large quantities of quantities of coolant without coolant without pressure drop pressure drop penalty.penalty.

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flow (g/min)

dP (m

m H

2O)

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flow (cm/s)

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sid)

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80, 20

no foam

Pressure DropPressure Drop

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air velocity (ft/s)

pres

sure

dro

p (p

sid) 20

30456580100

1" thick foam • Carbon foam– 1” thick slab– Air flow

perpendicular to thickness

– Very low pressure drop

UltrafoamsUltrafoams

Begin with polyurethaneBegin with polyurethaneImpregnate with resinImpregnate with resinPyrolyze to form glassy carbonPyrolyze to form glassy carbon•• 33--1000 pores per inch (ppi)1000 pores per inch (ppi)

CVI with SiCCVI with SiC•• 55--30% relative density30% relative density•• Other materials: Si, Gr, pyC, Si(C), Other materials: Si, Gr, pyC, Si(C),

refractory metals, etcrefractory metals, etc

UltrafoamUltrafoam

Vitreous carbon Silicon carbide

Basic ConceptBasic Concept

FaceplateIC heatsource

Coolant in Coolant out

SiC foam

ExperimentalExperimental

Copper block w/ resistive heaters

SiC foamTi Pi

Te

dP

Thermocouple (at heater/foam bondline) Insulation

Coolant outletCoolant inlet

Bondline

Unique Thermal Control Challenges(High Heat Flux, High Power, Low Temperature)

10 3

4 10

2 10

1 10

10 0

10 -1

10 -2

1000 2000 3000 4000 5000

Solar heating

Rocket motor case (external)

Reentry from Earth orbit

Nuclear blast (1 Mt, 1 mi)

Ballistic entry Rocket nozzle throat (internal)

Laser diodes

Temperature (K)

2 q" W/cm

Electronic & microwave devicesLaser diodesLaser gain media

150°C

•Phase II goal was to reach 1000 W/cm2 with temperature below 150°C

Experimental ResultsExperimental ResultsFoam PPI / density Heat Flux Flow Rate Heat Flux / Flow Rate

Cooler SurfaceTemperature

(W/cm2) (GPM) (W min /cm2 G) (°C)100ppi/ 9.8% 711 0.5 1422 1131000ppi / 12% 867 0.5 1734 122100ppi/ 10% 612 0.5 1224 47.81000ppi/ 5% 1006 0.64 1572 165300ppi/ 20% 1011 0.5 2022 53100ppi/ 20% 1000 1.0 1000 135300ppi/ 20% 758 0.3 2527 42.4

• Phase II goal: 1000 W/cm2 while below 150°C.

• Ultramet SiC foam 1011 W/cm2 at only 53°C!

Experimental ResultsExperimental Results

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Heat Flux (W/cm2)

Coo

ler S

urfa

ce T

empe

ratu

re (C

)

300ppi 2-28-06

300ppi with Cu Flap

600ppi-copper flap 9-14-051000ppi (2)(9-9-05)

100PPI-10%

100ppi-20%

100-20%

300ppi-20%

600ppi

Experimental ResultsExperimental ResultsHeat Stress = Heat Flux/ Flow rate (Gallons per minute)

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Heat Stress (W*min/cm2*G)

Coo

ler S

urfa

ce T

empe

ratu

re (C

)

300ppi 2-28-06

300ppi with Cu flap

600ppi-copper flap 9-14-051000(2)(9-9-05)

100PPI-10%

100ppi-20%

100-20%

300ppi-20%

600ppi

Thermal ModelingThermal ModelingX-Ray Tomography Ultramet SiC Foam

Thermal Model InputThermal Model InputPartPart Side DimensionsSide Dimensions ThicknessThickness Thermal Conductivity Thermal Conductivity

(W/m C)(W/m C)

SiC FoamSiC Foam 2 x 22 x 2”” 0.50.5”” 4040

TIM1TIM1 2 x 22 x 2”” 100 100 µµmm 4040

SiC Heat spreaderSiC Heat spreader 2 x 22 x 2”” 250 250 µµmm 200200--500 (4H500 (4H--SiC)SiC)

Die Attach (TIM2)Die Attach (TIM2) 5 x 5 mm5 x 5 mm 50 50 µµmm 4040

DieDie 5 x 5 mm5 x 5 mm 380 380 µµmm 200200--500 (4H500 (4H--SiC)SiC)

GaN active areaGaN active area 0.25 x 4 mm0.25 x 4 mm n/an/a n/an/a

Modeling ConclusionsModeling Conclusions1kW/cm2 with Heat Spreader

0.1 and 0.5 GPM 27 and 28 °C

1kW/cm2 without Heat Spreader

0.1 and 0.5 GPM 61 and 48 °C

0.1 GPM 0.1 GPM

0.5 GPM0.5 GPM

Other WorkOther Work-- High Heat Flux GaN-Based RF Componentsand Cooling Methods

Jeff Calame, Steve Binari, Robert Myers †, and Frank Wood †Naval Research Laboratory, Washington, DC 20375

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Measured power density (W/cm2 )

Experimentally measured temperatures(Cooler surface under heat probe source center )

(0.502 gal/min, 20 oC H2O inlet)

OFHC copper cooler

Silicon cooler

Aluminumnitridecooler

Tem

pera

ture

( o C

)

-Micromachined to 500µm

3rd Annual Workshop on Thermal Management of High Flux Commercial and Military Electronics University of Maryland, College Park, MD October 18, 2004

Ultramet Foam (same flow rate)

•Ultramet SiC foam has comparable performance to micromachined OFHC copper and single crystal silicon with diamond heat spreader.

SummarySummaryEffects of SiC foam:Effects of SiC foam:•• 1011 W/cm1011 W/cm2 @53C w/ 0.5 GPM water@53C w/ 0.5 GPM water

Thermal Model predicts improvements Thermal Model predicts improvements by going to heat spreader configuration.by going to heat spreader configuration.•• 27 27 ººC with heat spreader w/ 0.1 GPMC with heat spreader w/ 0.1 GPM•• 61 61 ººC for 100ppi. 10% density (stock item) C for 100ppi. 10% density (stock item)

at low flow rate.at low flow rate.

Excellent heat transfer Excellent heat transfer little material little material is requiredis required (small volume/ light and (small volume/ light and inexpensive).inexpensive).Low coolant flow rates requires less in Low coolant flow rates requires less in way of supporting systemsway of supporting systems-- pumping, pumping, filtration, etc.filtration, etc.