Emerging materials for Thermal Management Al und Cu based diamond composites
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Transcript of Emerging materials for Thermal Management Al und Cu based diamond composites
Emerging materials for Thermal ManagementAl und Cu based diamond composites
L. Weber Laboratory for Mechanical Metallurgy
Ecole Polytechnique Fédérale de Lausanne (EPFL)CH-1015, Lausanne, Switzerland
EIDGENÖSSISCHE TECHNISCHE HOCHSCHULE LAUSANNE
POLITECNICO FEDERALE DI LOSANNA
SWISS FEDERAL INSTITUTE OF TECHNOLOGY LAUSANNE
ÉCOLE POLYTECHNIQUE FÉDÉRALE DE LAUSANNE
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sun set on a beachsun bath at noonlight bulb 100W
cooking plate
LD module package
Pentium 4
IGBT power moduleLD module cavity
First wall ITERsurface of the sun
heat flow density [W/cm
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equivalent black body surface temperature [K]
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The heat is on!
The heat is on!
Solution:
phase change materials
heat pipes
small active componenttransient heating
cold air flow
small active componentpermanent heating
cooling plate/circuit
spreading/absorbing the heat
large active componentpermanent heating
spreading and transfer mostly transfer
Solution:
High in plane
Medium/high through plane
Solution:
High through plane
Typical requirements on substrate or base-plate materials
• CTE similar to that of GaN and Si (3-5 ppm/K) (passive cycling) or slightly higher (active cycling).
• High thermal conductivity, [W/mK]
• High thermal diffusivity
• Sometimes: electrical conductivity
• Structural properties (stiffness, strength)
δ=λ
cp ⋅ρ
Candidate materials
Metals:
CTE too high
Ceramics:
“no” electrical conductivity, too brittle, CTE too low
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metals
ceramics
metalsceramics
area of interest
=> obvious choice:
composites
Composite concepts using carbon material
Common forms of Carbon
Continuous Carbon fibres
Chopped Carbon short-fibres
Graphite flakes
Carbon nanotubes and nanofibres
Diamond (particles and fibres)
Diamond price
Raw material prices 2007:[US$/litre]
Platinum 800’000.-Gold 380’000.-Palladium 150’000.-C-Nanotubes 12’500.-Silver 4’100.-CBN 3’000.-HC carbon fibres 2’400.-Tungsten carbide 1’300.-Tungsten 750.-Ni-Superalloys 700.-Molybdenum 680.-Titanium diboride 500.-Nickel 450.-Aluminium nitride 256.-Titanium 225.-Tin 100.-Copper 72.-Silicon carbide 50.-Alumina 40.-Aluminium 6.-
Industrial diamond price 1994 (after Ashby&Jones):
>1’000’000.- [US$/litre]
Industrial diamond price 2005:
10’000.- down to 600.- [US$/litre]
The making of diamond composites
Liquid metal infiltration process
Alternative routes:
• hot pressing of powder mixtures
• hot pressing of coated particles
Pressure infiltration apparatus
• Induction heating(using a graphite susceptor)
• primary vacuum pump (0.1 mbar)
• Crucible can be lowered on quench (directional solidification)
100 mm
• Cold wall vessel (250 bar, 200°C)Inner side of the wall in contact with a water cooled heat shield
Selected diamond grit
• Mono-crystalline diamond
• Low nitrogen level
• Relatively large size (>100µm)
Net-shape fabrication
Ag-Diamond composites
1. Pure Ag + 60 %-vol diamonds (100µm)
• Low thermal conductivity (270 W/mK)
• High coefficient of thermal expansion (≈17ppm/K)
2. Ag-Si alloy + 60 %-vol diamonds (100µm)
• High thermal conductivity (>700 W/mK)
• Low coefficient of thermal expansion (≈7ppm/K)
Cu-Diamond composites
1. Pure Cu + 60 %-vol diamonds (200µm)
• Low thermal conductivity (150 W/mK)
• High coefficient of thermal expansion (≈16ppm/K)
2. Cu-B alloy + 60 %-vol diamonds (200µm)
• High thermal conductivity (>600 W/mK)
• Low coefficient of thermal expansion (≈7ppm/K)
Matrix alloy development
• What is it that makes an alloying element an
“active” element
• How much active element do we need to get the right interface?
• And what does this quantity of active element do to the matrix properties?
Effect of active element on CTE
Active elements are needed to form carbides at the Metal/diamond (carbon) interface
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Cr concentration in Cu [at/at]
Thermal conductivity [W/mK]
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matrix thermal conductivitycomposite thermal conductivitycomposite CTE
CTE [ppm/K]
insulating inclusion
carbide stabilitylimit
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B concentration in Cu [at/at]
Thermal conductivity [W/mK]
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matrix thermal conductivitycomposite thermal conductivitycomposite CTE
CTE [ppm/K]
insulating inclusion
carbide stability limit
Ag-Si: thermal conductivity
L.Weber, Metall. Mater. Trans. 33A (2002) 1145-50
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annealing temperature [°C]
Ag-4 Si
After infiltration
Ag-Si-X: alloy requirements
The ternary alloying element X should have/generate
• “no” solubility in solid Ag
• some solubility in liquid Ag
• reduced Si-activity in the solid state
weak silicide-forming element
Ni Fe Mn
Ag-Ni binary system
• Ni content limited to 0.3-0.4 at-%
• Resistivity increase due to Ni<0.05µΩcm (after HT @ T<700°C) and is maximum about 0.4 µΩcm after HT @ 950°C.
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Ni-content [at-%]
temperature [K]Ladet (1976)
Stevenson & Wulff (1962)
this study
(Ag)
liquide
liquide + (Ni)
(Ag) + (Ni)
Ag-Ni-Si: Si activity
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xSi [-]
∆Gf [kJ/mol]
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Tokunaga (2003)
Kaufmann (1979)
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Ni3Si2
NiSi
NiSi2
Ag-Ni-Si: thermal conductivity
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∆ρ [__ ]cm
[ ]temperature KAg-2at-%SiAg-0.5SiAg-0.25SiAg-0.3Ni-0.25Si
∆ρ [µΩcm]
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temperature [K]
thermal conductivity [W/mK]
Ag-2at-%Si
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Ag-0.25Si
Ag-0.3Ni-0.25Si
measurements
Typical situation after infiltration
GPI SC
Thermal conductivity
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CTE 10-12 17-25
Kinetic effects: Al-diamond
Interface study of Al-Diamond composites
Comparison of GPI and Squeeze Casting
Influence of diamond volume fraction on CTE
Interesting CTE range can be achieved with mono-modal particle size distribution
Low pressure infiltration is possible
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volume fraction diamond [-]
bimodalmonomodal
Al-SiC
Influence of diamond volume fraction electrical conductivity
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fraction non-conducting phase [vol.-%]
normalized el. conductivity [-]
5 µm, angular12 µm, angular30 µm, angular58 µm, angular100µm, angularbimodal 3µm/30µm, angularbimodal 5µm/30µm, angularbimodal 5µm/58µm, angular bimodal 12µm/30µm, angular3-P SCS (spheroids, aspect ratio 0.275)mean-field approach (spheroids, aspect ratio 0.275)differential scheme (spheroids, aspect ratio 0.275)5 µm, acicular5µm acicular29 µm angular5 µm, slip cast
Going from 60 to 75
pct vol diamond
reduces the el.
conductivity by a
factor >2!
Importance of the interface transfer problem
Electrical conductivity: • High phase contrast• No effect of interface resistance=> no effect of phase region size and field-line distortion
Thermal conductivity: • low phase contrast=> Effect of interface resistance
Various models (extension to finite volume fractions):
Effective particle thermal conductivity:
Effective particle properties
€
d ,eff =λ d
1+λ dhbd r
=λ d
1+ B
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c = f λ m ,λ dλm
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⎠ ⎟= g λm ,
λ d ,eff
λ m,Vp
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Indirect measurement of the ITC —
size effects
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particle radius [µm]
composite conductivity [W/mK]
Exp Ag-Si/diamond
DEM; h=6.6 10^7 W/m2K
Small particles:
• Higher strength
• Better machinability
• Lower thermal cond.
• Metal diamond composites are a promising material for next generation thermal management solutions.
• They can exhibit twice the conductivity of pure silver, while having a coefficient of thermal expansion similar to semiconductor devices.
• The interface is extremely important for both, thermal conductivity and coefficient of thermal expansion.
Conclusions