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Emerging materials for Thermal Management Al und Cu based diamond composites. L. Weber Laboratory for Mechanical Metallurgy Ecole Polytechnique Fédérale de Lausanne (EPFL) CH-1015, Lausanne, Switzerland. The heat is on!. small active component transient heating. small active component

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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 MetallurgyEcole Polytechnique Fédérale de Lausanne (EPFL)

CH-1015, Lausanne, Switzerland

the heat is on

small active component

transient heating

small active component

permanent heating

large active component

permanent heating

cooling plate/circuit

cold air flow

The heat is on!

spreading and transfer

spreading/absorbing

the heat

mostly transfer

Solution:

High l in plane

Medium/high l through plane

Solution:

phase change materials

heat pipes

Solution:

High l 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, l [W/mK]
  • High thermal diffusivity
  • Sometimes: electrical conductivity
  • Structural properties (stiffness, strength)

Typical requirements on substrate or base-plate materials

candidate materials

Metals:

CTE too high

Ceramics:

“no” electrical conductivity, too brittle, CTE too low

Candidate materials

=> obvious choice:

composites

composite concepts using carbon material

Chopped Carbon short-fibres

Continuous Carbon fibres

Graphite flakes

Common forms of Carbon

Composite concepts using carbon material

Diamond (particles and fibres)

Carbon nanotubes and nanofibres

diamond price

Industrial diamond price 2005:

10’000.- down to 600.- [US$/litre]

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]

Diamond price

slide9

Liquid metal infiltration process

  • Alternative routes:
  • hot pressing of powder mixtures
  • hot pressing of coated particles
slide10

Pressure infiltration apparatus

  • Cold wall vessel (250 bar, 200°C) Inner side of the wall in contact with a water cooled heat shield
  • Induction heating (using a graphite susceptor)
  • primary vacuum pump (0.1 mbar)
  • Crucible can be lowered on quench (directional solidification)

100 mm

selected diamond grit

Mono-crystalline diamond

  • Low nitrogen level
  • Relatively large size (>100µm)

Selected diamond grit

ag diamond composites
Ag-Diamond composites
  • Pure Ag + 60 %-vol diamonds (100µm)
    • Low thermal conductivity (270 W/mK)
    • High coefficient of thermal expansion (≈17ppm/K)
  • Ag-Si alloy + 60 %-vol diamonds (100µm)
    • High thermal conductivity (>700 W/mK)
    • Low coefficient of thermal expansion (≈7ppm/K)
cu diamond composites
Cu-Diamond composites
  • Pure Cu + 60 %-vol diamonds (200µm)
    • Low thermal conductivity (150 W/mK)
    • High coefficient of thermal expansion (≈16ppm/K)
  • 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?

Matrix alloy development

effect of active element on cte
Effect of active element on CTE

Active elements are needed to form carbides at the Metal/diamond (carbon) interface

slide17

Ag-Si: thermal conductivity

After infiltration

L.Weber, Metall. Mater. Trans.33A (2002) 1145-50

slide18

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   

  

  

slide19

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.
slide20

Ag-Ni-Si: Si activity

700°C

NiSi2

NiSi

Ni3Si2

slide21

Ag-Ni-Si: thermal conductivity

∆r [µΩcm]

Typical situation after infiltration

interface study of al diamond composites comparison of gpi and squeeze casting
Interface study of Al-Diamond composites

Comparison of GPI and Squeeze Casting

influence of diamond volume fraction on cte

Al-SiC

monomodal

bimodal

  • Interesting CTE range can be achieved with mono-modal particle size distribution
  • Low pressure infiltration is possible

Influence of diamond volume fraction on CTE

influence of diamond volume fraction electrical conductivity

Going from 60 to 75 pct vol diamond reduces the el. conductivity by a factor >2!

Influence of diamond volume fraction electrical conductivity

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

Importance of the interface transfer problem

  • Thermal conductivity:
    • low phase contrast
    • => Effect of interface resistance
effective particle properties

Effective particle thermal conductivity:

Effective particle properties

Various models (extension to finite volume fractions):

indirect measurement of the itc size effects

Small particles:

  • Higher strength
  • Better machinability
  • Lower thermal cond.

Indirect measurement of the ITC —

size effects

conclusions

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