EIDGENГ–SSISCHE TECHNISCHE HOCHSCHULE LAUSANNE POLITECNICO FEDERALE DI LOSANNA SWISS FEDERAL INSTITUTE OF TECHNOLOGY LAUSANNE Г‰COLE POLYTECHNIQUE FГ‰DГ‰RALE DE LAUSANNE Emerging materials for Thermal Management Al und Cu based diamond composites L. Weber Laboratory for Mechanical Metallurgy Ecole Polytechnique FГ©dГ©rale de Lausanne (EPFL) CH-1015, Lausanne, Switzerland T rf e rs P of th e lI vi 4 su n R ty e TE ca e e m ul t iu od al e tw ul m en ag at 0W pl 10 ck g pa er od ac Fi m w e in lb h on ac no be at a bu th n ok ul po od LD B m su IG LD ht ba to co lig n se su n h ea t flo w d e ns ity [W /cm 2 ] 10000 6480 1000 3640 100 2050 10 1152 1 648 0.1 364 0.01 205 e q u iv a le n t b la c k b o d y s u rfa c e te m p e ra tu re [K ] su The heat is on! The heat is on! small active component transient heating small active component permanent heating cold air flow spreading/absorbing the heat spreading and transfer large active component permanent heating cooling plate/circuit mostly transfer Solution: Solution: Solution: phase change materials High l in plane High l through plane heat pipes Medium/high l through plane Typical requirements on substrate or baseplate 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] пЃ¤ пЂЅ • High thermal diffusivity • Sometimes: electrical conductivity • Structural properties (stiffness, strength) l cp пѓ— пЃІ Candidate materials Metals: CTE too high Ceramics: “no” electrical conductivity, too brittle, CTE too low => obvious choice: composites Composite concepts using carbon material Chopped Carbon short-fibres Continuous Carbon fibres Graphite flakes Common forms of Carbon Carbon nanotubes and nanofibres Diamond (particles and fibres) Diamond price Raw material prices 2007: [US$/litre] Platinum Gold Palladium C-Nanotubes Silver CBN HC carbon fibres Tungsten carbide Tungsten Ni-Superalloys Molybdenum Titanium diboride Nickel Aluminium nitride Titanium Tin Copper Silicon carbide Alumina Aluminium 800’000.380’000.150’000.12’500.4’100.3’000.2’400.1’300.750.700.680.500.450.256.225.100.72.50.40.6.- Industrial diamond price 1994 (after Ashby&Jones): >1’000’000.- [US$/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 • Cold wall vessel (250 bar, 200В°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) 100 mm • Crucible can be lowered on quench (directional solidification) Selected diamond grit • Mono-crystalline diamond • Low nitrogen level • Relatively large size (>100Вµm) Net-shape fabrication Ag-Diamond composites 1. Pure Ag + 60 %-vol diamonds (100Вµm) • Low thermal conductivity (270 W/mK) • High coefficient of thermal expansion (≈17ppm/K) 2. Ag-Si alloy + 60 %-vol diamonds (100Вµm) • High thermal conductivity (>700 W/mK) • Low coefficient of thermal expansion (≈7ppm/K) Cu-Diamond composites 1. Pure Cu + 60 %-vol diamonds (200Вµm) • Low thermal conductivity (150 W/mK) • High coefficient of thermal expansion (≈16ppm/K) 2. Cu-B alloy + 60 %-vol diamonds (200Вµm) • 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 Ag-Si: thermal conductivity After infiltration L.Weber, Metall. Mater. Trans. 33A (2002) 1145-50 Ag-Si-X: alloy requirements The ternary alloying element X should have/generate • “no” solubility in solid Ag Ni пЂґ Fe пЂґ Mn пЂё • some solubility in liquid Ag пЂґ пЂё пЂґ • reduced Si-activity in the solid state пЂґ пЂґ пЂґ пѓњ weak silicide-forming element Ag-Ni binary system 1400 • Ni content limited to 0.3-0.4 at-% • Resistivity increase due to Ni<0.05µΩcm (after HT @ T<700В°C) and is maximum about 0.4 µΩcm after HT @ 950В°C. liquide te m per a tur e [K ] 1300 liquide + (Ni) 1200 (Ag) 1100 (Ag) + (Ni) 1000 Ladet (1976) 900 Stevenson & Wulff (1962) this study 800 0 0.2 0.4 0.6 Ni-content [at-%] 0.8 1 Ag-Ni-Si: Si activity 700В°C 0 Acker (1999) Tokunaga (2003) -10 -20 NiSi2 -30 NiSi ВІG f [kJ /m o l] Kaufmann (1979) Ni3Si2 -40 -50 -60 0 0.2 0.4 0.6 x Si [-] 0.8 1 Ag-Ni-Si: thermal conductivity 450 1200 400 th erm al con d u ctivity [W /m K ] te m per a tur e [K ] 1100 1000 900 800 Ag-2at-%Si Ag-0.5Si Ag-0.25Si 700 350 300 250 200 150 Ag-2at-%Si Ag-0.5Si 100 Ag-0.25Si Ag-0.3Ni-0.25Si Ag-0.3Ni-0.25Si 50 measurements 0 600 0 1 2 3 пЃІ [__cm] ∆ ВІ[µΩcm] 4 5 700 800 900 1000 temperature [K] Typical situation after infiltration 1100 Kinetic effects: Al-diamond Thermal conductivity CTE GPI SC 660 110 10-12 17-25 Interface study of Al-Diamond composites Comparison of GPI and Squeeze Casting Influence of diamond volume fraction on CTE Al-SiC Interesting CTE range can be achieved with mono-modal particle size distribution пѓћLow pressure infiltration is possible monomodal bimodal Influence of diamond volume fraction electrical conductivity 0.5 Going from 60 to 75 0.45 pct vol diamond n o rm a liz e d e l. c o n d u c tiv ity [-] 0.4 reduces the el. 0.35 conductivity by a 0.3 factor >2! 0.25 0.2 5 Вµm, angular 12 Вµm, angular 30 Вµm, angular 58 Вµm, angular 100Вµm, angular bimodal 3Вµm/30Вµm, angular bimodal 5Вµm/30Вµm, angular bimodal 5Вµm/58Вµm, angular bimodal 12Вµm/30Вµm, angular 3-P SCS (spheroids, aspect ratio 0.275) mean-field approach (spheroids, aspect ratio 0.275) differential scheme (spheroids, aspect ratio 0.275) 5 Вµm, acicular 5Вµm acicular 29 Вµm angular 5 Вµm, slip cast 0.15 0.1 0.05 0 35 40 45 50 55 60 fraction non-conducting phase [vol.-%] 65 70 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 Effective particle properties Effective particle thermal conductivity: l d ,eff пЂЅ 1пЂ« ld ld пЂЅ ld 1пЂ« B h bd r Various models (extension to finite volume fractions): пѓ¦пЂ пѓ¶пЂ пѓ¦пЂ пѓ¶пЂ l d ,eff ld l c пЂЅ f пѓ§пЂ l m , , h bd , r,V p пѓ·пЂ пЂЅ gпѓ§пЂ l m , ,V p пѓ·пЂ lm lm пѓЁпЂ пѓёпЂ пѓЁпЂ пѓёпЂ Indirect measurement of the ITC — size effects Small particles: 1000 co m po site con du ctivity [W /m K ] 900 • Higher strength 800 700 • Better machinability 600 500 • Lower thermal cond. 400 300 Exp Ag-Si/diamond 200 DEM; h=6.6 10^7 W/m2K 100 0 0 20 40 particle radius [ 60 80 Вµ m] 100 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.
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