-MRS-
Chairs
Michael Cima Subhash Shinde, MIT IBM Microelectronics
* Invited paper
SESSION LL1: THERMAL CONDUCTIVITY MECHANISMS AND MEASUREMENT
Chairs: Michael J. Cima and Subhash L. Shinde
Monday Morning, December 1, 1997
Boston College (M)
9:00 AM *LL1.1
CVD DIAMOND: AN ENABLING MATERIAL FOR THERMAL MANAGEMENT. J. Yehoda, Diamonex, Allentown, PA.
Abstract Not Available
9:30 AM LL1.2
ELASTIC AND INELASTIC ELECTRON SCATTERING IN DIAMOND. David C. Bell, Centre for Materials Science and Engineering, MIT, Cambridge, MA.
The physical properties of diamond are some of the most interesting of natural materials. Electron energy-loss spectroscopy studies of a single crystal diamond wedge allow some of the basic electron matter interactions to be studied. The electron energy-loss spectrum has been examined with particular reference to the plasmon excitations in the crystal. The mean-free path of the electrons through the diamond crystal and the nature of the observed features in the energy-loss spectrum have been examined. The low energy-loss region of the electron energy-loss spectrum revealed features, notably the plasmon at 33 eV and an interband transition 1,2 at 23 eV. The plasmon intensity variation was observed to vary with crystal thickness. This variation was used to calculate the mean-free path for 400 KeV electrons in the diamond wedge, and was determined to be 900 ‰ ± 400 ‰. This value compares favorably with computed values. The VG HB603-MIT STEM, equipped with a PEELS, was modified to produce energy filtered images and line-scans of the plasmon intensity variation with thickness. Differences between elastic and multiple inelastic scattering were observed with adjustment of the electron energy-loss filter. A zero eV offset allowed the zero energy-loss or elastic scattered image to be observed. Offset changes were then made to follow inelastic scattering processes through the thickness variations in the wedge.
9:45 AM LL1.4
THERMAL CONDUCTIVITY OF TETRAHEDRAL AMORPHOUS CARBON (TAC) FILM PREPARED BY FILTERED CATHODIC VACUUM ARC TECHNIQUE. George Chena, Ping Huib, aAvimo Group Limited, SINGAPORE, or Photonics Lab, School of EEE, Nanyang Technological University, SINGAPORE; bSchool of EEE, Technological University, SINGAPORE.
Tetrahedral amorphous carbon (TAC) coating combines many unique properties such as extreme hardness, chemical inertness and high electrical resistivity, has been an interesting research topic recently.1 In Nanyang Technological University, the TAC film is produced using the Filtered Cathodic Vacuum Arc technique. EELS measurement showed that a sp3 fraction of 87.5% was achieved. 2 As the miniature of electronics components in integrated electronics relies on fast heat dissipation, high thermal transport material uses a heat sink or packaging is sought after. This investigation of the thermal properties of the TAC film could lead to potential application in electronics industry. In our measurement, pulsed photothermal reflection technique is employed. The advantage of this technique is that it is a non-contact method and requires little sample preparation.3 In our experiment, Nd YAG pulse at 532nm of 8 nsec is applied on the sample, metallized TAC on silicon. The surface temperature of the sample rises sharply upon receiving the pulse, and then relaxes with time. This relaxation rate is depended on the thermal diffusivity of the underlying materials. In order to obtain this transient phenomenon, a continuous HeNe laser monitors the change in reflectivity of the surface. Since the reflectivity and temperature has an inverse linear relationship,4 the relaxation temperatures profile can be obtained by capturing the change in the reflectivity. To obtain the thermal diffusivity of the TAC film, mathematical models are developed to fit the unknown parameters with the captured temperature profile. Two mathematical models, a two-layer system with the film treated as a thermal resistance and a three-layer model, are considered in the analysis. With the thermal diffusivity value being extracted, thermal conductivity can be calculated using the measured film density and known bulk value of specific heat.5 This calculated value would be compared with other groups results.
10:30 AM *LL1.5
THERMAL PROPERTY STUDIES OF HIGH THERMAL CONDUCTIVITY , FIBER-REINFORCED COMPOSITE MATERIALS BY THE LASERFLASH TECHNIQUE. R.C. Campbell, S.E. Smith, Holometrix, Inc., Bedford, MA.
The success of efforts to enhance the thermal conductivities of materials used in microelectronics applications often depends on precise control of microstructure. Measurement of thermal diffusivity by the laserflash method has proven to be an effective means of probing microstructure, and thus of evaluating the processes and materials used in such development programs. As discussed in this paper, application of this technique to composite materials with high conductivity fiber reinforcements presents special challenges, particularly in designs involving oriented, continuous fibers in a low conductivity matrix. Thermal diffusivity and conductivity results are presented for a variety of composites, including some with high-modulus graphite fibers in a resin matrix that exhibit highly anisotropic properties. The degree of anisotropy is measured in graphite/epoxies by modifying the schemes for heat pulse input and detection, to produce heat flow along any one of the principle axis directions. Also presented is a technique for analyzing heat pulse data to determine, simultaneously, specific heat as well as thermal diffusivity for the same specimen, allowing immediate calculation of thermal conductivity during the test run; conductivity values thus obtained are compared with results from steady state tests.
11:00 AM LL1.6
THERMAL CONDUCTIVITY MEASUREMENTS OF DIAMOND FILMS. Arthur J. McGinnis, K. Jagannadham, Department of Materials Science and Engineering, North Carolina State University, Raleigh, NC; Hain Wang and R.B. Dinwiddie, Metals and Ceramics Division, Oak Ridge National Laboratory, Oak Ridge, NC.
Thermal conductivity measurements are performed on single and multilayer diamond coatings on silicon and aluminum nitride. These measurements are used to understand the significance of thermal resistance associated with interfacial layers between diamond and aluminum nitride. Heat spreader characteristics of single and multilayer diamond substrates and their use in electronic packaging are described from results of IR imaging and thermal conductivity measurements.
11:15 AM LL1.7
THERMAL DIFFUSIVITY MEASUREMENTS USING AN INPROVED AC-CALORIMETRIC TECHNIQUE. R.P. Tye, R. Kato, Sinku Riko Inc., Yokohama, JAPAN.
High thermal conductivity materials, both individually and in combination with other materials, are used in a broad range of applications over a wide temperature range, especially in electronics components. Some new materials are available only in very limited sizes and configurations while others are used in the form of thin films and wafers having thermal properties that differ from those of the bulk material. These issues require that thermal properties be measured on the particular form and under the conditions in which it is applied thus requiring the use of newer measurement methods than those that have been used conventionally. This paper describes an improved form of modified ac-calorimetry (Angstrom method) using a scanning laser as the energy source. This can be used to measure the thermal diffusivity and derived thermal conductivity of a very broad range of materials in thicknesses varying from a micron to a millimeter or so. The performance will be illustrated with the results of measurements on a range of high thermal conductivity ceramic, metal, and CVD diamond materials. The potential for its use to examine effects of grain boundaries, defects, etc., will also be illustrated and discussed. Mention will also be made of the application of Scanning Thermal Microscopy as a new method for similar studies at the microscopic level.
11:30 AM LL1.8
THERMAL CONDUCTIVITY OF COMPOSITE CUPRATE CERAMICS. M. Ausloos, H. Bougrine, S. Dorbolo, M. Houssa, and M. Pekala (*), S.U.P.R.A.S., Institut de Physique, Université de Liège, Liège, BELGIUM; (*) also at Departement of Chemistry, University of Warsaw, Warszawa, POLAND.
Thermal conductivity of superconducting cuprate ceramics probe several scattering mechanisms and dissipation processes. We have calculated and measured the thermal conductivity of such high-Tc superconductors using the variational method described by Ziman, in order to explain the different behaviors in various materials, like differences in the pronounced maximum observed below the critical temperature Tc,and the behavior at high temperature. We have considered the influence of the dimensionality and the interlayer coupling energy. The thermal conductivity has been investigated in presence or not of a magnetic field. We have considered elastic scattering of electrons by impurities as well as elastic and inelastic scattering of electrons by acoustic phonons and phenomenologically taken into account the scattering by grain boundaries, dislocations, pores, and sheet-like faults1. We have neglegted the scattering of electrons by high frequency optical phonons. The region below the critical temperature has received much attention. We show that measurements of the thermal conductivity of such materials can sometimes lead to some structure at intermediate temperature, sometimes showing a double peak, an extrinsic structure, depending on the experimental set-up.
11:45 AM LL1.9
TEM ANALYSIS OF THE GRAIN BOUNDARY STRUCTURE FOR CVD -SiC. K. Tanaka, M. Kohyama and M. Iwasa, Osaka National Research Institute, Ikeda, JAPAN.
Silicon carbide is a technologically important material widely known for its good thermomechanical properties. Yet, its powders are very difficult to sinter without the help of additives, and grain boundaries can often contain a second phase whose presence is detrimental to the performance of the material. However, chemical vapor deposition (CVD) techniques can easily provide dense materials of high purity, and interfaces that are well defined even n covalent materials. Moreover, CVD specimens often exhibit preferential orientation during growth, and this enhances the probability of coincident grain boundary formation. It is important to know the grain boundary structure to understand the fundamentals of thermal-conductivity. Conventional and hi high-resolution TEM analysis were performed on CVD -SiC with a preferential orientation of (220), and grain size of approximately l0m. Most of the grams contained many stacking faults and twin boundaries due mainly to the CVD technique. The majority of grain boundaries were =3 coherent twins lying on a (111) plane, showing a sharp and well defined contrast. Twins were often very thin, usually only a few atomic layers thick. Coherent and incoherent =3, 9 and 27 boundaries were investigated and their atomic structures were determined. Chemical composition and electronic states at the grain boundaries were also studied. The relationship between grain boundary structure and thermal-conductivity has been discussed.
SESSION LL2: PROCESSING AND METALLIZATION
Chairs: Arne Knudsen and Subhash L. Shinde
Monday Afternoon, December 1, 1997
Boston College (M)
1:30 PM *LL2.1
INTERRELATIONSHIPS BETWEEN ALUMINUM NITRIDE POWDER PROPERTIES AND SINTERED BODY PERFORMANCE. Teresa Kotanchek, Lynne Mills, Junhong Zhao, The Dow Chemical Company, Midland, MI.
Currently, aluminum nitride is utilized in a limited, but growing number of commercial electronic applications. Most AlN ceramics are marketed either as thick- or thin-film substrates or as cofired structures, with typical thermal conductivity values averaging 170 W/m-K. Because of its excellent coefficient of thermal expansion match to silicon, AlN is also a leading candidate for large-area and multi-chip substrates. The utility of aluminum nitride is fundamentally based on its high inherent thermal conductivity and sinterability. The primary powder features which impact densification and performance include chemical purity, both surface and bulk, and particle morphology, size and distribution. Many of these powder attributes are dependent upon the synthesis method employed. For example, most commercial powders, produced either by carbothermal reduction or direct nitridation, exhibit distinct characteristics. These differences impact powder stability, sintering aid demand, green forming and consolidation. Management of oxygen in the raw powder, during consolidation, and in any postprocessing is critical to successful manufacture of fully dense, high thermal conductivity components. The role of other impurities can be equally important. In this presentation, we will review the interrelationship of these powder characteristics on process stability, sinterability and sintered body performance.
2:00 PM *LL2.2
A COMPARISON OF POTENTIAL SUBSTRATES FOR GALLIUM NITRIDE EPITAXY. J. H. Edgar, Kansas State University, Dept of Chemical Engineering, Manhattan, KS.
In this paper, a comparison is made of the advantages and disadvantages of the more than one dozen different substrates (including sapphire, silicon carbide and spinel) successfully employed for gallium nitride heteroepitaxy. Because bulk GaN substrates are not commercially available, researchers have been forced to use heteroepitaxy in their pursuit of GaN based blue and green laser diodes. Potential substrates are compared in terms of their thermal (thermal conductivity, thermal expansion coefficients, and thermal stability), mechanical (hardness and modulus), crystalline (crystal orientation, polarity, and lattice constant mismatch), electrical, and chemical properties. High thermal conductivity substrates are preferred for their ability to dissipate heat during device operation. Electrically conductive substrates enable the elimination of front side device contacts. To date, a small lattice constant mismatch has not been essential for producing the best GaN thin films, as evidenced by the high crystal quality of GaN epitaxially grown on sapphire substrates. The substrate must be able to withstand temperatures in excess of 850C, and must not lose its ability to support epitaxy in a reactive nitrogen environment.
3:00 PM LL2.3
STUDIES ON METALLIZATION OF CVD DIAMOND SUBSTRATES FOR ELECTRONICS PACKAGING*. E.S.K. Menon, I. Dutta and D.E. Kroll, Department of Mechanical Engineering, Naval Postgraduate School, Monterey, CA.
CVD diamond offers substantial advantages over ceramics as a packaging material because of its excellent thermal conductivity. However, conventional metallizaton approaches are not suitable for CVD diamond substrates since they produce poorly adhesive interconnects. In this presentation, a novel approach for producing adherent metallizations on CVD diamond will be discussed. In this technique, a very thin, nanocrystalline layer of alumina is produced on the CVD diamond substrate by using a suitable inter-layer. Because of its thinness, the layer is not expected to result in significant degradation of the thermal properties of the substrate, while helping reduce interfacial stresses. The major advantage of this approach is that it obviates the need for patterning the adhesion-enhancing inter-layer, which is usually metallic, between the final metallization and CVD diamond. Subsequent metallization of these substrates were carried out using Ag based FERRO 3350 and Au based DuPont 101 (modified). Results of SEM, SAM and TEM studies of the metallization produced via this technique will be discussed.
3:15 PM LL2.4
WxSiy METALLIZATION OF AlN SUBSTRATES FOR HIGH TEMPERATURE MICROELECTRONICS. M. Qian1, C. Toy2, E. Savrun2, and M. Sarikaya1; 1University of Washington, Seattle, WA, 2Sienna Technologies, Inc., Woodinville, WA.
Sic integrated circuits (ICs) are candidates for high temperature (T>600C) applications. Packaging and metallization materials are needed to incorporate SiC ICs into electronic devices. AIN is uniquely qualified as a substrate and packaging material due to its high thermal conductivity, and chemical and thermomechanical compatibility with SiC at high temperatures. The current ambient-temperature metallization materials, however, cannot meet the performance requirements imposed upon by the high temperature environment. We have investigated Wx Siy as a possible metallization material with AIN for SiC ICs. WxSiy thin films were co-sputtered using Si and W targets on AIN substrates followed by high temperature heat treatments under various atmospheric conditions. The samples were then characterized in terms of their interface mechanical, electrical, chemical, and structural stability. Pull tests indicated excellent adhesion of the film to the substrate, while the sheet resistance indicated better than acceptable values. As deposited and heat-treated samples were structurally characterized using AFM and TEM f techniques, including EELS, to evaluate thin-film evolution and interface characteristics The results of WxSiy metallization are discussed with implications of AIN as a strong candidate substrate for SiC in high temperature applications.
3:30 PM LL2.5
SELECTIVE SUBSTRATE METALLIZATION PROCESS FOR ALUMINUM NITRIDE. Lynne M. Svedberg, Kenneth C. Arndt, Michael J. Cima, Massachusetts Institute of Technology, Cambridge, MA.
Advances in hybrid microelectronics demand the development of high performance packaging materials and components. Three-dimensional multichip modules and wireless applications require increased heat dissipation in all directions and reduction of thermal mismatch concerns. Aluminum nitride is a promising material for these and other high power applications. It has a thermal conductivity almost 10 times that of alumina, dissipates heat through natural convective cooling, and has a coefficient of thermal expansion close to that of silicon. AlN, unlike alumina, is hydrolytically reactive and corrodes rapidly at high pH. The reactivity of AlN in aqueous solutions becomes a problem for post-sintering metallization processes. Commercially used electroless gold baths have a pH around 14. Other options for selectively plating AlN, such as a lower pH electrolytic plating baths with removable interconnects and/or coatings on ceramic surfaces which are resistant to the plating bath, are expensive and labor intensive. This paper will present a novel gold metallization process which deposits gold only on desired features and eliminates contact between the corrosive medium and the AlN surface. This process may be used for metallizing electrically isolated regions and reworking defectively plated packages. The chemistry, processing parameters, and manufacturing potential of this selective substrate metallization process will be discussed.
3:45 PM LL2.6
METALLIZING ALUMINUM NITRIDE SUBSTRATE BY USING PULSE HIGH ENERGY DENSITY PLASMA GUN. Xiang-Jun He, Bing Li, Chi-zi Liu, Yu-Feng Li and Si-Ze Yang, Group 101, Inst of Physics, Chinese Academy of Sciences, Beijing, CHINA.
Ti films metallization of AlN substrate was performed by using pulse high energy density plasma (PHEDP) gun. The surface morphology of PHEDP Ti films was observed by using scanning electron microscope (SEM) and PHEDP induced interface reactions of Ti films with AlN substrate were investigated by x-ray diffraction (XRD). To characterize the reactions occurring at the interface, thermally induced and medium energy argon ion beam induced interface reactions were also investigated as comparison. PHEDP Ti films consisted of closely packed great grains and the lower voltage is good for the formation of a smooth surface. PHEDP remarkably promotes the interfacial reactions of Ti with AlN, and TiN was detected at the interface for the sample prepared with 1kV applied gun voltage. TiN, TiAl3 and TiAl phases were formed for the samples with 2-4 kV applied gun voltage.
4:00 PM LL2.7
NOVEL, LOW-COST INTERGRATED SUBSTRATES FOR POWER ELECTRONICS. W. Kowbel, and J.C. Withers, MER Corp., Tucson, AZ; and W.L. Vaughn, NASA LARC.
Rapid advances in high power electronic packaging require the development of new heatsink/substrate materials. Advanced composites designed to provide thermal control as well as improved thermal conductivity have the potential to provide benefits in the removal of excess heat from electronic devices. Carbon-carbon (C-C) composites are under considerations for numerous electronic packaging applications. The very high cost (up to $10,000/lb) of C-C composites has hindered their wide spread commercialization. A new manufacturing process has been developed to produce high thermal conductivity (400W/mK) C-C composite at greatly reduced cost (less than $50/lb). Several types of, such as CVD AIN, CVD Si and polymer slurry based low dielectric coating were applied to the C-C composite. Processing schemes were developed to produce crack-face coatings. Metallization of the dielectric coating was performed for the process integration with electronic devices. Thus, integrated substrates for power electronics were fabricated without the need of conventional metal/ceramic joining and associated high stresses. The properties of this new composite material for power electronics substrates will be presented.
SESSION LL3: COMPOSITES - PROCESSING AND PROPERTIES
Chairs: Michael J. Cima and Teresa Guiton Kotanchek
Tuesday Morning, December 2, 1997
Boston College (M)
8:30 AM *LL3.1
HIGH PERFORMANCE PLASTIC PACKAGINGArne Knudsen, Dow Chemical Company, Midland, MI.
Abstract Not Available
9:00 AM LL3.2
HIGH THERMAL CONDUCTIVITY CARBON-CARBON COMPOSITES FOR THERMAL MANAGEMENT APPLICATIONS. I. Golecki and L. Xue, AlliedSignal, Inc., Morristown, NJ; R. Leung, AlliedSignal Advanced Microelectronic Materials, Sunnyvale, CA; T. Walker, Allied Signal Aircraft Landing Systems, South Bend, IN.
Carbon (fiber) - Carbon (matrix) composites have the highest thermal conductivity per unit density among materials suitable for thermal management applications. C-C composites also have high toughness and their mechanical strength increases with temperature. We have developed C-C materials and structures for heat management applications at elevated temperatures, using pitch-based fiber preforms. Densities of 2.0-2.2 g/cm3, in-plane thermal conductivity of 590 W/m.K and tensile strength of 400 MPa have been measured in thin panels. Structures suitable for thermal management aerospace applications have been fabricated.
9:15 AM LL3.3
HIGH-THERMAL-CONDUCTIVITY SILICON NITRIDE CERAMICS. Naoto Hirosaki, Yusuke Okamoto, Motohide Ando, Fumio Munakata, Yoshio Akimune, Nissan Motor Co, Ltd, Mat Res Lab, Yokosuka, JAPAN.
Thermal conductivity of self-reinforced silicon nitride was improved by promoting grain growth and selecting a suitable additive system in terms of composition and amount. Beta-Si3N4 doped with Y2O3-Nd2O3 (YN) or Y2O3-Al2O3 (YA) was gas-pressure sintered at 1700 to 2200C. The effects of additive composition, amount, and sintering conditions on the thermal conductivity were investigated in relation to the grain growth and microstructure. Higher temperature promoted grain growth and increased the thermal conductivity in YN system. On the other hand, with YA, thermal conductivity considerably decreased with a lager additive amount because the Al and O dissolved into Si3N4 grains to form a sialon solid solution. The key processing parameters for high thermal conductivity of silicon nitride were the sintering temperature and additive composition. Thermal conductivity of 128 W/(mK) was produced; this value was about twice as high as previous reported value.
9:30 AM LL3.4
AQUEOUS SOL-GEL MODIFICATION OF THE FIBER-MATRIX INTERFACE IN GRAPHITE FIBER ALUMINUM MATRIX COMPOSITES. Araldina C. Geiculescu, Dept of Chemistry, H.Garth Spencer, Dept of Chemistry, Henry J. Rack, Dept of Ceramics and Materials Engineering, Clemson Univ, SC, and Brian J. Sullivan, Materials Research and Design, Inc., Rosemont, PA.
Graphite fibers with thermal conductivities approaching 1kW/mK have become available for inclusion in high thermal conductivity composites. However, inclusion of these fibers in aluminum metal matrix composites requires that they be coated to prevent reaction between the graphite fiber and the aluminum matrix during composite fabrication. Preliminary calculations suggest that this may be accomplished without seriously degrading the thermal conductivity of the final composite through incorporation of a thin oxide barrier layer between the graphite fiber and the aluminum matrix. Previous experience by the authors has shown that a coating of this type can be applied to graphite fibers through sol-gel coating using titanium isopropoxide in an alcohol solvent anf that the coated fibers can be cast in an aluminum MMC composite by pressure infiltration. Unfortunately, the TiO2 coating derived from this procedure undergoes a phase transformation at approximately 700 C thereby limiting its utility in aluminum MMC fabrication where liquid metal temperatures can easily exceed this temperature. The formation of zirconia thin-film caoatings offers a possible solution to this problem. This paper presents an investigation of the formation of zirconia thin film coatings on graphite fibers by aqueous sol-gel procedures. The aqueous sol-gel coating procedure includes three steps:(1)dip-coating the fiber tow with a dilute zirconium acetate coating solution, (2)removing the volatile components to form a gel coating, and (3)developing a crystalline coating by heating through a programmed temperature regimen in a controlled environment. Continuous, crack-free, bridge-free coatings of zirconia on the circular graphite fibers 10 m in diameter coated as tows have been obtained by this procedure without the requirement for tow spreading. Conditions for obtaining 100 nm thick coatings on unsized, sized and size-removed fibers and their effects on coating uniformity and performance will be discussed.
10:15 AM LL3.5
LOW-COST, HIGH THERMAL CONDUCTIVITY SiC-SIC COMPOSITES. W. Kowbel, and I.C. Withers, MER Corp., Tucson, AZ.; and G.E. Youngblood, PNNL.
SiC-SiC composites offer excellent potential for numerous commercial applications including thermal management. Very high manufacturing cost ($5,000/lb) and very low through-the-thickness thermal conductivity, greatly hinders their commercial applications. A new chemical vapor reaction (CVR) process was applied to produce pure -SiC/-SiC composites. The projected cost is greatly reduced as composed to the state-of-the-art CVI-SiC composites ($200/lb vs $3,000/lb). In addition, a breakthrough is reported in the through the thickness, thermal conductivity (80W/mK vs 8W/mK for the state-of-the-art SiC-SiC composite). Processing structure property relationship for the new class of SiC-SiC composites will be presented.
10:30 AM LL3.6
NEAR NET SHAPE SILICONIZED SILICON CARBIDE SHEETS BY CRUCIBLELESS INFILTRATION IN A PROTECTIVE ATMOSPHERE. L.M. Xiao, J.S. Yang, P. Kulkarni and X.F. Yang, Materials Research and Education Center, Auburn University, AL.
As the clock frequency and device density increase, the power consumption of IC continues to increase despite the operating voltage is declining. The latest microprocessor, Pentium II, consumes as much as 120 W in an area of 1 in2, and much more power is consumed in main frame computer and in multi-chip-module. Thermal consideration has become one important aspect in electronic packaging design. Materials with a high thermal conductivity and a CTE close to that of Si have been sought and various such materials have been developed. Examples include Si itself, AIN, SiC-Al composite, and graphite fiber- Cu composite, and even diamond and its composites have been explored. Such materials are, however, much more expensive than traditional packaging materials such as Al2O3 thermal plastics and conventional metals. It is thus highly desirable to develop new methods to fabricate materials with thermal conductivity considerably higher than that of Al2O3 at an equivalent or even lower cost. Materials with high thermal conductivity and low CTE are mostly refractory materials such as SiC, AiN, Mo, W, and diamond. Densification of such materials is difficult and thus considerably increases the cost of these materials. It is almost impossible to densify SiC powder without applying a very high pressure at a very high temperature, but a porous SiC preform can be easily infiltrated with Si, making it a fully dense component. Both Si and SiC have a high thermal conductivity, and the CTE of SiC is almost the same as Si. In addition, SiC-Si can be polished using conventional wafer processing to a nanometer surface finish, making it much superior to any other ceramic substrate. A SiC-Si composite thus is an ideal candidate for electronic packaging substrate if the cost can be brought down considerably. In the present study we have demonstrated that near-net-shape SiC-Si sheets can be produced rapidly by an infiltration technique. SiC-Si by our technique can be potentially cheaper than Al2O3 substrates. The mechanical properties, thermal characteristics, and other aspects of this composite are also evaluated.
10:45 AM LL3.7
HIGH THERMAL CONDUCTING ALLOYS AND INTERMETALLICS. Yoshihiro Terada and Tetsuo Mohri, Division of Materials Science and Engineering, Graduate School of Engineering, Hokkaido University, Sapporo, JAPAN.
Thermal conductivity is an important physical property for high temperature structural applications of metallic materials to avoid the degradation by local heat attack during operation. Rapid heat transfer afforded by high thermal conductivity enables efficient cooling, which suppresses the appearance of life limiting heat-attacked spots, thereby, resulting in lower thermal stresses and improved thermal fatigue. In metallic binary continuous solid solutions, a graphical representation of thermal conductivity as a function of composition is characterized by a U-shaped curve. A lattice ordering usually increases the conductivity, and the thermal conductivity of an intermetallic ordered compound is expressed as a sum of basic contribution of solid solution and enhanced effects due to the formation of a superlattice. In solid solutions, it is observed that the thermal conductivity decreases as the position of a solute increases in the horizontal direction from that of the solvent in the periodic table, which is a counterpart of Norbury-Linde rule proposed for electrical conductivity. Based on more systematic measurements for a series of solid solutions, we claim that a periodic table in a helical form most conveniently summarizes the alloying effects on the conductivity. In fact, the helical periodic table is utilized to seek for high conducting intermetallic compounds based on noble metals. It is confirmed that the candidate compounds Cu3Au, CuAu and AgMg show the maximum value of 157, 167 and 147 Wm 1K-1 at ambient temperature among L12, Ll0 and B2 compounds, respectively.