Papers by Keyword: CTE

Abstract: The effective properties of metal matrix composites (MMCs) depend on matrix material and reinforcement property specifications as well as bonding at interphase. The use of numerical methods such as finite element (FE) and mean field homogenization (MFH) can assist in predicting MMC properties thus reducing time and cost of optimizing composite properties through experiments. In the present work, a multiscale representative volume element (RVE) of the microstructure of reduced graphene oxide (rGO) reinforced Aluminium (Al) matrix composite (rGO/Al) is created in MSC DigiMat and analysed using Abaqus software. The effect of porosity and rGO reinforcement on thermal conductivity and strength of the rGO/Al composites is studied. The variation in thermal conductivity between FE-RVE and experimental data is a maximum of 2.2% and a minimum of 0.07% for rGO reinforcement of 1 wt.% and 3 wt.% respectively. The results show good agreement between FE-RVE simulation, MFH and experimental data. This approach can provide an efficient technique for selecting matrix and reinforcement phase properties for MMC fabrication. Keywords: Al/rGO composite, Multiscale finite element-representative volume, Thermal and mechanical properties

Abstract: Solid state sintered pellets of barium hexaferrite were performed. The Curie temperature of BaFe₁₂O₁₉ pellets were measured with differential scanning colorimetry (DSC). The coefficient of thermal expansion (CTE) of pellets was defined above and below the Curie temperature. The Curie temperature calculated basedon the dilatometry is are in good agreement with the DSC measurements.

Abstract: Spherical silica particles with mean diameter 350 nm, 500 nm and 1000 nm were used to modify o-cresol-novolac epoxy resin (ECN) at a ranging constant weight fraction from 0 to 20 wt%. The effects of particle size and fillers content on the impact strength, flexural modulus, dynamic mechanical analysis (DMA), coefficient of thermal expansion (CTE), dielectric properties and bulk resistivities of epoxy composites filled with spherical silica particles were investigated. The results revealed that the impact strength and flexural modulus showed significant improvements with the addition of spherical silica particles. The glass transition temperature (T_g) of composites was higher than that of pure epoxy. The maximum increment of T_g was 34 °C by the addition of 2 wt% D500. The CTE of the composites with different size silica exhibit much lower dimension changes than that of pure epoxy. The dielectric constant was decreased with the addition of spherical silica particles. However, the particle size exhibited weakly effect on the dielectric properties. The bulk resistivities of the composites have greatly improved compared to the pure epoxy and increase with decreasing the particle size.

Abstract: In this paper, the influences of sintering conditions on the phase transformation, microstructure, bulk density, bending strength, coefficient of thermal expansion, and dielectric properties of Li₂O-Al₂O₃-SiO₂ glass-ceramic were investigated. Conventional melt-quenching method was used to synthesize this glass-ceramic. Scanning electron microscopy, X-ray diffractometer and differential thermal analysis were employed to study this material. The XRD data show that Li₂OAl₂O₃7.5SiO₂ is the main crystalline phase of this glass-ceramic. ZrO₂ and CaMgSi₂O₆ are the two other phases in this glass-ceramic. The increasing sintering temperature and soaking time affect the phase composition obviously, which lead to the obvious variations of microstructure, mechanical, dielectric and thermal properties of this glass-ceramic. Sintering temperature and time play a key role in the sintering of Li₂O-Al₂O₃-SiO₂ glass-ceramic. The sample sintered at 800 °C for 30 min showed good microstructure, low sintering temperature of 800 °C, high density of ~2.6 g/cm³, excellent dielectric properties (εr: ~6.9, tan δ: ~2*10^-3), good bending strength of 143 MPa and adjustable CTE from 1.1 to 2.7 *10^-6 K^-1 close that of silicon. These results mean that the obtained LAS glass-ceramic can be used in the application of LTCC substrate, especially, the manufacture of the substrate of silicon.

Abstract: Material with ultra-low coefficient of thermal expansion (CTE) is required for mounting camera and other optical elements in satellite systems. Invar (64 Fe 36Ni) has been the work-horse material for this purpose. In recent years, modified version of conventional invar i.e. Superinvar with 5% cobalt (replacing 5% nickel) is being used to further bring down the errors in camera mountings due to thermal expansion. Processing of this alloy poses many challenges due to its requirement of ultra-low CTE. In the present work, melting and thermomechanical processing parameters were selected to meet the specified requirement of the alloy. The alloy was melted through vacuum induction melting process to obtain uniform and homogeneous chemistry and properties. Virgin raw material was used to achieve lowest carbon and manganese contents. Chemical composition thus obtained is found to be within the specification. Material was hot worked to refine the microstructure. Three different sizes of forged blocks were produced. Hot worked material was heat treated to obtain desirable and stable microstructure. Heat treatment cycle for stabilization was selected and used to retain carbon in the solution and minimize temporal growth. Mechanical properties (tensile strength and modulus of elasticity) and physical properties (CTE, thermal conductivity) were evaluated. Properties were found to be meeting the specification. It is observed that the material shows uniform single phase austenitic microstructure. The paper presents details of the process selection and challenges in processing of this alloy to obtain the targeted CTE < 0.6x10^-6 per °C in the temperature range of 25°C to 150°C along with other desired mechanical properties.

Abstract: GaN High Electron Mobility Transistors (HEMTs) on SiC have gained remarkable attention as these devices are revolutionizing the power and radio frequency (RF) electronics markets. Although significant advances have been made in transistor technology innovations, innovations pertaining to the backside process technology have been noticeably few. This paper will address and focus on innovations in the backside processing of GaN on SiC devices. A series of innovations in backside processing enable through SiC and GaN via etch rates to exceed 1.5 micron/minute. Wafer dicing process innovations afforded a >4x improvement in sawing throughput and a >6x improvement in blade lifetime through the novel addition of ultrasonic power to a conventional sawing tool.

Abstract: Energy efficiency is becoming more and more important in high temperature processes or for high temperature applications. In order to achieve thermally efficient processes, heat accumulators and heat exchangers are increasingly being used to store or to recover the process heat [1]. Currently used commercial heat exchanger systems are based on stacked plates or tubes. Primarily they are produced from metals which have a high thermal conductivity and show gas-tightness. Ceramics or ceramic matrix composites (CMC) are novel material candidates due to their higher resistance in severe environments, their ability to withstand extremely high operating temperatures and especially, their high thermal shock resistance. In order to fabricate HX with ceramic designs, joining is the key technology to perform complex shaped components [2].

Abstract: Glass-ceramic materials of the Li₂O-ZnO-SiO₂ system, with various amounts of TiO₂ added, have been prepared. The appropriate heat treatment temperatures were selected according to the information provided by the differential thermal analysis (DTA). X-ray diffraction (XRD) analysis demonstrated that in the LZS glass-ceramics system, the main phases are Li₂ZnSiO₄, cristobalite, tridymite and quartz. The scanning electron microscopy (SEM) revealed that crystals appear as lamellar and spherical particles in the glass-ceramics samples. In addition, the average coefficient of the thermal expansion (CTE) values first decreased, then increased and finally tended to flatten. When the content of TiO₂ increased to 6%, the CTE value decreased to 9.15×10^-6/K, reached the lowest value. When the content of TiO₂ increased to 10%, the CTE value reached highest value 13.90×10^-6/K.

Abstract: Managing the emerging internal mechanical stress in chips particularly if they are 3D-tscked is a key task to maintain performance and reliability of microelectronic products. Hence, a strong need of a physics-based simulation methodology/flow emerges. This physics-based simulation, however, requires materials parameters with high accuracy. A full-chip analysis can then be performed, balancing the need for local resolution and computing time. Therefore, effective composite-type materials data for several regions of interest are needed. Advanced techniques to measure FEA-and design-relevant properties such as local and effective Youngs modulus and effective CTE values were developed and described in this paper. These data show a clear orientation dependence, caused by the chip design.

Abstract: The element W, Mo with paremagnetism and grain refinement is selected according to the theory of magnetostrictive and fine grain strengthening method. The sample with low coefficient of thermal expansion (CTE) and high strength are made by W and Mo alloying of Fe-Ni36, forging and heat treatment. The mechanism of low coefficient of thermal expansion and high strength is analyzed by means of the results of Chemical analysis, metallographic and scanning electron microscopy, grain size, micro-hardness and CTE testing. The result shows: the strength of matrix is improved by W and Mo alloying, the CTE is lower at the same time.