Alumina, thanks to its superior thermal and dielectric properties, has been the leading substrate over several decades, for power and microelectronics circuits. However, alumina lacks thermal stability since its temperature coefficient of resonant frequency (τf) is far from zero (−60 ppmK−1). The present paper explores the potentiality of a ceramic composite 0.83ZnAl2O4-0.17TiO2 (in moles, abbreviated as ZAT) substrates for electronic applications over other commercially-used alumina-based substrates and synthesized using a non-aqueous tape casting method. The present substrate has τf of + 3.9 ppmK−1 and is a valuable addition to the group of thermo-stable substrates. The ZAT substrate shows a high thermal conductivity of 31.3 Wm−1K−1 (thermal conductivity of alumina is about 24.5 Wm−1K−1), along with promising mechanical, electrical and microwave dielectric properties comparable to that of alumina-based commercial substrates. Furthermore, the newly-developed substrate material shows exceptionally good thermal stability of dielectric constant, which cannot be met with any of the alumina-based HTCC substrates.

/pdf/can-zinc-aluminate-titania-composite-be-an-alternative-for-26dkkmojmn.pdf

Can zinc aluminate-titania composite be an alternative for alumina as microelectronic substrate?

Ceramic matrix composites reinforced with carbon nanotubes are becoming increasingly popular in industry due to their astonishing mechanical properties and taking into account the fact that advanced production technologies make carbon nanotubes increasingly affordable In the present paper, the most convenient contemporary methods used for the compaction of molding masses composed of either technical ceramics or ceramic matrix composites reinforced with carbon nanotubes are surveyed This stage that precedes debinding and sintering plays the key role in getting pore-free equal-density ceramics at the scale of mass production The methods include: compaction in sealed and collector molds, cold isostatic and quasi-isostatic compaction; dynamic compaction methods, such as magnetic pulse, vibration, and ultrasonic compaction; extrusion, stamping, and injection; casting from aqueous and non-aqueous slips; tape and gel casting Capabilities of mold-free approaches to produce precisely shaped ceramic bodies are also critically analyzed, including green ceramic machining and additive manufacturing technologies

Methods Used for the Compaction and Molding of Ceramic Matrix Composites Reinforced with Carbon Nanotubes

The present work was initiated aiming at developing a high-performance film for LTCC application using a kind of polymeric dispersant in tape casting process of borosilicate-based glass/Al2O3 ceramics. The dispersion mechanism of the polymeric dispersant with the powders was analyzed in detail and the optimal amount of the dispersant addition was also determined through the sedimentation experiment. Its effects on the compactness, tensile strength and surface roughness of the films were analyzed. In addition, the sintering and microwave properties of the composite fired at 850 °C were also determined. For the application of tape technology, the co-firing compatibility between the composite and Ag electrodes at 850 °C was also verified. After testing and verification with different qualitative and quantitative instruments, a flexible film optimized by 1.5 wt% polymeric dispersant achieved the best overall performance.

Fabrication of a high-performance film based borosilicate glass/Al2O3 ceramics for LTCC application

Boron carbide is the third hardest material known, with a high melting point (2450 °C) and poor sintering ability. Therefore, boron carbide is a challenging material for shaping by conventional processing routes and can still be considered as unsuitable for commercial production of ceramics parts by additive manufacturing technologies. This work reports the first successful preparation of boron carbide ceramics fabricated by fused filament fabrication from a newly developed composite filament containing 65 wt% of micron-sized boron carbide powder dispersed in a thermoplastic binder. A commercial FFF desktop printer with a 0.40 mm nozzle was used for manufacturing of complex-shaped green bodies. Almost fully dense boron carbide ceramics with printed parts sized up to 4 centimeters and relative density higher than 96% after sintering were prepared. The DTA/TG analysis of composite filament and heat microscopy technique were used to set the debinding temperature program with critical temperature at 140 °C, due to the thermal decomposition of the binder. Microstructure SEM images after sintering showed excellent material homogeneity, while micro-CT images showed very well retained experimental shapes of collimator-like printed grids. The x-ray diffraction proved the presence of boron carbide phase with the free carbon phase at the level of about 1 wt% without significant influence on the measured hardness value of 29.88 ± 1.27 GPa. 

Preparation of Fully Dense Boron Carbide Ceramics by Fused Filament Fabrication (FFF)

B4C green tapes are prepared by aqueous tape casting and a spark plasma sintering (SPS) process using polyethylenimine (PEI) as dispersant, hydroxypropyl methyl cellulose (HPMC) as binder and polyethylene glycol (PEG) as plasticiser. The influences of solid content, dispersant content, mass ratio of plasticiser to binder (R value) and milling time on the slurry viscosity are studied. The samples are characterised by means of hardness tester, universal testing machine and scanning electron microscopy. The results indicate that the solid content of B4C slurry achieves 47.5 wt-% with milling time of 12 h when the content of PEI, HPMC and PEG is 1.5, 5 and 5 wt-%, respectively. The relative density of B4C ceramics subject to SPS at 1600°C and 50 MPa for 8 min is up to 97.2%. The Vickers hardness, flexural strength and fracture toughness of B4C ceramics reach 36.5 ± 0.7 GPa, 510.3 ± 19.4 MPa and 5.04 ± 0.29 MPa m−1/2, respectively.

Aqueous tape casting of B4C ceramics

Boron carbide green sheet processed by environmental friendly non-aqueous tape casting

The homogeneous B 4 C ceramics are successfully prepared through tape casting, laminating and hot pressing. The obtained B 4 C slurry exhibited a shear thinning behavior. After tape casting, both sides of the green sheets were smooth and homogeneous. After lamination and decomposition treatment developed in argon, hot press sintering of laminated boron carbide was proceed at 2000 °C. The results indicate that the strength and fracture toughness of B 4 C specimens are 585 MPa and 4.9 MPa m 1/2 , respectively. The primary fracture mode is an intergranular type. The reasons for the improvement in mechanical properties should lie in the tape casting processing technique and the presence of carbonaceous residues in specimen.

Preparation of homogeneous B4C ceramics with high toughness by tape casting

The water entry of two-dimensional body with flow separation is simulated based on potential theory and boundary element method. The double point model and four-order Runge-Kutta method and jet-cut model and free surface smooth technique and regrinding technique are used to assure the stability and accuracy of the numerical result. A flow separation model is introduced to simulate the water entry of two-dimensional body with knuckle. The free surface elevation and pressure distribution of wedge with knuckle are predicted and compared with other theory result. Good agreement between numerical result and other theory result is indicated that the numerical method is stability and effective.

Numerical Simulation of the Water Entry of Two-Dimensional Body with Flow Separation

Tape casting green sheet of boron carbide ceramic with adequate strength and flexibility was pre- pared by tape casting. The effects of the specific surface area, dispersant, binder, plasticizer and ball milling time on the viscosities of the slurries were discussed. An optimum ratio was acquired for tape casting of boron carbide powder, the results showed that the green tapes prepared with specific surface area of 3.82m 2 /g of boron carbide powder, 2.0wt.% of dispersant, 0.75~1 of the ratio of plasticizer and binder, 12~16h of ball milling time, could fabricated a better mechanical.

Preparation of Boron Carbide Slips by Tape Casting

The binder system removal was studied in a laminated B4C ceramics prepared by tape casting and lamination with castor oil, polyvinyl butyral(PVB) and di-n-butyl phthalate (DBP) as dispersant, binder and plasticizer, respectively. Thermo gravimetric analysis and Fourier transform infrared spectromer was used to examine the degradation of the binder system. The degradation behavior of the pure organics, single sheet and laminated B4C body were investigated. The results indicate that nitrog4en was selected as the binder system removal atmosphere and two decomposition temperature ranges was obtained for organics. A model based on diffusion can be used to predict the binder system removal time for a certain thickness of laminated B4C.

Binder System Removal from Laminated Boron Carbide Ceramics

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