Dielectric ceramic composition

Cera.micA.bla.tors, Several types of subliming or melting ceramic ablators have been used or considered for use in dielectric appHcations particularly with quartz or boron nitride [10043-11 -5] fiber reinforcements to form a nonconductive char. Fused siHca is available in both nonporous (optically transparent) and porous (sHp cast) forms. Ford Aerospace manufactures a 3D siHca-fiber-reinforced composite densified with coUoidal siHca (37). The material, designated AS-3DX, demonstrates improved mechanical toughness compared to monolithic ceramics. Other dielectric ceramic composites have been used with performance improvements over monolithic ceramics (see COMPOSITE MATERIALS, CERAMIC MATRIX). 

Rao, Y., Ogitani, S., Kohl, P, and Wong, C.P., High dielectric constant polymer-ceramic composite for embedded capacitor application, in Proceedings of the International Symposium on Advanced Packing Materials Processes, Properties, and Interfaces, IEEE, Piscataway, NJ, 2000. 

Q. Zeng, W. Li, J. L. Shi, J. K. Guo, Fabrication and Microwave Dielectric Properties of a New LTCC Ceramic Composite Based on Li20-Nb20s-Ti02 System, Mater. Lett., 11, 3203-6 (2006). 

Ceramic matrix composites are under active consideration for low-observable military applications, where dielectric properties are a key performance factor. The frequency range of interest is the 8-12 GHz microwave range. The composite system must have low electrical conductivity. The SiOC-Nextel 312 system meets that requirement (as compared to ceramic composites made with conductive silicon carbide fibers). 

R. D. Yasukawa, D. G. Polensky, R. Y. Leung, S. T. Gonczy, J. G. Sikonia, Blackglas Ceramic Matrix Composites with Dielectric Properties and Fibrous Fracture, Presentation at 2d Aimual Ceramic Composites and Structures Meeting, USAF, West Palm Beach, FL, Oct. 20-22, 1992. 

Figure 9.2. A ceramic composite with a high dielectric constant that is less easily saturated than its operative component." Published with permission from the Journal of Materials Education.

To prevent the BaTi03-based dielectric ceramics from reduction, essential points of the composition designing are [1-3] ... 

A description of the application of ceramic and photopolymer technologies to achieve high-resolution electronic patterns follows. The first section discusses ceramic dielectric vias, and the second, conductive circuitry. Improved photosensitive ceramic coating compositions and more particularly, compositions that function as precursors to fired dielectric ceramics, are mainly useful in preparation of multilayer thick-film substrates. 

Another glass-ceramic composite with a higher dielectric constant than that of MLS-1000 has been achieved with a product called MLS-40. The composite contains a glass-ceramic derived from the Si02-Ti02—Nd205 system as well as a sintered ceramic. The properties of the product (composite) are also shown in Table 4-21. 

The use of polytetrafluoroethylene or PTFE for printed wiring substrate fabrication is a relatively well-established practice brought about by the need for improved high-frequency materials. The critical properties in this field of application are a low dissipation factor, a uniform dielectric constant which exhibits little variation with frequency over a wide bandwidth up to 15 GHz, combined with environmental and temperature stabilities. These properties can be achieved in a number of teflon/glass or teflon/glass/ceramic composites based on both fabrics and random glass. The dissipation factor at 1 MHz is more than 100 times less than a typical epoxy FR4, as shown in Table 9.4. 

As we explained in Chapter 1, the main types of LTCC dielectric ceramics are glass/ceramic composites and crystallized glass. The characteristics required of the raw materials differ for each type. 

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