Small, light weight and multifunctional electronic components are attracting much attention because of the rapid growth of the wireless communication systems and microwave products in the consumer electronic market. The component manufacturers are thus forced to search for new advanced integration, packaging and interconnection technologies. One solution is the low temperature cofired ceramic (LTCC) technology enabling fabrication of three-dimensional ceramic modules with low dielectric loss and embedded silver electrodes. During the past 15 years, a large number of new dielectric LTCCs for high frequency applications have been developed. About 1000 papers were published and ∼500 patents were filed in the area of LTCC and related technologies. However, the data of these several very useful materials are scattered. The main purpose of this review is to bring the data and science of these materials together, which will be of immense help to researchers and technologists all over the world. The comme...

Low loss dielectric materials for LTCC applications: a review

Liquid phase sintering (LPS) is a process for forming high performance, multiple-phase components from powders. It involves sintering under conditions where solid grains coexist with a wetting liquid. Many variants of LPS are applied to a wide range of engineering materials. Example applications for this technology are found in automobile engine connecting rods and high-speed metal cutting inserts. Scientific advances in understanding LPS began in the 1950s. The resulting quantitative process models are now embedded in computer simulations to enable predictions of the sintered component dimensions, microstructure, and properties. However, there are remaining areas in need of research attention. This LPS review, based on over 2,500 publications, outlines what happens when mixed powders are heated to the LPS temperature, with a focus on the densification and microstructure evolution events.

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Review: liquid phase sintering

Grain growth in a high-purity ZnO and for the same ZnO with Bi2O3 additions from 0.5 to 4 wt% was studied for sintering from 900° to 1400°C in air. The results are discussed and compared with previous studies in terms of the phenomenological kinetic grain growth expression: Gn—Gn0=K0t exp(—Q/RT). For the pure ZnO, the grain growth exponent or n value was observed to be 3 while the apparent activation energy was 224 ± 16 kJ/mol. These parameters substantiate the Gupta and Coble conclusion of a Zn2+ lattice diffusion mechanism. Additions of Bi2O3 to promote liquidphase sintering increased the ZnO grain size and the grain growth exponent to about 5, but reduced the apparent activation energy to about 150 kJ/mol, independent of Bi2O3 content. The preexponential term K0 was also independent of Bi2O3 content. It is concluded that the grain growth of ZnO in liquid-phase-sintered ZnO-Bi2O3 ceramics is controlled by the phase boundary reaction of the solid ZnO grains and the Bi2O3-rich liquid phase.

Grain Growth in Sintered ZnO and ZnO-Bi2O3 Ceramics

This chapter contains sections titled: Introduction, Theoretical Work, Experimental Work, Summary, References

Sintering in the Presence of a Liquid Phase

Grain growth of ZnO during the liquid-phase sintering of binary ZnO–Bi2O3 ceramics has been studied for Bi2O3 contents from 3 to 12 wt% and sintering from 900° to 1400°C. The results are considered in combination with previously published studies of ZnO grain growth in the ZnO–Bi2O3 system. For the Bi2O3 contents of the present study, the rate of ZnO grain growth is found to decrease with increasing Bi2O3. Activation analysis, when combined with the results of similar analyses of the previous studies, reveals a change in the rate-controlling mechanism for ZnO grain growth. Following a low-Bi2O3-content region of nearly constant activation energy values of about 150 kJ/mol, further Bi2O3 additions cause an increase of the activation energy to about 270 kJ/mol. consistent with accepted models of liquid-phase sintering, it is concluded that the rate-controlling mechanism of ZnO grain growth during liquid-phase sintering in the presence of Bi2O3 changes from one of a phase-boundary reaction at low Bi2O3 levels to one of diffusion through the liquid phase at about the 5 to 6 wt% Bi2O3 level and above.

Grain Growth of ZnO during Bi2O3 Liquid-Phase Sintering

Observations of microstructure changes in several systems and the rate of densification during sintering of magnesium oxide, titanium carbide, and tungsten carbide in the presence of a liquid phase indicate that the densification rate is controlled by diffusion through a liquid film between particles. Dependence of the sintering rate on time, particle size, and temperature are in agreement with predictions. Theoretical estimations of the sintering rate are in reasonable agreement with experimental measurements.

E. Niki

Papers

Sintering of Oxide and Carbide-Metal Compositions in Presence of a Liquid Phase