We have measured in‐plane stresses developed in a borosilicate glass (BSG) film during its constrained sintering on a rigid substrate. Samples were prepared by casting BSG slurries on a silicon substrate and sintered inside a hot stage at 715°C just above the glass‐softening temperature. Inplane stresses from the constrained‐film sintering were determined by wafer‐curvature measurements using an optical system. The measured stresses were tensile and rose rapidly from zero to a maximum level of 20 kPa during the initial stage of sintering and gradually decreased to zero at the final stage; these stresses were considerably smaller than those calculated from available microstructural models. We also measured the densification profiles of the free and constrained films. The stresses had no apparent effect on the densification profile of the constrained film up to 90% relative density; but beyond that, the densification kinetics were reduced in the constrained film. We believe that the stresses could have prevented a few large pores from shrinking during the initial stage of sintering, which then leads to an overall lower density and larger pores in the constrained film.

The kinetics of constrained-film sintering were studied in a borosilicate glass (BSG) + silica system because of their applications in microelectronic packaging technologies. Samples with a silica content by 20% by volume were prepared from slurries of powder mixtures in a commercial polyvinyl butyral (PVB) binder solution. Constrained films about 0.2 mm thick were formed by doctor-blade casting the slurries on silicon wafers. Free-standing films about 0.6 mm thick were also produced by casting the slurries on a treated mylar sheet for easy lift-off. Sintering experiments were carried out in a hot stage at temperatures between 715 °C and 775 °C. Shrinkage profiles of the free and constrained (shrinkage in thickness only) films were determined in situ using a custom-designed optical system. The densification rates measured in the constrained films were slower than those in the free films. However, the substrate constraint had no effect on the activation energy of densification which was found equal to 385 ± 10 kJ/mol, the same for both free and constrained films. A relation between the constrained-film and free-film densification profiles was derived using the viscous analogy for the constitutive equations of a porous sintering body.

Mg 4 Nb 2 O 9 ceramics have been prepared by a hydrothermal synthesis in order to reduce the sintering temperature. The sintering and microwave dielectric properties of the hydrothermally processed Mg 4 Nb 2 O 9 were studied under various sintering temperatures ranging from 900 to 1300°C. The highest Q×f o value of 26,069 GHz was obtained at the sintering temperature of 1300°C and is attributed to the increased density and appropriate grain growth. t f value of −17.1 ppm/°C was improved by the addition of TiO 2 and t f value of 6.7 ppm/°C was obtained at 20 wt% TiO 2 . Chemical compatibility of Mg 4 Nb 2 O 9 with Ag was tested to identity the possibility of using Mg 4 Nb 2 O 9 for an LTCC application. Since any secondary phase was not observed in the XRD pattern of the mixtures of Mg 4 Nb 2 O 9 and Ag powder heat treated at 900°C, it was considered that the Mg 4 Nb 2 O 9 system is applicable to the multilayer microwave devices using Ag as an electrode.

The shear viscosity of borosilicate glass (BSG) + silica powder compacts was determined during isothermal sintering at temperatures between 665 and 715°C. An optical system was used to measure in situ the densification profiles of the compacts in the form of thick films constrained on a rigid substrate and in-plane stresses generated during sintering. The shear viscosity as a function of relative density was calculated from these measurements by using Scherer's viscous constitutive equations for a porous sintering body. The shear viscosity for samples with silica contents from 0 to 20 vol% generally showed a slow increase with density in the low-density regime followed by a rapid rise after some threshold density that decreased with either increasing silica powder content or decreasing sintering temperature. The dependence of shear viscosity on relative density is consistent with results from sinter-forging experiments. However, results obtained from pure BSG compacts also revealed strong dependence of shear viscosity on temperature and microstructure, which has been all but neglected in previous theoretical studies.