Densification of Compacted Magnesium Alumino-Silicate Glass Powders

Abstract

The ceramics obtained by sintering glass powders with various chemical compositions have been used for substrates in multilayer packaging, In previous study in MgO-Al2O3-SiO2 system, it was found that the sinterability of glass powders much differed depending on the compositions. To ascertain the origin of this difference in sintering behavior, the viscosity of glasses at sintering temperatures and isothermal shrinkage curves were measured. Temperatures at which crystals precipitated in glasses and activation energies for crystallization were determined with differential thermal analysis. Compacted glass powders sintered by a viscous flow mechanism at temperature range from 830° to 860°C at which the viscosity of glasses decreased as low as about 109 poise. No densely sintered body was obtained by heating a compacted glass powder with the cordierite composition, because cordierite crystals have precipitated during the initial stage of sintering due to its low activation energy. A compacted glass powder containing a fairly large amount of MgO, and low amounts of Al2O3 and SiO2 comparing with the cordierite composition sintered densely, due to the cordierite crystals precipitated in the glasses after the densification have been completed in consequence of increasing stability of the glass. A compacted glass powder with a high SiO2 content did not sinter, In this compact, cristobalite crystals precipitated at grain boundaries (necks of glass grains) in the initial stage of sintering and prevented the densification of the compacts by a viscous flow mechanism.