Sinterability, microstructure and properties of glass/ceramic composites

Two series of glass/ceramic composites, glass/mullite (MG) and glass/spinel (SG) were prepared from borosilicate glasses and mullite or magnesium aluminate spinel. Both composites contain 50, 60, 70, 80 wt.% borosilicate glass. The formation of cristobalite in the glass matrix of low firing glass/ceramic composite substrates limits the efficiency of the ceramic substrate when it is used in circuit boards. In the present study, addition of mullite or spinel to a borosilicate glass as a ceramic filler caused the diffusion of mullite or spinel constituents into the glass matrix and prevented the formation of a cristobalite. Spinel suppresses cristobalite formation more effectively than mullite, and results in lower dielectric constant and thermal expansion coefficients.