Low-dielectric compositions with controlled crystallization and thermal expansion

摘要

Cristobalite is formed in an initially amorphous low-dielectric lead borosilicate glass at 700-900℃. With added alumina content greater than a critical value, however, the cristobalite formation in the lead borosilicate glass is completely inhibited. The critical alumina content is found to decrease with decreasing alumina particle size but with increasing sintering temperature. This result is attributed to a strong coupling reaction between Al~(3+) from alumina and Na~+ and Pb~(2+) from lead borosilicate glass. The resulting cristobalite-free glass composite has a dielectric constant of 5.0 at 1 MHz and a thermal expansion coefficient of (2.5 - 4.0) x 10~(-6) K~(-1) in the temperature range of 25-200℃.