Ag diffusion inhibition and enhanced flexural strength in low temperature co-fired CaO-Al2O3-B2O3-SiO2 glasses

Abstract

This work explores Ag diffusion mechanism and mechanical strength in low-k 35 wt% CaO-33 wt% Al2O3-15 wt% B2O3-17 wt% SiO2 glasses with different amounts of Al2O3 (0–30 wt%) and SiO2 (0–8 wt%) ceramic-filler additions using low temperature co-firing with Ag electrode. The 8 wt% Al2O3-added specimen displays the highest flexural strength of ∼268 Mpa due to higher densification and less pores, which could be attributed to well wetting at boundaries between glasses and Al2O3 ceramics. The crystalline SiO2-ceramic-added glasses can effectively inhibit diffusion of Ag ions with a higher diffusion activation energy of 391 kJ/mol in the 8 wt% SiO2-ceramic-added specimen. A model of Ag diffusion inhibition is proposed based on percolation clusters of broken bonds for SiO2-added CaO-Al2O3-B2O3-SiO2 glasses. We propose that percolation clusters of broken bonds were increased in the SiO2-ceramic-added glass matrix at T > Tg and clusters of oxygen ions can trap Ag ions to form Ag-O bonds to reduce thermal diffusion of Ag ions. The Al2O3 and SiO2 co-added CaO-Al2O3-B2O3-SiO2 glasses can be considered as a candidate for low temperature co-fired microwave dielectric ceramic substrate.