Crystallization and wetting of ZnO-Al2O3-B2O3-SiO2 glass-ceramic for sealing to Kovar alloy

A new type of ZnO-Al₂O₃-B₂O₃-SiO₂ glassceramics seals to Kovar in electronic packaging was developed, whose coefficient of thermal expansion (CTE) and electrical resistance were 5.2 × 10⁻⁶/°C and over 1 × 10¹³ Ω·cm, respectively. The major crystalline phases in the glass-ceramics seals were ZnAl₂O₄, ZnB₂O₄ and NaSiAl₂O₄. The dielectric resistance of the glass-ceramic could be remarkably enhanced through the control of the alkali metal ions into the crystal lattices. It was found that the crystallization happened first on the surface of the sample, leaving the amorphous phase in the inner parts, which makes the glass suitable for sealing. The glass-ceramic showed better wetting on the Kovar surface, and sealing atmosphere and temperature showed great effect on the wetting angle. Strong interfacial bonding was obtained, which was mainly attributed to the interfacial reaction between SiO₂ and FeO or Fe₃O₄. This paper was presented at 2008 MRS International Materials Research Conference and won the student best paper award of the conference.