Interfacial phenomena in electric
field-assisted anodic bonding
of Kovar/Al film-glass
field-assisted anodic bonding
of Kovar/Al film-glass
(Department of Materials and Environment Engineering,
East China Shipbuilding Institute,Zhenjiang 212003, P.R.China)
East China Shipbuilding Institute,Zhenjiang 212003, P.R.China)
Abstract: Anodic bonding of glass to Kovar alloy coated with Al film (Glass-Al film/Kovar) was performed in the temperature range of 513～713K under the static electric voltage of 500V in order to investigate the interfacial phenomena of Al-glass joint. The results reveal that Na and K ions within the glass are displaced by the applied field from the anode-side surface of the glass to form depletion layers of them. The K ion depletion layer is narrow and followed by a Kpile-up layer, and both the two layers are formed within the Na depletion layer. The width of the Na and K depletion layers is increased with increasing bonding temperature and time. The activation energies for the growth of both depletion layers were close to that for Na diffusion in the glass. TEM observations reveal that Al film coated at the surface of Kovar alloy is oxidized to amorphous Al2O3 containing a few of Fe, Ni and Co by oxygen ions from the glass drifted by high electric field during bonding. The amount of Fe ions diffusing into the glass adjacent to the anode is significantly low due to the presence of Al film between Kovar alloy and the glass. As a result, the amorphous reaction layer of Fe-Si-O in the glass near the interface is avoided which is formed in Kovar-glass joints.
Key words: anodic bonding; aluminum anode; glass; ions drift; depletion layer; interfacial reaction