Interfacial Phenomena in Anodic Bonding of Glass to Kovar Alloy
Morsy Amin MORSY, Keito ISHIZAKI, Kenji IKEUCHI, Masao USHIO
Interfacial microstructures have been investigated for the anodically-bonded joint of borosilicate glass to Kovar alloy in order to get better insight into its mechanism. SEM observations of the joint interface revealed that the applied field displaced Na and K ions from the anode-side of glass to form depletion layers of these elements. Potassium also showed a pile-up layer following the K depletion layer within the Na depletion layer. Potassium depletion layer appeared as a zone darker than the bulk glass with a clear contrast. The thickness of alkali-depletion layers increased with the increase in bonding time, and then approached a saturation value. From the estimated activation energies of growth of Na and K depletion layers, it is suggested that the growth of Na and K layers is controlled by the diffusion of No. TEM observations revealed the formation of an amorphous reaction layer of about 0.1μm thickness, which consisted of a complex oxide of iron and silicon. An iron-rich crystalline layer of about 10 nm thickness was also observed between the amorphous reaction layer and the Kovar alloy substrate. The results of the present study are discussed on the basis of elements migration under the influence of electric fields generated in the glass.