Process optimization for glass to Kovar sealing

The effects of sealing atmosphere, sealing temperature, and sealing time on the surface appearance, leakage rate, bonding strength, bending frequency, and height of glass along the pins were investigated for glass to Kovar sealing. The results indicated that sealing atmosphere had an important impact on the surface appearance, and the extent of glass spattering was more serious as increasing the oxidizability of sealing atmosphere. With the extending of sealing time or the increasing of sealing temperature, the bonding strength between single oxide film (single FeO or single Fe₃O₄) and glass gradually increased, and the bending frequency almost maintained. The bonding strength between hilayer oxide film (FeO + Fe₃O₄ or Fe₃O₄ + Fe₂O₃) and glass was relatively higher and increased more quickly, however the bending frequency sharply decreased. The height of glass along the pins was not related to the type of the oxide; it reduced gradually with increasing sealing temperature, and also decreased rapidly with increasing sealing time until 140μm. The recommended sealing conditions included that the sealing atmosphere was weak reductive gas, the sealing temperature was about 980℃ and the sealing time was between 20 and 30 min.