Low Temperature Sealing Process and Properties of Kovar Alloy to DM305 Electronic Glass

The low temperature sealing of Kovar alloy to DM305 electronic glass was realized by using lead-free glass solder of the Bi2O3-ZnO-B2O3 system in atmospheric environment. The sealing process was optimized by pre-oxidation of Kovar alloy and low temperature founding of flake glass solder. The effects of sealing temperature and holding time on the properties of sealing joint were studied by means of X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS), etc. The results showed that the pre-oxidized Kovar alloy and DM305 electronic glass were successfully sealed with flake glass solder at the sealing temperature of 500 °C for 20 min. Meanwhile, the joint interface had no pores, cracks, and other defects, the shear strength was 12.24 MPa, and the leakage rate of air tightness was 8 × 10−9 Pa·m3/s. During the sealing process, element Bi in glass solder diffused into the oxide layer of Kovar alloy and DM305 electronic glass about 1 μm, respectively.

Effects of Laser Radiation on the Wetting and Diffusion Characteristics of Kovar Alloy on Borosilicate Glass

The purpose of this study was to investigate the advantages of laser surface melting for improving wetting over the traditional approach. For comparison, kovar alloy was preoxidized in atmosphere at 700 °C for 10 min, and then wetted with borosilicate glass powder at 1100 °C with different holding time in atmosphere. The proposed approach used a Nd:YAG laser to melt the surface of the kovar alloy sample in atmosphere, then wetted with borosilicate glass powder at 1100 °C with the same holding time. The laser melted surface shows a decrease in contact angle (CA) from 47.5 deg to 38 deg after 100 min. X-ray photoelectron spectroscopy (XPS) analysis shows that the surface and adjacent depth have higher concentration of FeO for laser treated kovar (Kovar(L)) than that on traditional thermal treated kovar (kovar(P)). This is attributed to the following improved wetting and diffusion process. The adhesive oxide layer formed on kovar (L) may enhance the oxygen diffusion into the substrate and iron diffusion outward to form an outside layer. This is an another way to enhance the wetting and diffusion process when compared to the delaminated oxide scales formed on kovar (P) surface. The diffusion mechanisms were discussed for both approaches. Scanning electron microscope (SEM) revealed that an iron oxide interlayer in the joint existed under both conditions. Fayalite nucleated on the iron oxide layer alloy and grew into the glass. In both cases, neither Co nor Ni were involved in the chemical bonding during wetting process. The work has shown that laser surface melting can be used to alter the wetting and diffusion characteristics of kovar alloy onto borosilicate glass.