Glass and ceramic sealing

With the rapid development of modern science and technology, the requirements for new engineering materials are higher and higher in the high-tech fields such as electronic industry, nuclear energy industry, aerospace and modern communication. As we all know, the engineering ceramic materials (also known as structural ceramics) developed by modern technology are new engineering materials to adapt to the development and application of modern high technology. At present, it has become the third engineering material after metal and plastic. This material not only has high melting point, high temperature resistance, corrosion resistance, wear resistance and other special properties, but also has radiation resistance, high frequency and high voltage insulation and other electrical properties, as well as sound, light, heat, electricity, magnetic and biological, medical, environmental protection and other special properties. This makes these functional ceramics widely used in the fields of electronics, microelectronics, optoelectronic information and modern communication, automatic control and so on. Obviously, in all kinds of electronic products, the sealing technology of ceramics and other materials will occupy an extremely important position.

The sealing of glass and ceramic is a process of connecting glass and ceramic into a whole structure by proper technology. In other words, the glass and ceramic parts using good technology, so that two different materials combined into a dissimilar material joint, and make its performance meet the requirements of the device structure.

The sealing between ceramic and glass has been developed rapidly in recent years. One of the most important functions of sealing technology is to provide a low-cost method for manufacturing multi-component parts. Because the forming of ceramics is limited by parts and materials, it is very important to develop effective sealing technology. Most ceramics, even at high temperature, also show the characteristics of brittle materials, so it is very difficult to manufacture complex shape parts through the deformation of dense ceramics. In some development plans, such as the advanced thermal engine plan, some single parts can be manufactured through mechanical processing, but it is difficult to achieve mass production due to the constraints of high cost and processing difficulty. However, the porcelain sealing technology can connect the less complicated parts into various shapes, which not only greatly reduces the processing cost, but also reduces the processing allowance. Another important role of the sealing technology is to improve the reliability of the ceramic structure. Ceramics are brittle materials, which are very dependent on defects, Before the complex shape is formed, it is easy to inspect and detect the defects of the simple shape parts, which can greatly improve the reliability of the parts.

Sealing method of glass and ceramic

At present, there are three kinds of ceramic sealing methods: metal welding, solid phase diffusion welding and oxide glass welding（ 1) Active metal welding is a method of welding and sealing directly between ceramic and glass with reactive metal and solder. The so-called active metal refers to Ti, Zr, HF and so on. Their atomic electronic layer is not fully filled. Therefore, compared with other metals, it has greater liveliness. These metals have great affinity for oxides, silicates and other substances, and are most easily oxidized under general conditions, so they are called active metals. At the same time, these metals and Cu, Ni, AgCu, Ag, etc. form intermetallic at temperatures lower than their respective melting points, and these intermetallic can be well bonded to the surface of glass and ceramics at high temperature. Therefore, the sealing of glass and ceramic can be successfully completed by using these reactive gold and corresponding explosive.

(2) Peripheral phase diffusion sealing is a method to realize the whole sealing under certain pressure and temperature when two pieces of cluster materials contact closely and produce certain plastic deformation, so that their atoms expand and contract with each other.

(3) Glass solder is used to seal the glass and meat porcelain.

Sealing of solder glass

(1) Glass, ceramic and solder glass should be selected as sealing materials first, and the foot expansion coefficient of the three should match, which is the primary key to the success of sealing. The other key is that the selected glass should be well wetted with glass and ceramic during sealing, and the sealed parts (glass and ceramic) should not have thermal deformation, Finally, all parts after sealing should have certain strength.

(2) The processing quality of parts: the sealing end faces of glass parts, ceramic parts and solder glass must have higher flatness, otherwise the thickness of solder glass layer is not consistent, which will cause the increase of sealing stress, and even lead to the explosion of porcelain parts.

(3) The binder of solder glass powder can be pure water or other organic solvents. When organic solvents are used as the binder, once the sealing process is not properly selected, the carbon will be reduced and the solder glass will be blackened. Moreover, when sealing, the organic solvent will be decomposed, and the harmful gas to human health will be released. Therefore, choose pure water as much as possible.

(4) The thickness of pressure solder glass layer is usually 30 ~ 50um. If the pressure is too small, if the glass layer is too thick, the sealing strength will be reduced, and even Lake gas will be produced. Because the sealing end face can not be the ideal plane, the pressure is too large, the relative thickness of the coal glass layer varies greatly, which will also cause the increase of sealing stress, and even cause cracking.

(5) The specification of stepwise heating up is adopted for the crystallization sealing, which has two purposes: one is to prevent the bubble in the solder glass layer caused by the rapid development of moisture at the initial stage of heating up, and the other is to avoid the cracking of the whole piece and the glass due to the uneven temperature due to the rapid heating up when the size of the whole piece and the glass piece is large. As the temperature increases to the initial temperature of the solder, the solder glass begins to break out. High sealing temperature, long sealing time, and the amount of product break out are beneficial to the improvement of the sealing strength, but the air tightness decreases. The sealing temperature is low, the sealing time is short, the glass composition is large, the gas tightness is good, but the sealing strength decreases, In addition, the number of analytes also affects the linear expansion coefficient of the solder glass. Therefore, in order to ensure the sealing quality, in addition to selecting the appropriate solder glass, the reasonable sealing specification and sealing process should be determined according to the test face. In the process of glass and ceramic sealing, the sealing specification should also be adjusted according to the characteristics of different solder glass.