Glass Sintering Process for Hermetic Connectors
Compared with plastic sealed connectors, glass and metal sealed connectors have the following characteristics:
1) Better mechanical strength
When glass and metal are sealed, the glass liquid and the metal oxide layer infiltrate each other to form a mixed chemical bond. The bonding force of this chemical bond is much greater than the bonding force of plastic to metal. Therefore, the connector encapsulated with glass and metal has sufficient tensile and torsional strength.
2) High temperature resistance
Glass is an inorganic non-metallic material, it has a high softening point temperature, and it will not release any harmful components when used in a high temperature environment. Plastics are not only not resistant to high temperatures, but also easily volatilize harmful components in high temperature environments. This is why some connectors, especially connectors that need to be completely sealed at one end and used as a working interface (such as program controllers and millimeter-wave coaxial connectors, etc.), cannot use plastic as an insulating material.
3) Good sealing
The leakage rate can reach 10Pa·cm/s. In addition, glass, like general insulating materials, has good electrical performance parameters, and the insulation resistance and dielectric withstand voltage of glass can fully meet the design requirements of the connector. It also has strong corrosion resistance and is suitable for harsh environments.
Generally speaking, the production process of plastic sealed connectors is relatively simple and the production cost is low, but its reliability is not as good as that of glass-sealed connectors. The connector with glass as insulating material, although the production process is more complicated and the cost is higher, but it has some characteristics that cannot be replaced by plastic sealed connectors. In the field of aviation and aerospace technology, there are many connectors with special requirements. Plastic sealing cannot meet their performance requirements. Only glass and metal sealing can meet the high-precision and high-reliability requirements of the connector.
Introduction to Glass
Glass is a solid insulating material with an amorphous structure. Therefore, there is no obvious melting point and freezing point. The main component of glass is anhydrous silicic acid (SiO). If its purity is high, the melting point of glass is extremely high and processing is difficult. Therefore, during processing and manufacturing, alkali metals, alkaline earth metals, or other metal oxides are added to lower the melting point and reduce the difficulty of processing. However, the added metal alkali ions are helpful to conduction, which will reduce the insulation resistance and affect the insulation performance of the glass.
The following introduces several commonly used glass:
Alkali glass: also known as ordinary glass. Adding 15% NasO and 5-7% CaO is called sodium glass; adding 15% K; 0 and 5-7% CaO is called sodium glass. The biggest advantage of these two kinds of glasses is that the softening temperature is very low, only about 550~600°C, so the processing is easy and the price is cheap. But the insulation is poor, so it can only be used in general insulation occasions, such as doors and windows, glass bottles, and light bulbs.
Lead glass: Add more than 20% PbO to reduce alkaline components. The softening temperature is about 400~600℃, and it is easy to process. Excellent insulation, mainly used in light bulbs, vacuum tubes. Due to the high content of PbO, high dielectric constant, and small dielectric loss Tan 6, it can be used as a dielectric material for capacitors. In addition, lead glass has a large light refraction index and can be used for optical and decorative purposes.
Borosilicate glass: Add 10% B;0 to reduce the alkaline component, and lower the softening temperature (500~700°C) without reducing its insulation, so as to facilitate its processability. Due to the small linear expansion coefficient, it can withstand rapid cooling and rapid heating, has stable chemical properties, and has good high-frequency characteristics. It can be used as high-frequency barriers and brackets, large vacuum tube tube balls, and boiler water level gauges.
Quartz glass: The powder of quartz or silica is heated to a high temperature of 1800°C and melted to make a high-purity amorphous material. Because it does not contain alkaline additives, it has excellent insulation and low dielectric loss, and is suitable for high-frequency insulating materials.
Glass fiber: long fibers are made by melting borosilicate glass with an alkali content of less than 0.8% in a pot. There are many small holes at the bottom of the pot. The rolls are wound into fibers, gathered into bundles and can be woven into cloth and ribbons. The short fiber can blow the molten glass into fiber form by hot air or centrifugal force on the turntable. Glass fiber is non-toxic and chemically stable, and is widely used to gradually replace asbestos. But the processability is still inferior to asbestos.
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