Kovar, an alloy composed primarily of Iron, Nickel, and Cobalt was first patented in the United States in 1936. The specific composition was designed to create a metal with similar thermal expansion characteristics to that of borosilicate glass
The need for a reliable glass to metal seal arose in the design and manufacture of early electrical and electronic devices such as lightbulbs, vacuum tubes, and cathode tubes. Today, Kovar is also used to create hermetic glass to metal sealed microelectronic packages. These packages are used to protectively house the sensitive electronics used in high reliability systems found in the medical, aerospace, telecommunications, and defense industries.
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About Borosilicate Glass
Borosilicate glass is composed of silica and boron trioxide as the main glass-forming constituents.
Borosilicate glass has a low thermal expansion coefficient (~3 × 10−6 K−1 at 20 °C), is chemically resistant and is used for high temperature applications. This is available in many forms and sizes – tubes, rods, plate as well as machined-formed components.
This kind of glass is resistant to thermal shock and is commonly used for reagent bottles. Borosilicate glass plays a great role in many applications from cookware, laboratory equipment, implantable medical devices and space exploration components.
The cookware brands CORNING and PYREX uses borosilicate glass in their production.
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How hermetic glass to metal sealing works
The function of hermetic glass to metal seal in microelectronic packages is to provide a sealed insulator for electrical power and signal channels as well as coaxial RF feedthroughs into and out of the package.
Typically, metals have a greater rate of thermal expansion than that of most glass types. In that case, when the two materials come into contact during thermal cycling the brittle glass will crack. This obviously will not provide a sealed solution.
When Kovar is used in combination with the right type of borosilicate glass the thermal expansion rates are so close that they form what is referred to as a “matched” seal. The two material’s rates of thermal expansion remain similar through a range of temperatures up to and above that of the melting point of the glass. It is during this melting of the glass that the seal is formed.
At the interface between the glass and Kovar, a thin layer of oxide forms. This is what creates the highly robust hermetic glass to metal seal. Packages with this type of glass seal will subsequently remain hermetic through a wide range of temperature cycling.
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Why Hermetic Sealing is Important
In simple terms, hermetic sealing refers to airtight lids that do not allow air or any other material to go in or out of the container or space. The primary purpose of hermetic sealing is to protect components inside these containers from humidity, corrosion and other influences that may damage what is inside the space.
Glass-to-Metal seals are the best form of shield for very sensitive components. Many industries use GTMS ranging from automotive, aviation, medical devices, communications, electric power and military applications.
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AMETEK-ECP has the capability, experience and the solutions to address your needs for hermetically sealed components. AMETEK-ECP uses the highest quality Kovar on the market to provide a reliable and efficient method to bond glass to metal for sealing purposes.