Hermetic Glass-to-Metal Seals and Feedthroughs
Complete Hermetics Offers Complete Glass-To-Metal Seals and Feedthroughs
Complete Hermetics uses industry standards to create reliable hermetic glass-to-metal feedthroughs and seals according to the following system:
- Glass is heated to a molten state then wetted to the metal, forming a tight bond.
- The thermal expansion of the glass and the metal si carefully measured and controlled to prevent breakage.
Complete Hermetics offers many options for feedthrus types and standard. Complete Hermetics offers not only electrical feedthroughs, the most common type we make, but also RF and microwave feedthroughs.
Complete Hermetics glass-to-metal seals are very effective in sealing hermetically during severe temperature changes as well as sudden changes in pressure or humidity. When compared to O-ring or epoxy seals, Complete Hermetics glass seals are often more resistant to temperature and pressure changes. Glass seals are also very cost-effective when compared to ceramic seals and may be used in a wider variety of applications. Therefore, Complete Hermetics offers a complete line of glass seal products for a wide variety of uses.
The pin and body assemblies of Complete Hermetics glass-to-metal seals and feedthroughs can be plated for better corrosion resistance, wire bonding and soldering capabilities. Plating options include gold, silver, electrolytic and electroless Ni and tin.
Complete Hermetics also specializes in hermetic seals of titanium terminals, headers and hermetic connectors for medical equipment such as titanium batteries, diagnostic equipment and sensors.
Our experienced engineers will help you with layout and cna recommend sizes, solders and other specifics about your hermetic seals and feedthroughs.
There are two types of glass-to-metal seals; compression seals, in which the materials used have different coefficients of thermal expansion, and matched seals, in which the two materials have similar CTEs
Compressions seals are created when the CTE of the header body or housing greatly exceeds that of the glass or electrodes. In these cases, the outer housing components shrink and mechanically compress against the glass to form a compression seal. Materials used by Complete Hermetics can include:
- Body Materials: Cold rolled steels, Stainless steel, Inconel, etc.
- Glass Materials: Corning 9010/9013 (Alkali Barium), Soda lime, Lead silicate, etc.
- Electrodes Material: Alloy 52, Copper Cored 52 Alloy, Alloy 42, etc.
Typically Compression Seals withstand temperatures ranging from -250°C to 400°C. Allowable operating temperatures would be from -60°C to 200°C under thermal cycling and shock.
When the CTE (Coefficient of thermal expansion) of the body or housing material matches the CTE of the glass or electrode material a matched seal is formed. The hermetic seal is made by forming a bond through wetting and chemical reactions between the glass and metal. Kovar is the most commonly used material for matched seals.
- Body Materials: Kovar, Alloy 42, Tungsten, Molybdneum
- Glass Materials: Corning 7056 (Alkali Borosilicate)
- Electrodes Material: Kovar, Alloy 42, Tungsten, Molybdneum
Typically Matched Seals maximum allowed temperature is limited by the glass material strain point.
Properties of Hermetic Glass-to-metal Seals
The following properties are part of the glass-tometal seals and feedthroughs and are standards for Complete Hermetics products.
Hermetic seal properties:
- Hermeticity: up to 1 x 10-9 atm cc/sec He
- Insulation resistance: typically exceeds 1 GΩ @ 100 VDC
- Mechanical strength can withstand 20,000 psi with proper design for use in high-pressure applications
- Dielectric: can withstand voltage depending on joint geometry and glass material selected. Below are some typical glass values
– Barium Alkali: 6.3
– Brososilicate: 4.9
– Soda Lime: 7.2
Plating and Finishes
Pin and body assemblies can be plated for better corrosion resistance, wire bonding and soldering abilities.
• Gold Plating
• Silver Plating
• Electrolytic and Electroless Ni Plating
• Tin Plating
Complete Hermetics has designed a new process to create high-reliability ceramic glass seals. These feedthrough seals are appropriate for use in hermetic terminals, hermetic connectors and hermetic packages, Depending on the thermal cycle, conventional seals can withstand about 300°C, but these new ceramic seals are rated to withstand temperatures up to 600°C. This ceramic-doped glass process can fabricate seals at a substantially lower cost than the ceramic-to-metal feedthrough process.