Glass-to-Metal Seal Design Guide

Find the right design for your hermetic application.

Glass-to-metal sealing is used is to create robust electrical feedthroughs into a vacuum-tight package. This can be accomplished with two different mechanisms: Compression sealing and matched sealing.

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About the product

About the sector
pressure sensor glass feedthrough

Compression Seals

Compression seals employ a coefficient of thermal expansion mismatch between glass, housing and pins. The hermetic seal is established because the thermal compression of the outer housing acts on the glass as the parts cool down after heat treatment. Housing materials with a high CTE, such as stainless steels or titanium are well suited for compression seals. Depending on design, a compression seal can withstand a very high level of pressure (up to 3000 bars possible). This type of glass-to-metal seal is, among other uses, perfectly suited for high-pressure sensors.

Matched Seals

In a matched glass-to-metal seal, the coefficient of thermal expansion of glass, housing and pins are matched as closely as possible. Matched seals have the advantage that only small levels of residual stress are present and the feedthrough can withstand very high temperatures. The seal between glass and metal is mainly established chemically through an oxide layer. Typically, Kovar is used as a housing material for matched seals. This type of glass-to-metal seal is often used for hermetic electronics packages.

Glass-ceramics-to-metal seals

Glass-ceramics feedthroughs are matched seals which can used for high performance applications. The glass-ceramic material has amorphous and crystalline phases and is produced through controlled crystallization during the sealing process. Glass-ceramics seals have many advantages over conventional seals: They can be matched to many types of metals, can sustain temperatures up to 700 °C and are even more chemically robust. Using glass-ceramics seals, we can manufacture feedthroughs with copper conductors and stainless-steel housings.

Compression SealMatched Seal
Sealing principleThermal compression between glass and housingChemical bonding at the interfaces
Typical housing materialsCarbon steels, various stainless steels, Titanium, Inconel, Hastelloy, etc.Kovar, alloy 42, Molybdenum, etc.
Typical pin materialsNiFe47 / alloy 52, Inconel, copper-core alloy 52, Kovar, Molybdenum, etc.Kovar, alloy 42, Molybdenum, etc.
Typical glass materialsBarium oxide, Soda-lime, Aluminoborate, Borosilicate, etc.Borosilicate
Special propertiesHigh bust pressure capability, very robust, chemically very inertVery high temperature capability, stress-free design
ApplicationsSensor-housingshermetic connectorssight glassespower feedthroughsElectronics packages

Example material combinations for compression seals:

Stainless steel housing – Barium alkali glass – Nife47 / alloy 52 pins: For small-signal sensor feedthroughs and hermetic seal connectors

Carbon steel housing – Barium alkali glass – Carbon steel pin: For high-power terminal plates

Carbon steel / stainless steel housing – Soda-lime glass: For sight glasses

Example material combination for matched seal:

Kovar housing – Borosilicate glass – Kovar pins: For RF electronics packages

Brazing materials

Brazing can be combined with the glass-to-metal sealing process. This is often used to attach an additional component that does not need to be electrically insulated (e.g. adding a filling tube to pressure sensor housing).

Common brazing materials that can be used alongside glass sealing:

Ag-Cu-Pd: Various compositions for brazing temperatures of 800 to 1000 °C.

Au-Ni: For brazing at around 950 °C.

Surface treatment options

Various surface treatment options exist, which are typically performed after the sealing process. They serve the purpose of either corrosion protection or to enable the electrical interconnection. For small-signal feedthroughs, the plating is often only performed selectively on the pin to save precious metal.

Common surface treatment options include:

Nickel + soft gold: For wire-bondable and solderable pins

Nickel + hard gold: For connector pins (also solderable)

Nickel: Corrosion protection

Zinc + thick-film passivation: Corrosion protection

Specifying your custom design

We are here to assist you with finding the right design for your hermetic application. Please do not hesitate to contact us with your requirements or general design idea. Here are some tips on specifying your requirements:

  1. Housing geometry and material boundaries
  2. Feedthrough requirements (number of conductors, arrangement)
  3. Environmental requirements (pressures, temperatures, hermeticity, chemical durability)
  4. Electrical requirements (current carrying capacity, electrical insulation)
  5. How will your feedthrough be attached?
  6. What special functionality do you need?

Our Products and Services

The Dietze Group helps its customers with custom interconnection solutions from concept to series production. Our products are designed in close collaboration with our customers and engineered to meet the application’s specific needs.

Glass-to-Metal Seals

Glass-to-metal feedthroughs provide electrical connections into hermetic packages, even under extreme conditions.

Connector Pins & Stamping

High-precision terminal pins and stamping parts guarantee reliable electrical connections in demanding applications.

Lead-in Wires

Welded leadwires provide the interconnection for light sources and special-purpose electronic applications.

Industries served: Automotive, Aerospace & Military, Electronics, Lighting, Energy, Refrigeration