Glass-to-Metal Sealing Technology (GTMS)


Glass-to-metal seals (GTMS) and ceramic-to-metal seals (CerTMS®) are vacuum-tight assemblies of glasses and ceramics with metals, and are used to feed electrical conductors through the walls of hermetically sealed packages.

A typical GTMS consists of an external metal part into which a pre-formed sintered glass element is sealed. The sintered glass element, in turn, encloses one or more metal leads that are sealed into it. Because of the different expansion coefficients of various glasses and metals, mechanical stresses during the melting process are inevitable. By adopting special design principles it is possible to obtain GTMS in which these stresses do not result in a weakening of the structure but, on the contrary, are used to obtain particularly stable devices.

GTMS Types

Our GTMS products can be broadly divided into two types, matched seals and compression seals.
  • Matched Seals

    The matched seal type is designed to seal Fe-Ni-Co alloy (Fe: 54%, Ni: 28%, Co: 18%), known as Kovar (KV for short), with glass. The thermal expansion coefficient of Kovar synchronizes with that of glass over a wide range of temperatures.

    The matched seal type can be used to make a variety of terminals with comparatively few restrictions on the terminal shape. At the same time, it provides high air-tightness and electrical insulation.

    Base: Kovar
    Lead: Kovar
    Glass: Borosilicate glass (categorized as hard glass)

  • Compression Seal

    The compression seal is designed to exert concentric compressive stress on the glass in the available temperature range, while considering the thermal expansion coefficients of the metal and glass.

    In general, there are three different types of compression seals, namely seals with steel or stainless steel housings, iron seals and #42-alloy seals.

For more information regarding our GTMS/SCHOTT CerTMS® products, please download our catalog from our download page.

Advantages of the Technology
  • Effective hermeticity
  • Resistance in harsh environments e.g. against corrosive materials, vibrations, serious temperature fluctuations
  • Long-term, reliable protection of the packaged component


They have proven successful in electronic and electrical engineering and cover a wide range of applications in which the sealing glass serves as an excellent insulator.
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