Glass To Metal Seals Technology

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The function of glass-to-metal seals (GTMS) is to provide a way to hermetically isolate an electrical conductor from one environment to another. Glass is used to form a hermetic barrier and also acts as an insulator between the pin(s) and housing, since glass exhibits superior dielectric (or electrical insulation) properties and very low thermal conductivity . GTMS enable reliable electrical power and/or signal transmission in harsh environments such as high pressure or temperature excursions and/or exposure to corrosive chemicals.

Glass-to-Metal-Seal-Design

There are two basic types of glass-to-metal seals from which to choose: Matched Seals or Compression Seals

Matched Seals

Matched hermetic seals are often used to protect sensitive microelectronic circuitry from temperature excursions and moisture incursion. During the engineering process of a matched seal, housing, pins, and glass components are chosen to have similar Coefficients of Thermal Expansion (CTE) for a range of temperature between ambient and the glass transformation point. A chemical bond between the glass and an oxide formed on the metal components contributes to the strength of a matched seal. Kovar housings and pins, along with borosilicate glass are typically the materials used for matched seals.

 

Matched Seals50 OHM

 

  1. Kovar Pin
  2. Fusite K glass
  3. Kovar Housing
Typical Matched Seal Types:

 

Compression Seals

Compression hermetic seals are very robust by design, and are specified in very harsh environments. When the housing material's thermal expansion rate is higher than that of the glass, a compression seal is created. During the manufacturing process, the housing will contract around the glass upon solidification. This action generates a favorable homogenous radial compression stress on the glass at the glass to metal interface. This engineered expansion mismatch produces a robust seal, which can withstand thermal and mechanical stresses. Compression seals are generally made using steel or stainless steel housings, nickel iron pins, and barium alkali glasses.

Compression SealsCompression-Glass-to-Metal-Seal-Feedthrough

 

  1. 446 Stainless Steel Pin
  2. Fusite T glass
  3. Cold Rolled Steel or Stainless Steel Housing

 

Applications: