Glass-to-metal sealing design

Superior glass-to-metal sealing technology

One key advantage of glass: it is purely inorganic, which means it is non-aging and therefore resilient to mechanical stress, high pressure or temperature cycling. Glass is also resistant against aggressive and potentially corrosive media and can furthermore be sealed directly to metal without any additional welding or soldering.

While a common assumption is, that glass is a fragile material, the careful selection of glass and metal materials actually enables the manufacturing of hermetic seals with superior robustness and reliability.

Did you know that the compressive strength of glass is ten to twenty times higher than its tensile strength? By choosing exterior metal housings with a much higher coefficient of thermal expansion than the glass, the housing shrinks firmly onto the glass during cooling to create a compressive seal. This compressive force improves the feedthrough strength and enables glass-to-metal sealed housings to be used in even the most demanding harsh environment applications.

Thanks to the unique sealing technology, Eternaloc® terminal headers are extremely robust, compression-sealed units that provide practically unlimited pressure-proof hermeticity. Hence, SCHOTT’s glass-to-metal sealing provides the following advantages for Eternaloc® terminal headers:


  • Enhanced safety in cases of accidents

  • Superior resistance against mechanical stress, high pressure, temperature cycling, extreme temperatures

  • Non-aging glass-to-metal seals are maintenance-free, thereby reducing the total cost of ownership


Other sealing technologies that use organic polymers or ceramics can compromise the integrity of the seal and result in leakage and electrical malfunction:

Epoxy seals contain organic substances that age naturally, particularly when exposed to severe temperature fluctuations.

An inorganic alternative is ceramic, but this material cannot be melted directly to metals like steel or copper. Soldering or welding is required that often tends to corrode in harsh environments, starting with surface imperfections that can develop into fissures. Due to the lack of compression sealing, ceramic isolators are also more likely to develop surface cracks over time. Such developments can impair the isolator’s dielectric function and lower the resistance of the seal following an accident. In addition, loss of tightness may occur.