Hermetic Glass-to-Metal Sealing

Glass-to-metal seal applications

Glass-to-metal seals are found in a vast array of products and industries, including:

• high-temperature sensors

• oil and gas applications

• batteries and capacitors

• nuclear reactors

• implantable medical devices

• optoelectronic packaging

• automotive airbags

The primary purpose for glass to metal seals is to reliably allow electrical or optical signals to pass through vacuum-tight housings or enclosures. However, these seals also serve the critical function of preventing moisture or gas intrusion and leakage that could cause damage or failure of the encapsulated electrical components and systems, semiconductors, electro-chemicals, pyrotechnics, or other substances.

By performing reliably in harsh operating conditions such as extreme temperatures, moisture, high pressures, or corrosive chemicals, GTMS technology facilitates longevity, performance, and efficiency improvements as well as innovative designs. At their core, these seals provide reliable connection and protection that enables the manufacture of high-quality and long-lasting hermetically sealed components or equipment. The versatility of this technology can be seen in the multitude of functions, designs, and sizes of GTMS components used in a broad range of applications.

Types of GTMS

Hermetic glass-sealed components can be designed in a large variety of formats, sizes, material combinations and complexity.

SCHOTT covers glass-to-metal-sealed products from 1.2 to 600 mm in diameter. Metals range from stainless steel, over aluminum to titanium, copper and more. Our experts know how to choose the right combination of materials from hundreds of different glasses and metals. For example, in case of very high heat dissipation requirements, SCHOTT GTCS® technology enables the design of housings and pins made from copper.

One of the key aspects of creating high-quality glass-to-metal seals is the combination of materials with optimal coefficients of thermal expansion (CTE). The expert selection and subsequent processing of metals and suitable sealing glasses is essential for durable gas-tightness of the seal. GTMS products can be segmented into two types based on the glass and metal selection, and the corresponding CTEs of the chosen materials:


1. Matched seals

The CTE of glass and metal in matched seals is balanced. Matched seals are typically used for applications where high-temperature variations are present, or tight pin pitch or dimensional requirements (for example, miniaturized or non-round shapes) are factors. Depending on the design, matched glass-to-metal seals are able to maintain integrity through tens of thousands of thermal cycles and are well suited for semiconductor and optoelectronic assemblies where structural integrity is essential for precise operation of the enclosed electronics.


2. Compression seals

Due to vastly different CTEs of glass and metal in compression seals, the outer metal eyelet shrinks firmly onto the sealing glass during the production process. This compressive force forms a seal with immense bonded physical strength. In fact, the compressive strength of glass is ten to twenty times higher than its tensile strength. This is why compression seals are typically used for designs with requirements for high mechanical robustness. Usage examples can be found in automotive and energy applications, where long-term seal integrity is essential for continued safe operation of electronics in volatile environments.

Knowing what works

As the pioneer in hermetic glass-to-metal sealing, SCHOTT experts can turn to decades of experience, as well as the most versatile portfolio and in-house know-how, to guide customers in exactly what will work and provide solutions to maximize effectiveness in their application. In a situation where we don’t have a solution in the portfolio yet, we can also explore the possibility to develop it for you.

Glass-to-metal sealing technology

One key aspect of creating high-quality glass-to-metal feedthroughs is combining materials with optimal coefficients of thermal expansion (CTE). The expert selection and subsequent processing of metals and suitable sealing glasses is essential for durable gas-tightness of the seal. GTMS products can be segmented into two types based on the glass and metal used and the ratio of their thermal expansions:

Matched seals

In matched seals, the CTEs of the glass and metal are balanced. This type of seal is typically used for applications where high-temperature variations are present or when tight pin pitch or dimensional requirements are factors (for example, miniaturized or non-round shapes). Depending on the design, matched glass-to-metal seals can maintain integrity through tens of thousands of heating and cooling cycles and are well suited for semiconductor and optoelectronic assemblies where structural integrity is essential for precise operation of the enclosed electronics.

Compression seals

Compression seals use glass and metal with vastly different CTEs. This causes the outer metal eyelet (housing) to shrink firmly onto the sealing glass during the production process. This compressive force forms a seal with immense bonded physical strength. In fact, the compressive strength of glass is 10 to 20 times higher than its tensile strength. This is why compression seals are typically used for designs that require high mechanical robustness. Examples can be found in automotive and energy applications, where long-term seal integrity is essential for continued safe operation of electronics in volatile environments.