Glass-to-Metal Seals

Glass-to-metal sealing plays an integral role in electronic packaging. As a proven technology, it enables airtight, hermetic packaging for applications where performance, safety, and durability are crucial.

On this page, you will be introduced to glass-to-metal seals (GTMS), their major applications and functions as well as various product types. You can also dive deeper into the technology involved in GTMS and explore the manufacturing process.

As the leading GTMS supplier, SCHOTT’s broad portfolio can meet a wide variety of specific requirements. Explore this page to better understand why SCHOTT has been the partner of choice for customers all over the world for more than 80 years.

Assembly process of a glass-to-metal seal showing the eyelet, pin and glass joining together to form a hermetic bond

Highly robust electrical insulation

Sealing electrical or optical conductors with glass creates a non-permeable seal. As an inorganic material, glass seals do not suffer from aging and are therefore used when sensitive electronic components need to be protected reliably or long-term.

GTMS Glass-to-Metal Sealed Feedthrough Assembly Graphic

Preventing moisture and gas intrusion

Glass as a sealing material creates a hermetic barrier against moisture intrusion, condensation, and leakage, providing more reliable protection in harsh environments than non-hermetic polymer seals. Glass and metal can be directly sealed together without any additional interface materials, reducing complexity compared to ceramic-to-metal seal alternatives.


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 glass-to-metal seals

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

SCHOTT has GTMS products that range from 1.2 to 600 mm in diameter. Metals include stainless steel, aluminum, and titanium. Our experts know how to select the right combination of materials from hundreds of different glasses and metals.

Learn more about the different GTMS product categories.

  Various types of glass-to-metal sealed feedthroughs from SCHOTT.

Glass-to-metal-sealed feedthroughs

Feedthroughs pass power and electrical or optical signals through a barrier or enclosure while also preventing intrusion of dust, moisture, gases, or other elements.

Glass-to-metal sealed connectors in different shapes and sizes.

Glass-to-metal-sealed connectors

Connectors create electrical or mechanical connections between components or systems, allowing cables, wires, or devices to be repeatedly connected or disconnected. They usually consist of a male and female part.

A SCHOTT glass-to-metal sealed pedestal TO header with components.

Glass-to-metal-sealed headers

Headers provide a mechanical base for installing electronic and optical components such as semiconductors, laser diodes, and simple electronic circuits. They come in various pin configurations and can be surface- or through-hole-mounted on a printed circuit board.

A group of glass-to-metal sealed windows and lens caps from SCHOTT.

Glass-to-metal-sealed windows and caps

Windows and lens caps are gas-tight interfaces that allow highly effective and precise sending and receiving of optical signals.

More about windows and caps
Glass-to-metal-sealed microelectronic packages from SCHOTT with different designs.

Glass-to-metal-sealed microelectronic packages

Microelectronic packages protect electrical assemblies and components in ultra-tough operating conditions while enabling reliable power and signal transmission. They are often referred to as hybrid packages, multi-chip module housings, or integrated circuit (IC) packages.

More about packages
A collection of SCHOTT glass-to-metal sealed lids and covers for lithium batteries.

Glass-to-metal-sealed lids

Gastight lids and covers offer durable hermetic protection for lithium primary and industrial-grade lithium-ion batteries. They are also used to close aluminum electrolyte capacitors and ultracapacitors.

More about lids
Technology & Design

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.

Diagram showing a comparison between matched and compression glass-to-metal sealing types
Manufacturing Process

How glass-to-metal seals are produced

Hermetic glass to metal seals are made using a complex but extremely effective production process involving just three components: the metal eyelet (housing), metal pins (feedthroughs), and a glass preform (sealing material). Achieving exceptional reliability of the final assembly requires a thorough understanding of the fundamental details. Competence in various glass types and formulations is key for maximizing robustness and reliability, especially for customized components. For maximum seal integrity, selecting the right metal and glass combination for the application and properly executing the sealing process are critical. SCHOTT’s in-house development capabilities give us the ability to alter or engineer entirely new glass types to solve unique challenges or enable new applications.

The manufacturing of glass-to-metal seals can be broken down into five main areas:

  1. Choosing the right sealing glass

  2. Packaging and feedthrough design and validation

  3. Sealing

  4. Plating

  5. System integration

Production process

Choosing the right sealing glass Choosing the right sealing glass Choosing the right sealing glass Choosing the right sealing glass Choosing the right sealing glass
  • Choosing the right sealing glass
  • Choosing the right sealing glass
  • Choosing the right sealing glass
  • Choosing the right sealing glass
  • Choosing the right sealing glass

Choosing the right sealing glass

As a glass company at heart, glass expertise and manufacturing capabilities are the ‘secret ingredients’ that set SCHOTT apart in glass-to-metal sealing. Glass development, melting, milling, and preform manufacturing are all fully managed in-house by top glass formulation and hermetic sealing experts.

Choosing the right sealing glass based on the metal used and the operating conditions is essential for producing a highly durable glass to metal seal. SCHOTT offers the broadest range of standard glasses and continually develops new specialty glasses that can be used to meet advanced requirements. These capabilities enable us to meet the exact specifications our customers require.

To produce glass preforms, specialty glass melts are processed into shards, milled into fine glass powder, and then pressed and sintered into preforms. SCHOTT glass preforms have an extremely high dimensional accuracy, mechanical stability, consistent weight, and smooth surfaces – all aspects that play a decisive role in enabling robust and reliably hermetic GTMS.

Packaging and feedthrough design and validation Packaging and feedthrough design and validation Packaging and feedthrough design and validation
  • Packaging and feedthrough design and validation
  • Packaging and feedthrough design and validation
  • Packaging and feedthrough design and validation

Packaging and feedthrough design and validation

The development process at SCHOTT is collaborative: We closely work with our customers to deliver the best components for the application at hand.

Direct engineering support, complete customization, and rendering of more cost-efficient or less complex designs are all part of the design and development for glass-to-metal seals. SCHOTT can often improve on the original product concept by drawing on our experience and advanced validation measures.

Validation is key for GTMS. SCHOTT can perform simulations and tests with varying tools and support systems to verify successful implementation in applications and with customer processes. We offer welding, soldering, handling, and various other approaches to demonstrate proof of concept. The bottom line is we take your vision and make it work!



The sealing process transforms the three separate components into a single, vacuum-tight glass-to-metal sealed assembly. To do this, the glass preform, metal eyelet, and metal pins are assembled in a carbon fixture and put through a furnace in a highly controlled and specialized process. The temperature, oven conditions, gas compositions, and heating/cooling behavior of the materials are all expertly optimized to meet assembly requirements.

The end result of a successful glass to metal sealing process is a robust and durable component manufactured according to the exact established design specifications.

Plating Plating
  • Plating
  • Plating


Plating, the final step of producing glass to metal seals, involves applying various surface treatments after the sealing process is complete. These treatments serve various functions such as corrosion protection or enabling electrical interconnection. Plating metals, such as nickel, gold, and zinc, are often applied only to the pins to save precious metal.

SCHOTT performs all plating processes in-house. This is a key differentiating factor in the production process as many GTMS manufacturers outsource this step, leading to longer lead times and potential quality issues.

The internal plating infrastructure at SCHOTT is optimized to enable both prototype quantities as well as high-volume serial production with consistent quality. We can advise on material types and thicknesses to optimize efficiency and performance for the final assembly.

System integration System integration System integration
  • System integration
  • System integration
  • System integration

System integration

After the glass to metal seals pass SCHOTT’s final quality inspection, they are shipped to the customers, who will then install the feedthroughs and connectors into their hermetic assembly.

Customers also equip headers and microelectronic packages with chips or PCBs, for example. Electrode or laser welding is used to bond the wires and close the housing.

The same applies for batteries and capacitors: After they are filled with the electrolyte, the customer welds the SCHOTT lid to the battery or capacitor can.

Customers can integrate the hermetic assemblies into their products themselves or commission a contract manufacturer to do this.

SCHOTT Products & Expertise


Why choose SCHOTT GTMS?

With SCHOTT glass-to-metal seal products, you receive value that goes beyond superior and reliable quality. We work in close cooperation with our customers to develop hermetic components that solve technical challenges. Drawing on decades of experience in glass-to-metal seals, we enable futureproof designs and product optimization that offer differentiation in your markets. As a GTMS expert, SCHOTT offers high-level, customer-oriented service.

A man and a woman collaborating at a table.

We are certified

Certifications for our GTMS production sites cover ISO 9001, ISO 14001, IATF 16949, EHS, AS9100/EN9100/JISQ9100, ISO 5001, ASME, ATEX and IECEx, CE Plus, KTA 1401, and EffiNet.

Reliable design for next-generation products

In partnership with our customers, we continuously develop innovations that improve performance, safety, and durability for mass-produced hermetic assemblies as well as customized products.

Discover some recent application examples below.



A person charging her car.

Reliable connections for electric compressors in EV air conditioners

Optimum sealing and energy transmission in high-voltage applications and 48 V systems allow a better power supply to electric compressors. SCHOTT delivers high quality for high-volume series products.

Read More
The world’s first liquid hydrogen carrier ship: the SUISO Frontier.

World’s first liquefied hydrogen carrier ship features feedthroughs from SCHOTT

The world’s first hydrogen carrier ship – the SUISO Frontier – features numerous glass-sealed Eternaloc® feedthroughs from SCHOTT to provide increased safety. SCHOTT worked with Kawasaki heavy Industries, Ltd. to develop tailor-made double-glass-sealed, vacuum-tight feedthroughs that allow transmission of both electrical and optical signals for the ship´s monitoring systems.

Learn more
Medical professionals perform surgery.

Glass-sealed connectors help increase longevity of medical devices

The electronics inside modern medical appliances need protection from intense conditions such as those in an autoclave. One of the most important components in this process is the connector, which makes electrical and data connections between device sections. These connections are strengthened by the integrity of glass.

Download article

Related products

SCHOTT is the world leader in hermetic glass-to-metal seals (GTMS), serving a wide variety of applications that impact everyday life. Explore our top product offerings below or go to the Product Selector to view all products.

A hand holding an electrical bolt.

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A pair of clothespins on a black wire

When is hermetic really hermetic?

Learn more about hermetic sealing and how it protects sensitive electronics from moisture and gas permeation.

Want to talk directly to an expert?

Let’s discuss how glass-to-metal sealing can be a fit for your application.

Contact us
Christoph Stangl, Head of Business Development
Christoph Stangl

Head of Business Development