What are Hermetic Connectors?

By Amy Goetzman | April 19, 2022

Meet the Connector: Hermetic Connectors

Hermetic connectors are completely sealed against ingress of air or liquid using a glass, ceramic, or composite sealing device or material. Hermetic sealing offers the highest level of protection available against air, gases, chemicals, moisture, debris, and other contaminants. It is an essential feature for many harsh environment connectors, particularly those used in medical, mil/aero, or space applications. 

Connectors that are used in harsh environments where liquids, gases, or other contaminants are present must be completely sealed to protect contacts and materials from exposure to elements that could interfere with the integrity of the connection. Ingress may result in dielectric breakdown or degradation of materials through exposure to elements that result in corrosion or condensation inside of a sealed connection. Hermetically sealed connectors come in all types, including circular, rectangular, RF, fiber optic, and high-power configurations.

Hermetic sealing is also used to separate pressure differentials on two sides of a vacuum. In some cases, hermetic sealing can be achieved as a modular or configurable feature through the addition of a modular seal to a non-hermetically sealed connector. There are three levels of hermetic sealing: fine, high, and ultra-high vacuum, according to IEC 60068. Hermetically sealed connectors are tested to withstand pressures of 10,000 psi and higher while maintaining a stable pressure differential both inside and outside the assembly. 

The term hermetic sealing derives from the ancient Greek figure Hermes Trismegistus, whose writings on alchemy and material properties included a technical procedure in which a mixture of materials was placed in a glass vessel which was completely sealed by fusing the neck closed.  

Hermetic solutions connectors

Hermetic Solutions offers connectors, feedthrough, vacuum products, and headers that can withstand mechanical and thermal stresses that far exceed the limits of most conventional connector solutions.

Common methods for creating a hermetic seal:  

Glass-to-Metal Sealing (GTMS): Glass-to-metal seals combine metal and glass to create a long-lasting vacuum-tight seal. When heated, glass begins to soften or melt; when pressed against metal, it adheres and then hardens, creating an impermeable barrier. “As the parts cool, the shell shrinks at a higher rate than the glass, causing compression and resulting in a fantastically strong seal,” said Tony Gulrajani, Global Product Manager —Hermetics, Airborn. “Hermetic sealing relies on an oxide layer growth caused during the heating cycle and the mismatch of CTEs (Coeffecient of Thermal Expansion) which causes compressive forces.” 

Glass is an excellent insulator and isolates the power so it passes effectively through the pins. In GTMS, the molten glass adheres to the package and pins and insulates the electrical conductors. This is a highly reliable sealing method. In pressure sealing, a preformed glass seal is positioned against a metal connector housing. When pressure is applied during the production process, the metal expands and forms around the glass to create an extremely strong seal.  

The glass firing process entails 2 phases, heating and cooling. During the heating phase, the pins, and shell expand and the glass softens, then in the cooling phase, the metal shrinks on the glass as mentioned earlier,” said Gulrajani. “This compression during cooling allows the connector to be used for higher pressure seals.”

Ceramic-to-metal seals are used in components that must sustain high amounts of pressure, or where high temperatures, high voltages, or chemicals may impact a glass seal. High temperature co-fired ceramics (HTCC) are more stable under these conditions than glass. Both glass and ceramic seals have been tested to well over 1,000 psi.  

Axon Hermax connectors

Axon’ Cable’s HermAx Hermetic Micro-D Connectors are lead-free and RoHS-compliant due to a unique glass-ceramic compound that enables the use of copper alloy contacts. connectors act as pressure or vacuum seals or as a protection against the environment for sensitive equipment. Allowing electrical connection across both sides of a panel, they are typically used where a panel separates two different environments or when an enclosure needs to be isolated from the surrounding area.

O-rings and polymer/epoxy seals are lightweight, inexpensive ways to enhance a physical barrier. These types of seals are not considered true hermetic seals, as they can handle only limited temperature ranges and their materials remain mobile enough to permit some condensation to form inside cavities.     

AMETEK Subsea connector

Ametek’s Subsea Interconnect (ASI) is suitable for extremely harsh environments such as those in the oil & gas industry and deep-sea exploration. This connector is tested to 30,000 psi, 300 °C, and has a 25-year lifespan.

Design Notes  

IP Ratings define various levels of waterproofing for components and are useful for determining a connector’s suitability for exposure to water and other common environmental factors. However, most IP ratings are not sufficient for extreme harsh environment applications, such as space, where a vacuum seal is required, or oil & gas applications, where chemical contaminants are present. IP level 8 indicates hermetic sealing against water in depths of more than one meter. 

Shell materials used in hermetically sealed connectors include stainless steel, aluminum alloy, and titanium, especially for medical applications.  

Conductors can be made from stranded or solid-plated copper and may be insulated. Hermetic connectors may include brass, copper, or nickel iron pin contacts as well as fiber optic cables.   

Amphenol FCI’s glass/epoxy sealed Hermetic Connectors offer a highly reliable electrical connection at both ends serving as a feed through. These connectors/cable assemblies are suitable for high temperature, high pressure applications like gas, water, and energy metering, and medical applications.

Devices made from plastic cannot be hermetically sealed, as polymeric materials possess diffusive and absorbent characteristics with a high permeation conductivity over time, and the process through which a hermetic seal is achieved typically involves high heat, which damages or changes polymeric materials.  

Temperature ranges for hermetic interconnects are wide — typically -100 °C to 200 °C — to enable them to serve in harsh environments.  

Production Hermetically sealed connectors are generally produced in small batches.  

Amphenol Aerospace’s 2M Hermetic Connectors

Amphenol Aerospace’s 2M Hermetic Connectors offer superior sealing in a package that is less than half the size and weight of other 38999 products.

Testing MIL-STD-883 Test Method 1014 is used to determine hermeticity. To be considered hermetic, the internal moisture content or condensation inside a connector must not exceed 5,000 parts per million (PPM) over the lifetime of the device. At 5,000 PPM, the dew point is far below the freezing point, rendering any residual moisture into ice crystals that would not cause corrosion.  

Specifying Guidance This video series from Martec, a Trexon company, offers guidance on how to specify hermetic connectors.

Standards IEC 60068 defines environmental testing of electronic components to assess their ability to perform under extreme environmental conditions.  

Markets, Sectors, and Applications

Equipment for military, space, marine, medical, cryogenics, oil & gas, Test & Measurement, industrial/OEM markets, and other applications that must perform in extreme harsh environments. 


Greene Tweed’s Seal-Connect fiber optic connectors

Greene Tweed’s Seal-Connect fiber optic connectors can be coupled with a permanent bulkhead feedthrough, FC, or ST adapter to create a hermetically sealed connection.


Ametek, Amphenol Aerospace, Amphenol FCI, Amphenol Martec (stocked by Newark), Axon’ Cable, Bel, BTC, Chandler Industries, Fischer Connectors, Glenair (stocked by Powell Electronics), Greene Tweed, Positronic, Radiall, ODU (stocked by Avnet), Sealtron, Souriau (stocked by Interstate Connecting Components [ICC] and Newark), SV MicrowaveTE Connectivity,  Trexon, and others.  

Like this article? Check out our other Meet the Connector, Harsh Environment, fiber optic articles, our Industrial Industry Page, and our 2022 Article Archive

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Amy Goetzman
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