Hermetic Seals: Strong but Silent Protection
A transceiver’s hermetic seal may not be apparent but can be vitally important. This airtight seal keeps moisture out, prevents harmful contaminants from penetrating, protects the device from other stresses, such as harsh or pressurized environments or temperature extremes.
Why it’s done
Transceivers or connectors should be protected from exposure to harmful contaminants, such as debris, hazardous gases (like hydrogen), water or water vapor which can damage them.
Hermetic sealing is a requirement in harsh operating environments. The concern is exposing the transceiver to an environment that’s going through extreme temperature changes, particularly in an outdoor installation. A good example of that is telecommunications – in 5G and mobile networks.
Regular gaskets may keep water out, but air contaminants may still get through. A hermetic seal will prevent that. Also, weather conditions can cause moisture condensation on the metal housing. You don’t want that moisture to get into the component.
Dangers of Contamination
Exposure to water droplets, condensed moisture, or water vapor in sensitive optical electronic components like transceivers may not always be visible but condensed moisture inside a transceiver can potentially damage or impede its reliability and performance. Seepage can cause electrical problems, leakage across pins, damage to the silicon chip or circuit board, light scattering across a photonic component due to water droplets at the fiber-to-chip interface, corrosion, and other issues.
Exposure to such stressors may
- damage or shorten the component’s life
- impede performance and reliability
- corrode the transceiver
- or in worst case scenarios, cause the optical component to completely fail.
See this page for examples of hermetically sealed transceivers rated for industrial use at industrial temperatures.
How It’s Done
Sealing is an extra manufacturing process (gasketing) performed in a factory.
Don’t remove the seal.
Hermetic seals are required in highly regulated industries: aerospace/defense, telecommunications or medical.
Testing and Certification
Industrial applications typically require that seals are rigorously tested and comply with industry standards.
Military testing requirements
MIL-STD-883 TM1014 is a universally accepted test to determine a seal’s effectiveness. Other tests include internal water vapor content (MIL-STD-884 TM 1018), optical leak testing (OLT) and residual gas analysis (5000 PPM RGA).
Maximum moisture content permitted inside a hermetic package cannot exceed 5%.
Transceivers for medical uses are typically certified and regulated, as are their hermetical seals.
It may not be specifically stated in product descriptions that a seal has been used. Nevertheless, specific product characteristics suggest the module was sealed when manufactured. Look for descriptors like “can withstand harsh environments,” “can operate in certain (industrial) temperature ranges,” “complies with regulation….”
FYI: Industrial temperature range is -40 degree C to 85 degrees C (or -40 F – 185 degrees F).
Read this article for a detailed explanation of temperature testing of optical transceivers.
Seal Construction, Materials Used
Acceptable materials used for industrial applications are glass, ceramics, and metals.
Quasi or “Near” Hermetic Seal
There are cheaper alternatives. “(True” hermetic seals are costly but spare you malfunctions in the long run). Known as “quasi” or “near-hermetic,” “quasi” seals are typically constructed of polymers that provide low moisture permeability. Materials used include Teflon, epoxy, plastic and/or liquid crystal.
They’re not acceptable for industrial use.
- Hermetic sealing is recommended or required in certain industries and/or for sensitive applications, primarily outdoors where moisture, hazardous gases, debris, and contaminants are a concern. These include military/defense, medical applications and telecommunications;
- Failure to properly insulate and protect a transceiver can result in complete device failure;
- In some industries, hermetic seals must pass rigorous industry-specific tests;
- Hermetic sealing extends the life of transceivers, enhances product capabilities, and improves reliability;
- Hermetic sealing is part of the manufacturing process and typically not visible;
- If you have questions about whether a transceiver is hermetically sealed or suitable for industrial applications, consult with a knowledgeable technical representative. Ask for test data such as compliance and/or intrusion tests, industrial qualifications and/or certifications or temperatures the component can withstand. Order samples. Test the product.
Vitex, based in northern New Jersey, is a fiber optics supplier to US customers serving clients in multiple industries, including telecommunications, aerospace/defense, and medical. Contact us if you have questions on reliability, or temperature testing of optical transceivers.