Hermeticity

Hermeticity is the property of a system, container, or enclosure to be airtight, preventing the exchange of gases, moisture, or contaminants with its surroundings. The term derives from hermetic sealing and is used chiefly in engineering, electronics packaging, and vacuum technology. It is not related to Hermeticism, the esoteric philosophical tradition, though the words share a common etymology.

Measurement and testing: Hermeticity is typically quantified by a leak rate, often expressed in units such as mbar·L/s or Pa·m^3/s. Common test methods include helium mass spectrometry leak testing, pressure decay, and vacuum decay. For high-reliability applications, target leak rates can be extremely small, sometimes below 1×10^-9 mbar·L/s, depending on size and service conditions. The specific seal technology—glass-to-metal seals, brazed metal seals, soldered or welded joints, and ceramic packages—affects achievable hermeticity and durability under temperature cycling and vibration.

Applications: In electronics, hermeticity protects moisture and ions that can degrade sensors, MEMS devices, and other miniature components. It is also critical in vacuum systems, cryogenics, optical components, and some medical implants. In packaging, hermetic seals are favored where long-term stability is essential, though many products instead use barrier or semi-hermetic seals with measured MVTR (moisture vapor transmission rate).

Standards and qualification: Hermeticity specifications are defined by industry standards or component datasheets, with testing performed by licensed laboratories. Practical considerations include material compatibility, thermal expansion, and mechanical stresses that may compromise seals during fabrication or service.