When is hermetic really hermetic?
Hermetic sealing with glass provides reliable, non-permeable insulation of conductors while enabling electrical power or signal transmission.
Definition of “hermeticity”
The universally accepted test to determine hermeticity is “MIL-STD-883 Test Method 1014.” Historically developed to test safety-relevant microelectronic components in military, aerospace, and class III medical implants, this method is nowadays also widely used as a reliability measure in applications that include automotive airbags, industrial and energy, and even consumer electronics.
To be considered hermetic, the internal moisture content inside a cavity package must not exceed 5000 parts per million (PPM) over the lifetime of the device. At 5000 PPM, the dew point is far below the freezing point, rendering any residual moisture into ice crystals that would not cause corrosion. In comparison: even at relatively dry moisture levels – for example, 8000 parts per million – condensation will form inside the package at a temperature of around 5°C.
Fig 1: Hermetic glass-to-metal seals are designed to keep the moisture content below critical levels over the lifetime of a device.
Polymers and epoxies: high permeation rates and natural aging
While many everyday applications use polymers, epoxies, or PEEK as sealing or packaging materials, they do not offer true hermeticity and must always be considered non-hermetic.
The core downside of these materials is that they are organic in nature, which means they have an inherently high permeation rate. They age naturally over time and will eventually allow moisture to penetrate into a sealed system. This aging process progresses even more quickly under environmental influences such as high temperature, pressure, or chemicals, which can lead to severe leakage issues caused by the sealing materials.
In addition, outgassing during the curing process or during operation can compromise the ambient environment, leading to critical rates of vapor pressure, moisture levels, and condensation.
In practice this means non-hermetic packages are typically used for applications with lower reliability and operational requirements. Hermetically sealed components, on the other hand, can fulfill enhanced needs for longevity, harsh environment reliability, as well as performance and efficiency increases.
Head of Strategic Marketing Electronic Packaging