What is the sealing performance of relays?

Refer to the table below to select the appropriate relay for the environment in which it will be used.

Sealing performance (airtightness) of plastic-sealed relay
Sealing performance is tested as airtightness by immersing the relay in highly permeable liquid.
Relays for printed circuit boards have passed A70 and surface mount relays have passed A90.
Using plastic-sealed relays reduces the impact of malignant gas, but does not prevent silicon gas from entering.

Regarding to enclosures for a relay, see Relay Basics: Technology/Enclosures.

Ultrasonic cleaning cannot be used for signal (communication) relays. We recommend cleaning with the immersion or boiling method. For power relays, cleaning with immersion and boiling methods are recommended as well, but some models are available with ultrasonic cleaning. Please refer to the product detail page.