Here are some of the pictures of PCB relays I found online. One may notice there are these opening/holes on the top or bottom of the package. What are the purposes of these 'air vents'?
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1 Answer
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There are no openings in the relays as shown, at least not normally. The relays are sealed with epoxy around the joints in the molded plastic housing. What may look like a "vent" most likely is a witness mark from a hot-runner mold where the plastic was injected into each housing part.
The protuberance in the corner(s) is intended to optionally be snipped or sliced off after PCB cleaning in order to vent the relay. This can be of advantage when the external atmosphere is cleaner and less corrosive than what happens inside the relay during its life. If the external environment is potentially worse it maybe better to leave it.
You can find more information in relay application notes. For example, this one from Zettler:
If sealed relays switch heavy loads at high switching rates, increased electrical endurance can be achieved by venting the relay. However, corrosive gases from the ambient atmosphere may penetrate into a vented relay; this can negatively influence the reliability of a relay.
answered Feb 19, 2023 at 2:36