The term “hermetically sealed” often implies to being airtight or being impervious to air and gas. When a capacitor is hermetically sealed, the dielectric is encased and forms a pseudo-impervious barrier to protect against water vapor, humidity, chemicals and other foreign bodies. There are three common ways to hermetically seal a capacitor:
Wrap & Foil: The capacitor is wrapped in a tight plastic tape and the ends are filled with epoxy in order to form the seal.
Epoxy Case: The capacitor is encased in a molded plastic shell which is then filled with epoxy.
Metal Hermetically Sealed: The capacitor is encased in a metal can or tube and filled with epoxy.
The rationale behind hermetically sealing a capacitor is to maintain proper functioning and reliability of the component. In the electronics industry, hermetically sealed capacitors can provide benefits to many applications. In some applications, these types of capacitors are vital. Due to a lower incidence of failure, hermetically sealed capacitors are often found in Aerospace, Industrial and Medical applications. Finally, these capacitors provide increased reliability and are able to withstand a more severe environment; including extreme temperatures and humidity.