Hermetic sealing is the process of creating an airtight seal. Hermetic sealing can be done with plastics, epoxy resins, glass, metals, ceramics and more. There are many ways to create a hermetic seal, and even more applications. The specifics of what a hermetic seal is and what it’s for depends on the materials, applications, and processes behind it.
What is Hermetic Sealing?
A hermetic seal is simply a watertight and airtight seal. The first hermetic seal was an airtight glass tube known as the Seal of Hermes, which was used in very early alchemy. The process of hermetic sealing was named after the Greek God Hermes and the “hermetic tradition” that gave rise to alchemical experimentation. Though this first seal was made through glass, there are many ways to create an hermetic seal.
What is Hermetic Sealing Used for?
Hermetic seals have many different uses. There are many instances where contact with water or air can damage a delicate connection or stop it from working. Semiconductors, which can be damaged by contact with water or water vapor, are one of the most common. These semiconductors must be carefully sealed to keep them functioning. A hermetic seal might be created by glass, ceramic or metal to protect the semiconductor.
Nearly any device using sensitive electronics, from smartphones to advanced medical equipment to lasers and much more, uses hermetic seals. Circuits, switches, ignitors, sensors, transistors, semiconductors, microchips and much more all require the protection of a hermetic seal to function properly and maintain a long useful life. Hermetic seals are also used to protect electronics in manufacturing equipment, like hermetically sealed load cells. These load cells will maintain their accuracy, last longer, and can withstand cleaning procedures better than those that are not reliably sealed.
There are other types of hermetic seals that you see every day, but probably don’t often think about. A canned food item is an example of a hermetic seal. The can keeps food preserved by preventing contact with the air and therefore stopping bacteria from growing. Some other foods are vacuum sealed with plastic wrapping, which also prevents microbial growth.
There are other hermetic seals around your home that you might not think twice about. Lightbulbs, for example, are hermetically sealed. Many eco-friendly windows are hermetically sealed to reduce the loss of warm or cool air. Your thermostat, multiple components in your car, batteries, your TV, computer, and many other devices all use hermetic seals to function.
How to Make a Hermetic Seal
How a hermetic seal is made depends on the materials being used, and what the seal must be used for. For example, a hermetic seal made with plastic might not be ideal for a device that gets warm, while a glass hermetic seal wouldn’t make sense for a disposable item, like a ready-to-eat meal.
Glass And Metal Seals
Some hermetic seals are created simply by welding metals together. A proper weld prevents moisture and air from entering the seal. However, in some many cases, electrical signals or light still must enter or exit the seal. In these cases, a hermetically sealed glass enclosure might be ideal, or the glass might be soldered to a metal cap, depending on the needs of the object being sealed.
Glass hermetic seals can be made through matched sealed or compression seals, depending on the coefficient of thermal expansion between the metal and the glass. A matched seal is commonly used for lightbulbs, while compression seals are used for objects that must withstand more pressure fluctuations. Glass-to-metal seals can withstand temperatures up to 250 °C (compression seals) and 450°C (matched seals), so they’re useful for applications with high temperature demands. Hermetic seals can also be made using a ceramic-to-metal seal. These types of seals can withstand more demanding environments, but they are more complex to make.
Epoxy And Plastic Seals
Epoxy is another common way to create a hermetic seal. The use of epoxy again depends on the coefficient of thermal expansion between the substrate and the epoxy. Epoxy seals are commonly used in electrical devices and fiber optics. The epoxy can bond to copper, brass, or other epoxy. Epoxy seals can withstand temperatures between 70°C to +125°C or 150°C, so they’re useful for many standard applications, but can’t withstand extreme heat.
Thousands of different types of devices require hermetic sealing to keep them working properly, or to make them work at all. This airtight, waterproof seal is essential to many of the devices that we use everyday, as well as many others that are much more advanced.