What Are Hermetic Seals?
Cinch Connectivity Solutions is diving into hermetic sealing, an innovation with a rich history that is critical to modern technology. It is the process of creating airtight seals that prevent gases, liquids, and solids from passing through.
Though its origins are mythologically linked to the Greek god Hermes, hermetic sealing remains a cornerstone in various industries today. The technology plays a pivotal role in ensuring that electronic systems are protected from environmental factors, particularly in situations where two enclosures need to be isolated while still allowing electrical signals and power to pass between them.
This isolation is often achieved through the use of specially designed connectors that form hermetic seals. Without these seals, moisture, gases, and other contaminants could easily breach the isolation, potentially compromising the system’s integrity.
In extreme environments, such as Chemical Vapor Deposition (CVD) ovens, hermetically sealed connectors are essential. These connectors must block out contaminating gases, withstand extreme temperature fluctuations, and resist intense vibrations, all while maintaining a secure, airtight seal.
Types of Hermetic Seals
Hermetic seals are not one-size-fits-all; they come in various forms, each suited to different applications. The three main types of hermetic seals are glass seals, compression seals, and epoxy seals.
Glass Seals (Matched Seals):
Matched seals are among the most commonly used hermetic seals, favored for their cost-effectiveness and reliability in light-duty applications. In this type, glass is used to create a rigid structure that metal can compress against, forming a seal. The key to a successful matched seal lies in the glass and metal having similar coefficients of thermal expansion, ensuring a durable bond.
Compression Seals:
For more demanding applications, compression seals offer a robust alternative. These seals are designed to handle high-pressure environments, even when the materials involved have differing thermal expansion coefficients. While more expensive and often requiring custom molds, compression seals are indispensable in applications where strength and reliability are paramount.
Epoxy Seals:
Epoxy seals present a versatile and effective method for achieving hermetic sealing. Epoxy bonds well to metals, exhibits high dielectric strength, and provides good thermal conductivity, making it a popular choice for a wide range of applications. The advantages of epoxy seals include:
- Strong Polar Attraction: Epoxy forms a robust bond with metal oxides, preventing the leakage of gases or fluids under various pressure conditions.
- High Dielectric Strength: With the ability to withstand high voltage without breakdown, epoxy enables higher signal density in connectors.
- Good Thermal Conductivity: Epoxy effectively dissipates heat, reducing the risk of overheating and thermal degradation.
- Wide Chemical Resistance: Epoxy is inert to most chemicals, offering superior resistance to corrosion and enhancing the durability of the seal.
Testing and Performance of Hermetic Seals
The effectiveness of a hermetically sealed connector is typically evaluated by its leak rate, which is measured in cubic centimeters per second (cm³/sec). This metric indicates the volume of gas that can pass through a seal over time, with lower leak rates signifying higher performance.
Depending on the application, hermetic seals must meet varying performance standards. For instance, seals used in medical devices may require a longer lifespan and stricter performance criteria compared to those used in industrial equipment.
Connector seal performance is generally categorized as follows:
- Lower Performing Seals: 10-4 cm³/s
- High-Quality Seals: 10-4 cm³/s
- Highest-Performance Seals: 10-12 cm³/s
There are several methods to test leak rates, including:
Pressure Decay Method:
A cost-effective technique for evaluating lower-performance devices. This method involves trapping pressure inside a product and measuring any pressure loss over time.
Mass Spectrometry Method:
Though more expensive, this method provides the most accurate results for high-performance testing. It involves ionizing gases (typically Helium) in a vacuum and measuring the ions’ movement, which correlates with the amount of leakage.
Tracer Gas Method:
This method strikes a balance between cost and accuracy. It measures the concentration of a tracer gas, usually Helium, within an enclosed chamber to assess leakage.
Example Connector Solutions
Hermetically sealed connectors, particularly those utilizing epoxy, offer a cost-effective and efficient solution for many applications. Cinch, a leader in the field, offers a broad range of hermetically sealed connectors, including proprietary epoxy solutions that outperform alternative sealing methods.
Some of the available options from Cinch include:
- Dual Lobe Nano-Miniature Connectors
- Aluminum Weldable Stabilizer Series, RF Feedthroughs
- UHV Vacuum Products
- Micro-D Dura-Con Hermetic Connectors
- Micro-D Connectors with Ceramic Dielectric Material
These connectors, along with other hermetically sealed options, are readily available as off-the-shelf components through distributors like Mouser and Digi-Key. For specialized needs, Cinch also offers custom solutions, enabling the integration of connectors into enclosures tailored to specific applications.
Hermetic Connectors for Rugged Applications
Hermetic seals are available in various forms to meet the diverse demands of different industries. The performance requirements and application environment typically dictate the type of hermetic seal employed. Among the most reliable and widely used are epoxy seals, which can achieve exceptionally low leak rates of around 10-8 cm³/s.
For rapid prototyping and testing, Cinch’s hermetically sealed connectors are accessible as off-the-shelf components. For more challenging applications, custom solutions are available, offering tailored connector designs that meet the most stringent requirements.
