Hermetic Sealing: Reliable Protection Against Contamination and Unwanted Substance Leakage

Hermetic sealing of packages or components establishes a gas-tight enclosure that prevents mass transfer (especially of gases). It is not the same as IP ratings (dust/water); the required tightness is defined per application via allowable leak-rate limits and is verified and validated using appropriate methods (e.g., helium leak testing). Depending on the use case—e.g., protection from microbes, moisture, dust, or chemical exposure, or preventing leaks/evaporation—proven processes and designs are applied to achieve the specified integrity demonstrably.

Types of Hermetic Sealing in Different Areas of Application

Hermetic sealing ensures product sterility and is an essential part of aseptic filling. At Rommelag, hermetic sealing is an integral element of the Blow-Fill-Seal (BFS) process, which creates a fully enclosed, sterile system free from external contamination. Generally, hermetic sealing is used in the following sectors:

• Food industry
• Electronics
• Industrial plants and mechanical engineering
• Technology and electrical engineering

Legal Requirements

When performing hermetic sealing, the legal requirements applicable to the specific field must be observed. In the sealing of pharmaceutical products, Good Manufacturing Practice (GMP) guidelines apply. For products intended for the U.S. market, FDA regulations must also be met. These guidelines ensure compliance with essential quality standards that protect consumer health.

In BFS packaging, the primary packaging is already tamper-evident; tamper-evident seals typically apply to outer packaging. They are designed to make any prior manipulation immediately visible upon opening. Such seals are usually used as labels, stickers, or security tags.

Hermetic Sealing in Medicine and Pharmaceuticals

Sterile-packaged medicines, medical devices, and implants - such as pacemakers and artificial joints - are protected from contamination within hermetically sealed packaging. They can be stored safely until their expiration date, ensuring there is no risk of infection during use. Hospitals, clinics, emergency services, and healthcare professionals place great trust in the sterile filling and sealing technology of the Blow-Fill-Seal (BFS) process. The BFS system, through its fully automated process, minimizes contamination risks to a negligible level.

Airtight Packaging for Cosmetics

Many consumers prefer cosmetics without preservatives. To ensure that such products maintain their quality until first use, hermetic sealing is highly recommended.

Vacuum Packaging, Jars, and Cans

Perishable foods, such as meat and cold cuts, stay fresh longer when stored in airtight, vacuum packaging. When jars and cans are hermetically sealed, neither air, moisture, nor bacteria can penetrate. This ensures long shelf life for preserved fruits and vegetables, fruit purées, jams, and similar products.

Hermetic Sealing in Electronics

In electronics, hermetic sealing has proven highly effective for protecting sensitive functional parts such as memory chips. Electronic components, such as sensors, batteries, and connectors, are safely enclosed in hermetically sealed housings, shielding them from damaging environmental influences.

Application of the Process in Industry and Mechanical Engineering

In industrial and mechanical engineering, components are hermetically sealed to prevent the leakage of liquids, gases, or oils. Hermetic housings are ideal for sealing pumps, valves, and gear systems, ensuring secure operation and reducing maintenance costs.

Hermetic Sealing in Technical Systems and Components

Hermetic sealing in technical equipment and components ensures a gas-tight enclosure. It is typically achieved by metallurgical joints such as welding or brazing, as well as glass/ceramic-to-metal seals and hermetic feedthroughs. Elastomeric seals (e.g., O-rings) are only partly suitable because they are diffusion-permeable. The required tightness is application-specific, defined via leak-rate limits (e.g., He-leak), validated, and—depending on risk—monitored in service. 

Not to be confused with IP ratings (dust/water): Hermeticity refers to gas-tightness and is verified separately via leak-rate specifications.

Methods of Hermetic Sealing

Depending on the products or technical components that require protection, various hermetic sealing methods can be applied. The most common techniques include:

• Welding
• Soldering
• Bonding with resins
• Glass-to-metal or ceramic-to-metal sealing
• Laser, resistance, or ultrasonic welding

Laser, resistance, or ultrasonic welding

Laser and resistance welding heat the material to the melting point. Ultrasonic welding, in contrast, generates localized frictional heat at the joint and is considered a low-thermal-load process overall.

Soldering for secure closure of metal housings

Soldering is a proven technique for metal housings and glass-to-metal joints. It creates strong, nearly impermeable bonds that effectively prevent the passage of gases and liquids.

Bonding with special resins or adhesives

Adhesives and resins can provide sealing, but true hermeticity typically requires glass/ceramic-to-metal seals or specifically validated epoxy-based hermetic designs.

In electronics, resin sealing is used to protect LED modules from environmental damage. Specialized adhesives effectively seal components made of plastic, metal, ceramic, and glass against material exchange.

Glass-to-metal or ceramic-to-metal feedthroughs

In the packaging of electronic components, glass-to-metal sealing plays an essential role. By soldering or welding, solid ceramic-to-metal joints can be created for hermetic encapsulation.

Hermetic Sealing in Pharmaceutical Packaging

Hermetic sealing is particularly crucial for pharmaceutical products, where sterility and product quality are top priorities. These factors are indispensable for safeguarding patient health. The standards governing pharmaceutical packaging integrity are therefore subject to legal regulation.

For sterile medicinal products, EU-GMP Annex 1 defines container-closure integrity (CCI) expectations and validation of deterministic test methods (e.g., USP <1207>). National competent authorities conduct inspections, while the EMA coordinates guidance and inspection networks. For the U.S. market, 21 CFR 211.94 also applies.

Sealing Pharmaceutical Primary Packaging

Primary packaging refers to containers that come into direct contact with medical products. The most common types include:

• Blister packs for tablets and capsules
• Glass or plastic bottles for liquid medicines
• Plastic ampoules or containers (e.g., LDPE) manufactured using the BFS process
• Bags and tubes

In the BFS process, sealing occurs thermally immediately after filling within the same mold, without the need for a separate welding or laser station.

Selected Methods for Sealing Pharmaceutical Products

In addition to BFS, various sealing methods are employed, including heat sealing, flame or laser sealing, induction sealing, and adhesive sealing, each of which is applied in different industries.

Heat Sealing

Packaging made from combinations of plastic and aluminum is effectively protected against contamination through heat sealing. During this process, the edges of thermoplastic films are fused together using heat and pressure.

Flame, crimp, and laser sealing (ampoules & vials)

Glass ampoules are hermetically sealed immediately after filling by flame sealing (tip/pull seal); the glass-to-glass fusion forms a gas-tight seal. 

Glass vials, on the other hand, are sealed with an elastomer stopper and crimped with an aluminum cap; the seal is created by the coordinated system of vial neck, stopper, and crimp and must be validated by means of CCI tests. A flip-off or protective cap primarily serves as tamper protection, reducing contamination risks on the outside, but it is not part of the hermetic seal. Laser sealing can offer advantages for suitable plastic or composite systems (clean, locally limited), but requires laser-transparent materials and an appropriate design. 

Vial integrity must be verified via CCI testing (e.g., per USP <1207>); for glass ampoules, flame sealing remains the standard.

Induction Sealing

Induction sealing is ideal for closing bottles containing liquid medicines, such as cough syrups. When the aluminum foil closure is heated by electromagnetic induction, it bonds firmly to the neck of the bottle.

Adhesive Sealing with Sealants

In pharmaceutical use, approved sealants are applied selectively (e.g., device/component interfaces). For primary containers, adhesive bonding is rarely a hermetic closure; CCI requirements are predominantly met by flame/thermal sealing, crimped closures, or validated welding processes.