Hermetic sealing test specifications define the standardized procedures, equipment parameters, and acceptance criteria used to verify the leak tightness of packaging, enclosures, and sealed components across the pharmaceutical, food, electronics, automotive, and aerospace industries. This technical guide explains the principal test methods, including vacuum decay, pressure decay, bubble emission, helium mass spectrometry, and dye penetration, and maps each method to the applicable ISO, IEC, ASTM, EN, GB, and JIS standards. Read on to learn how to select the correct leak testing protocol, set test parameters, and interpret results with confidence.
Technical Overview
A hermetic sealing test, also referred to as a seal integrity or leak tightness test, is a laboratory procedure that evaluates the ability of a sealed specimen to prevent the exchange of gases or liquids across its seals under an applied pressure differential. The test is a critical quality control step for products whose safety, sterility, shelf life, or operational performance depends directly on the integrity of a closure, weld, gasket, or seam.
Sealing test specifications are generally organized along three dimensions. First, tests are classified as qualitative or quantitative: bubble emission and dye penetration provide a visual pass/fail indication, while vacuum decay and helium mass spectrometry produce a measurable leak rate. Second, tests are classified as destructive or non-destructive: non-destructive methods allow the sample to be returned to production, whereas burst and creep tests deliberately destroy the seal. Third, tests are classified by pressure direction: negative pressure (vacuum) methods draw the specimen outward from the inside, while positive pressure methods pressurize the specimen internally.
The governing framework of specifications is drawn from internationally recognized standards organizations. For flexible packaging, GB/T 15171, ASTM D3078, and JIS Z 0238 define vacuum bubble and pressurization methods. For non-destructive package integrity, ASTM F2338 specifies the vacuum decay method. For medical device packaging, ISO 11607 establishes overall integrity requirements. For electronic and electrotechnical components, IEC 60068-2-17 defines sealing Test Q procedures, while IEC 60529 governs IP-code ingress verification for enclosures. For industrial leak testing, EN 1779 and ASTM E432 provide guidance on method selection, and GB/T 15823 covers helium leak detection technique.
Testing Samples
Flexible Packaging and Laminated Film Samples
This category includes three-side-sealed pouches, four-side-seal sachets, stand-up bags, flow-wrap films, and lidded trays made from laminated plastic, aluminum foil, or paper-plastic composites. Samples are typically tested in the as-produced state, after sterilization or pasteurization, or after transportation simulation, because thermal processing and mechanical stress are the most common causes of seal degradation and micro-channel formation.
Rigid Containers, Closures, and Medical Packaging
This category covers glass and plastic bottles with screw caps, induction-sealed containers, ampoules, vials with elastomer stoppers, prefilled syringes, and blister packs. For sterile medical packaging, samples must meet the microbial barrier and physical integrity requirements of ISO 11607, and testing is performed both on seal areas and on the complete package to detect pinholes, channel leaks, and closure defects.
Hermetically Sealed Electronic Packages
Metal and ceramic electronic packages, such as transistor outline (TO) cans, sensor housings, hermetic relays, and optoelectronic device enclosures, are tested to verify both gross and fine leak behavior according to IEC 60068-2-17. Fine leak testing by helium mass spectrometry is required because moisture ingress through micro-leaks is a leading cause of long-term electronic failure.
Pressure Vessels, Valves, and Piping Components
Valves, fittings, flanged joints, heat exchangers, radiators, fuel tanks, and welded pressure-bearing parts are tested at pressures related to their design conditions. Specifications for these samples typically reference EN 1779 for method selection and require documented leak rate acceptance criteria expressed in units such as Pa·m³/s or mbar·L/s.
Automotive and New Energy Components
Electric vehicle battery packs and modules, fuel cell stacks, cooling plates, drive unit housings, connectors, and cable glands are among the most demanding sealing test samples. These components must demonstrate extremely low leak rates against water and dust ingress, and testing is frequently performed using helium or hydrogen tracer gas methods at accredited third-party laboratories equipped with hard-vacuum chambers.
Testing Items
Depending on the product specification and the applicable standard, a complete sealing test program typically covers the following items:
- Gross leak detection: identification of macroscopic seal defects, pinholes, and channels, typically by bubble emission or vacuum decay.
- Fine leak detection: quantitative measurement of micro-leak rates, typically by helium mass spectrometry with sensitivity down to 10⁻⁹ Pa·m³/s or better.
- Whole-package seal integrity: non-destructive verification of the complete filled package using vacuum decay or pressure decay instrumentation.
- Seal strength characterization: burst pressure and creep resistance of heat seals determined by internal pressurization in accordance with ASTM F1140 and ASTM F2054.
- Channel and pinhole detection: dye penetration testing of porous and non-porous medical packaging per ASTM F1929 and ASTM F3039.
- Ingress protection verification: IP-code testing of enclosures against dust and water jets in accordance with IEC 60529.
Testing Methods
Vacuum Bubble Emission Method (Negative Pressure)
The specimen is fully immersed in a transparent liquid, usually degassed water or a surfactant solution, inside a vacuum chamber. The chamber is evacuated to a specified vacuum level, commonly between 20 kPa and 90 kPa below atmospheric pressure depending on package strength, and held for a defined dwell time, typically 30 seconds. The internal gas expands and escapes through any defect, and a continuous stream of bubbles at a fixed location indicates a leak. GB/T 15171 and ASTM D3078 are the primary specifications for flexible packaging, and the method is classified as destructive when the package is subsequently discarded.
Pressure Decay Method (Positive Pressure)
For products designed to hold internal pressure, the specimen is charged to a specified test pressure, isolated, and monitored for a pressure drop over a set stabilization and measurement period. A decay exceeding the calibrated threshold indicates leakage. For packages, internal pressurization bubble testing per ASTM F2096 inflates the package while submerged and can detect defects as small as approximately 50 micrometers. Burst and creep tests per ASTM F1140 extend this principle to determine the maximum seal strength rather than simple pass or fail.
Non-Destructive Vacuum Decay Method
Specified in ASTM F2338, this method places the sealed package in a test chamber that is rapidly evacuated while highly sensitive transducers monitor the chamber pressure. Pressure rise caused by gas escaping from a leaking package is compared against calibrated reference leaks. The method is instrument-based, quantitative, non-destructive, and suitable for 100 percent in-line or at-line inspection of pharmaceutical and food packages.
Helium Mass Spectrometry Leak Detection
Helium testing, covered by GB/T 15823 and guided by EN 1779, offers the highest sensitivity available for industrial applications. In the hard-vacuum chamber mode, the specimen is charged with helium and placed in an evacuated chamber connected to a mass spectrometer; in the sniffer mode, a probe detects helium escaping from pressurized or bombarded parts. Detection limits reach 10⁻⁹ to 10⁻¹² Pa·m³/s, making the method the reference choice for hermetic electronic packages, EV battery enclosures, and aerospace hardware. Hydrogen-nitrogen mixtures and sulfur hexafluoride tracer gases with dedicated detectors are also used as alternatives where helium recovery is impractical.
Dye Penetration Method
A low-viscosity dye solution is applied to one side of a seal for a specified dwell time, and the opposite side is inspected for dye migration. ASTM F1929 addresses porous materials such as Tyvek-type lid stock, while ASTM F3039 addresses non-porous films. The method confirms through-channel defects with high visual certainty and is widely used for medical packaging validation, although it is destructive and unsuitable for routine lot release.
Environmental and Combined Sealing Tests
For electronic and electrical equipment, IEC 60068-2-17 sealing Test Q procedures immerse components in degassed liquid under vacuum or pressure cycling to force leakage, while IP-code tests per IEC 60529 subject enclosures to dust chambers and water jets, spray nozzles, or immersion tanks. These tests are often sequenced after thermal cycling, vibration, or drop testing to evaluate seal durability under realistic stress conditions.
Applications
Hermetic sealing test specifications support quality assurance and regulatory compliance across a broad range of industries, with typical applications including:
- Pharmaceutical and biological product packaging: sterile barrier verification, container closure integrity, and regulatory submission support per ISO 11607 and ASTM F2338.
- Food and beverage packaging: shelf life assurance for vacuum, modified atmosphere, and retort-processed products per GB/T 15171 and ASTM D3078.
- Medical devices: seal validation of pouches, trays, and combination products, including dye penetration and burst testing.
- Electronics and semiconductors: gross and fine leak qualification of hermetic packages and IP-rated enclosures per IEC 60068-2-17 and IEC 60529.
- Automotive and new energy: leak testing of EV battery packs, fuel systems, cooling circuits, and lighting housings to water and dust ingress requirements.
- Industrial equipment: valves, pressure vessels, piping systems, and welded assemblies tested per EN 1779 method selection guidance.
- Aerospace and instrumentation: high-sensitivity helium leak testing of critical fluid systems and sealed instruments.
FAQ
Question: What is the difference between seal integrity testing and seal strength testing?
Answer: Seal integrity testing determines whether a closed package or component leaks, meaning whether fluids or gases can pass through a defect. Seal strength testing, performed by burst and creep methods such as ASTM F1140, measures the mechanical force or pressure a seal can resist before failing. Both properties are complementary, and complete specifications usually address both.
Question: How do I select the correct vacuum level for the water immersion bubble test?
Answer: The vacuum level is chosen according to the mechanical strength of the package and the expected defect size. Specifications commonly use staged levels such as 20, 30, 50, and 90 kPa with a 30-second hold. Delicate packages and porous materials require lower differentials to avoid false failures from film expansion or natural porosity, while robust packages are tested at higher vacuum for improved detection sensitivity.
Question: What are the typical detection limits of the main methods?
Answer: Visual bubble emission reliably detects defects on the order of tens of micrometers. Instrumented vacuum decay typically resolves holes down to roughly 5 to 10 micrometers depending on package headspace and test parameters. Helium mass spectrometry achieves quantitative sensitivity from 10⁻⁹ down to 10⁻¹² Pa·m³/s, covering fine leak requirements that other methods cannot reach.
Question: Are these tests destructive or non-destructive?
Answer: Bubble emission, dye penetration, and burst or creep tests are destructive. Vacuum decay, pressure decay, and helium chamber tests are non-destructive when performed within rated pressures, allowing tested units to be returned to stock or used for 100 percent inspection.
Question: What leak rate is considered acceptable?
Answer: Acceptance criteria are product specific. Sterile pharmaceutical packaging generally requires no detectable leak through defects larger than a few micrometers. Hermetic electronic packages commonly specify fine leak limits on the order of 1×10⁻⁸ Pa·m³/s. EV battery enclosures are frequently specified in the range of 10⁻³ to 10⁻² Pa·m³/s or tighter using tracer gas methods. The specification must always be derived from the product performance requirement, not from the instrument capability alone.
Question: How should a test program be established for a new product?
Answer: A robust program begins by defining the failure mode to be detected, selects the method using guidance such as EN 1779 and ASTM E432, verifies method suitability with positive controls containing known defects, and then validates repeatability and reproducibility before routine use. Accredited third-party laboratories can support method development, validation, and independent verification to satisfy regulatory and customer requirements.