Hermetic sealing is the science and engineering practice of creating a long-term, gas-tight barrier that protects sensitive components from moisture, gases, contaminants, and pressure changes. True hermeticity is often the difference between systems that operate reliably for years and systems that degrade prematurely because the outside environment slowly reaches the components inside.
MPF Products specializes in ceramic-to-metal hermetic technology for feedthroughs, connectors, viewports, and related assemblies used in demanding electronics, aerospace, and vacuum applications. Keep reading to learn how MPF’s advanced materials and testing standards support long-term, gas-tight reliability in systems where failure is expensive, dangerous, or impossible to repair after deployment.
What Is Hermetic Sealing?
Hermetic sealing means more than just “good sealing” or “weatherproofing.” It describes a joint or package whose leak rate is low enough that gas ingress over the component’s lifetime is negligible for its application. In other words, engineers are not relying on O-rings or gaskets alone; they are relying on a combination of metals, glasses, ceramics, and joining processes that create a stable barrier at the microscopic level.
In electronics, hermetic sealing protects semiconductors, hybrids, sensors, and interconnects from moisture and reactive gases that can corrode bond wires, change dielectric properties, or cause shorts. In aerospace, hermetic packages protect mission-critical assemblies from vacuum, thermal cycling, vibration, and radiation, often over service lives measured in years or decades.
In high and ultra-high vacuum systems, hermetic feedthroughs, flanges, and viewports allow power, signals, and optics to cross a vacuum boundary without creating leak paths. That makes hermetic sealing just as important in many vacuum environments as it is in traditional electronics packaging.
Hermetic vs Environmental Sealing
It is important to distinguish hermetic sealing from environmental sealing. Environmental seals are designed to keep out bulk contaminants such as water, dust, or splash exposure under normal operating conditions. Hermetic seals are designed and tested to stop gas ingress at much lower leak rates and over much longer timeframes.
This distinction matters because electronics often fail gradually, not instantly. A connector or package that appears “sealed” can still allow enough moisture or gas diffusion over time to corrode conductors, shift performance, or create latent failures. In harsh environments, that slow degradation is exactly what hermetic sealing is meant to prevent.
The Physics of Leakage
How Gases Find Their Way In
Gas can enter an enclosure through more than visible cracks. Leakage can occur through pinholes, microscopic interface gaps, manufacturing defects, microcracks created by thermal stress, or permeation through less resistant materials. The goal of hermetic design is to eliminate or minimize each of those paths.
Pressure differential also matters. In aerospace, space, and vacuum environments, even tiny imperfections become significant because the driving force pushing gas across a boundary can be large. Over time, molecules take advantage of the weakest available route, which is why seal quality depends as much on process control and material compatibility as on the geometry of the package itself.
Leak Rate as a Design Parameter
Leak rate is the central performance metric in hermetic sealing. It expresses how much gas can pass through a seal over time under a given pressure difference, often in units such as atm·cc/sec or mbar·L/s. In high-reliability electronics and aerospace programs, leak-rate limits are often far stricter than what would be acceptable in conventional industrial sealing.
Because leak rate reflects both design quality and manufacturing quality, it should be treated as a design parameter from the start. Engineers must choose materials, joining methods, and geometries that meet the required leak performance not just on day one, but across years of thermal cycling, storage, transport, and real-world operation.
Core Materials in Hermetic Packages
Metals and Alloys
Hermetic components rely on carefully chosen metals and alloys to create stable interfaces and manage thermal stresses. Stainless steel is widely used in vacuum hardware and housings because of its mechanical strength, corrosion resistance, and weldability. Iron-nickel-cobalt alloys such as Kovar are common in glass-to-metal and ceramic-to-metal seals because their thermal expansion closely matches that of certain glasses and ceramics.
In electronics and aerospace applications, this thermal expansion matching is critical. Assemblies may see large temperature swings, from cryogenic conditions to high bakeout or operating temperatures. If the metal expands or contracts significantly more than the adjoining glass or ceramic, stresses can build up at the interface, leading to microcracks and, eventually, leakage.
Ceramics and Glasses
Technical ceramics such as alumina are widely used in hermetic feedthroughs and packages because they provide strong electrical insulation, high-temperature capability, low outgassing, and excellent stability in harsh environments. They are especially useful where electrical conductors must pass through a sealed wall without compromising vacuum or environmental integrity.
Glass and glass-ceramics are also widely used in hermetic packaging. In glass-to-metal seals, the glass is selected so it bonds to the surrounding metal and maintains a favorable stress state after cooling. This combination makes glass-to-metal sealing valuable for connectors, sensors, windows, and other packages where both electrical insulation and hermeticity are required.
Joining Processes That Enable Hermeticity
Brazing, Active Metal Brazing, and Ceramic Metallization
Brazing is one of the most important joining methods in hermetic sealing. A filler alloy melts below the temperature of the base materials, flows into the joint, and solidifies into a metallurgical bond that blocks gas flow when properly designed and executed.
For ceramic-to-metal assemblies, two common approaches are used: metallization plus brazing, and active metal brazing. In the metallization route – most commonly the moly-manganese (Mo-Mn) process – the ceramic is first given a metallic surface layer, then plated and brazed using conventional filler metals. In active metal brazing, reactive elements such as titanium are included in the braze alloy so the alloy can bond directly to the ceramic surface without a separate metallization step.
These methods are widely used in aerospace, electronics, photonics, and vacuum hardware because they support strong, compact, and highly hermetic joints. The right choice depends on geometry, production volume, material set, and required performance under thermal and mechanical stress.
Glass-to-Metal Sealing
Glass-to-metal sealing is another cornerstone of hermetic packaging, particularly for connectors, headers, and certain types of sensors. The process involves heating a glass preform and metal components so that the glass softens and bonds to the metal surfaces. The behavior upon cooling depends on the design approach: in a matched seal, the glass and metal are chosen for closely compatible coefficients of thermal expansion (CTE) – the Kovar/borosilicate pairing being the classic example – so that differential stress at the interface remains minimal. In a compression seal, the surrounding metal has a deliberately higher CTE than the glass or ceramic it encases, so that as the assembly cools, the metal contracts around the insert and places it in compression. This compressive stress state is mechanically robust and improves leak-rate performance, since ceramics and glasses are far stronger in compression than in tension.
For aerospace and high-reliability electronics, glass-to-metal seals are valued for their stable electrical properties, good high-frequency behavior, and resilience to radiation and harsh environments. The choice of glass composition, metal alloy, geometry, and seal type all influence the resulting stress state and, ultimately, the leak-rate and mechanical performance across temperature extremes.
Welding and Seam Sealing
Welding is used both to create hermetic housings and to attach hermetically sealed subassemblies to larger systems. Techniques such as TIG welding and laser welding can produce fully penetrating welds with low porosity, which is essential for gas-tightness. In electronics, seam welding is often used to close metallic lids on hermetic packages, creating continuous, low-leak joints around the perimeter.
MPF Products has invested in in-house vacuum brazing, welding, and inspection capabilities to maintain control over hermetic joint quality and support custom ceramic-to-metal components for demanding applications.
How Hermeticity Is Tested and Proven
Helium Leak Testing
Helium leak testing is the most common method for verifying hermeticity in electronics and aerospace components. Helium is used because it is chemically inert, present in negligibly low concentrations in ambient air (roughly 5 ppm), and, due to its low molecular weight, it diffuses faster than heavier gases, which makes even minute leak paths detectable. A helium mass spectrometer can measure extremely low leak rates, making it possible to qualify components for demanding and long-life vacuum applications.
In practice, components may be pressurized with helium and then scanned externally (the “sniffer” method), or placed in a helium-filled chamber while a vacuum is drawn inside (the “bombing” or “tracer gas” method). For aerospace and high-reliability electronics, pass/fail criteria are typically governed by MIL-STD-883 Method 1014, with acceptable leak rates defined by package volume and application – though program-specific requirements may impose tighter limits.
Standards and Specifications
High-reliability hermetic components are often qualified against formal standards. In microelectronics and aerospace, MIL-STD-883 Method 1014 is the primary reference for hermetic seal testing, covering both gross-leak and fine-leak procedures, acceptance criteria, and the relationship between allowable leak rate and internal package volume.
Related specifications such as MIL-PRF-38534 and MIL-PRF-38535 govern hybrid and integrated circuit manufacturing more broadly and invoke Method 1014 for hermeticity verification. For space and satellite programs, ECSS standards (European Cooperation for Space Standardization) serve a similar role for the European Space Agency and many commercial space supply chains. In practice, gross-leak testing is performed first to screen for large defects, followed by fine-leak testing with a helium mass spectrometer to quantify residual leak rate against the program’s acceptance threshold.
These standards matter because they create a common language for supplier qualification. Instead of vague claims about quality, engineers can compare test methods, detection thresholds, documentation, and demonstrated leak performance. This is critical when selecting components for systems where repair is difficult and failure is costly.
Why Hermetic Sealing Matters for Electronics
Protecting Sensitive Devices
Modern electronics rely on tiny geometries, high-density interconnects, and materials that can be highly sensitive to moisture, oxygen, and ionic contamination. Even trace amounts of water vapor inside a package can lead to corrosion of bond wires, degradation of dielectrics, and intermittent or permanent failures. Hermetic sealing allows engineers to control the internal atmosphere of a package and keep contaminants out.
This is especially critical in high-value, high-reliability systems such as avionics, satellites, medical implants, and downhole tools. In these environments, a failed component can be extremely costly or even impossible to replace. Hermetic packages help ensure that electronics behave predictably over their intended lifecycle.
Stability Across Temperature and Time
Electronics in aerospace applications often experience wide temperature swings, from launch conditions to space vacuum or high-altitude flight. Hermetically sealed packages are designed to remain stable across these temperature extremes, maintaining internal dryness and pressure to prevent condensation and mechanical stress on the device. This stability is one reason hermetic packages remain indispensable even as polymer and conformal-coating technologies improve.
In addition, hermetic packages mitigate long-term drift caused by environmental factors. By controlling the internal atmosphere, designers can focus on intrinsic device behavior rather than worrying about corrosion or moisture-related degradation over years of operation.
Why Hermetic Sealing Matters for Aerospace & Space Systems
Surviving Vacuum and Thermal Cycling
In space or high-altitude applications, assemblies may operate in hard vacuum while cycling repeatedly between sunlight and shadow, driving large temperature changes. Hermetic seals must withstand these cycles without developing microcracks or losing their gas-tight properties. Materials selection, joint design, and process control are all tuned to minimize differential expansion and manage residual stresses.
Because maintenance and repair are rarely possible in orbit, aerospace programs often specify conservative leak-rate limits and extensive testing before components are integrated into spacecraft or high-reliability subsystems. Hermetic sealing is, therefore, not just an engineering detail; it is a core reliability strategy.
Withstanding Vibration, Shock, and Radiation
Launch vibration, acoustic loads, and mechanical shocks can all put additional strain on sealed packages and feedthroughs. Hermetic seals must be robust enough mechanically to maintain integrity under these loads while still providing tight control over the internal environment. This requirement influences design choices such as wall thickness, joint geometry, and choice of braze or glass systems.
Radiation environments in space can also degrade some polymers and organic materials over time, causing embrittlement, increased outgassing, and eventual loss of sealing integrity. In hermetic designs, reliance on metals, glasses, and ceramics provides better long-term stability against these radiation-induced degradation mechanisms. For many aerospace missions, this material resilience is a key reason hermetic packaging remains the default choice for critical electronics and sensors.
Why Hermetic Sealing Matters for High and Ultra-High Vacuum Systems
Achieving and Maintaining Base Pressure
In high and ultra-high vacuum systems, the consequences of inadequate sealing are immediate and measurable. Every leak path – no matter how small – contributes to the system’s base pressure, and in UHV applications, even a single poorly sealed feedthrough or viewport can prevent a chamber from reaching the pressures required for surface science, particle physics, semiconductor processing, or other vacuum-dependent work. Unlike hermetic packaging for electronics, where the goal is to keep contamination out of a sealed enclosure, UHV sealing is about maintaining an extremely low-pressure environment inside one, and this distinction places exceptional demands on every component that penetrates the chamber wall.
Bakeout, Outgassing, and Long-Term Vacuum Integrity
Reaching and sustaining UHV pressures requires more than leak-tight joints. Chamber systems must be thermally baked out – heated to temperatures typically ranging from 150°C to 450°C – to drive off adsorbed gases from internal surfaces before target pressures can be achieved. Every feedthrough, viewport, and hermetic assembly in the system must survive repeated bakeout cycles without degrading seal integrity, releasing contaminants, or shifting electrical performance. Material selection is therefore as important as joint design: ceramics, refractory metals, and carefully chosen braze alloys are used precisely because they combine low outgassing with the thermal stability that UHV service demands.
Where Hermetic Sealing Is Used
Hermetic sealing is used across many industries wherever electronics, lasers, sensors, or power systems must keep working in the presence of moisture, gases, pressure changes, contamination, or extreme environments. The following examples illustrate what hermetic sealing looks like in real-world applications.
Aerospace
A straightforward aerospace example is a satellite whose computers and sensors are placed inside an airtight metal box so space vacuum, moisture, and contamination cannot damage them while the satellite orbits Earth for years. Hermetic sealing helps preserve performance over long missions where internal conditions must remain stable and system maintenance is impossible.
Oil & Gas
In oil and gas applications, sensors and electronics used in downhole drilling must survive extreme pressure, high temperatures, mechanical shock, and exposure to corrosive drilling fluids, which are all conditions that would quickly overwhelm conventional sealing. Hermetic packages isolate sensitive electronics from that environment, allowing tools to measure formation properties, guide directional drilling, and transmit data reliably throughout a well’s operational life.
Defense
In defense systems, missile guidance electronics enclosed in a hermetically sealed package illustrate the principle clearly: vibration, heat, and moisture cannot get inside and interfere with navigation or control. This is why hermetic packaging is closely associated with rugged military electronics and mission-critical reliability.
Industrial Laser Systems
In high-power industrial laser systems used for cutting, welding, and materials processing, laser modules and beam-delivery optics are often housed in hermetically sealed enclosures with precisely manufactured optical windows or viewports. Hermetic sealing protects both the laser source and the optical path, extending service life and maintaining beam quality in demanding production environments where downtime is costly.
Electronics
In harsh-environment electronics, sensitive chips may be placed in sealed metal or ceramic cans that keep out moisture and dust that would otherwise slowly damage the device. This package-level protection is a major reason hermetic sealing remains important in industrial electronics, controls, and other reliability-driven applications.
Medical Imaging
In medical imaging, detector electronics inside MRI or CT systems can be hermetically sealed so humidity, cleaning chemicals, and environmental contamination do not reach the electronics. That helps maintain clear, reliable imaging performance over many years of operation.
Photonics
In photonics, a laser used for fiber-optic communication may be mounted in a small metal can with a glass window, then hermetically sealed so the laser and optics stay clean, dry, and aligned while light passes out through the window. Hermetic sealing is especially valuable here because even minor contamination or alignment shifts can degrade optical performance.
Quantum Computing
Quantum chips operating at cryogenic temperatures are often placed in hermetically sealed packages so gases and moisture do not leak in and disturb fragile qubit behavior inside a cryogenic refrigerator. In ultra-cold systems, package integrity matters because contamination and outgassing can interfere with stable, repeatable operation.
Semiconductor Manufacturing
In semiconductor manufacturing, electrical feedthroughs on process tools such as CVD systems are hermetically sealed so corrosive gases stay inside the chamber and the surrounding electronics and wafers remain protected. Many of these systems operate at high or ultra-high vacuum, so even small leaks through feedthroughs, ConFlat (CF) flanges, or viewports can affect yield, contamination control, and process stability.
If you are evaluating specific feedthroughs, flanges, or hermetic components for high or ultra-high vacuum systems, see the companion guide on choosing the right vacuum feedthroughs, flanges, and hermetic components for your application.
Design and Selection Considerations
Defining Requirements Early
To design or select hermetic components effectively, engineers should define environmental requirements early in the project. These include external pressure and vacuum conditions, operating and storage temperature ranges, radiation levels, mechanical loads, and desired service life. Also important are electrical requirements – such as voltage, current, impedance, and signal integrity – which influence the choice of feedthrough and connector designs.
For vacuum applications, bakeout compatibility is another requirement to establish early. Components intended for high or ultra-high vacuum systems must survive repeated thermal bakeout – typically at temperatures ranging from 150°C to 450°C – without degrading seal integrity, releasing contaminants, or compromising electrical performance. Not all hermetic components are rated for bakeout, and material choices at the design stage determine whether a feedthrough, viewport, or assembly can meet this requirement.
By clearly specifying these parameters, teams can work with hermetic component suppliers to select standard parts or determine when custom solutions are necessary. Early collaboration helps ensure that materials, geometries, and joining processes align with both performance and manufacturability goals.
Standard vs Custom Hermetic Components
Standard hermetic packages and feedthroughs offer faster lead times and lower design risk when the application fits established dimensions and ratings. Custom components become necessary when the design requires unusual geometries, mixed-material interfaces, extreme environments, or specialized electrical or optical performance.
The key is not whether a part is standard or custom in principle, but whether the final design can achieve the required leak performance, mechanical robustness, and long-term stability in service. In demanding applications, that often depends on the supplier’s ability to control sealing processes, inspect joints, and support application-specific engineering changes.
Bringing It All Together
Hermetic sealing combines physics, materials science, joining technology, and testing discipline into one goal: keeping sensitive systems isolated from the outside world for as long as the application requires. Whether the application is a satellite, a missile guidance package, a quantum chip, a photonics assembly, a medical detector, or a semiconductor process tool, the purpose is the same: protect the critical internals so the system keeps working when ordinary sealing methods would fall short.
MPF Products combines more than 30 years of experience, ceramic-to-metal sealing expertise, in-house manufacturing capabilities, and custom engineering support to help customers solve complex hermetic sealing challenges across electronics, aerospace, vacuum, and other demanding applications. If you are designing a new system, replacing an underperforming hermetic component, or evaluating options for a custom sealed assembly, contact our engineering team to discuss your application and request a quote.