A hermetic feedthrough allows electrical power, signals, sensors, gases, fluids, or other energy to pass through a sealed boundary without compromising the integrity of the enclosure.
In vacuum systems, for example, an electrical conductor may need to pass from outside a chamber to an internal electrode while maintaining vacuum tightness and electrical insulation.
This creates a demanding engineering problem.
The feedthrough must simultaneously manage:
- Hermetic sealing
- Electrical insulation
- Mechanical strength
- Thermal expansion
- Temperature
- Pressure differential
- Vacuum compatibility
- Electrical voltage and current
- Chemical environment
- Dimensional tolerances
Ceramic-to-metal feedthroughs are therefore widely used where conventional polymer or glass solutions cannot provide the required combination of electrical, thermal, mechanical, or environmental performance.
High-purity alumina is commonly used as the ceramic insulator, while metals such as Kovar, stainless steel, nickel, copper, nickel-iron alloys, and molybdenum may be selected according to the application. Commercial feedthrough designs also use refractory-metal or active-metal metallization and various brazing systems.
This guide explains the key engineering considerations for designing a hermetic ceramic feedthrough for vacuum, high-voltage, RF, semiconductor, and other demanding applications.
- What Is a Hermetic Feedthrough?
A hermetic feedthrough is a sealed component designed to transfer something through a wall or enclosure while preventing unwanted leakage across the boundary.
Depending on the application, the feedthrough may transfer:
- Electrical power
- Electrical signals
- RF signals
- Sensors
- Thermocouple signals
- Gases
- Fluids
- Optical signals
- Mechanical motion
For electrical applications, a typical ceramic feedthrough contains:
Metal conductor → Ceramic insulator → Ceramic-to-metal seal → Metal housing
The ceramic provides electrical insulation, while the metal structure provides mechanical mounting and connection to the surrounding equipment.
The ceramic-to-metal interface provides the hermetic barrier.
A typical alumina feedthrough may therefore contain:
Alumina ceramic + metallization + braze + Kovar/stainless steel/other metal
- What Does “Hermetic” Mean?
In engineering, hermetic means that a sealed assembly is sufficiently leak-tight for its intended application.
This is particularly important for:
- Vacuum equipment
- Ultra-high vacuum systems
- Hermetic electronic packages
- Semiconductor equipment
- Aerospace systems
- High-voltage equipment
- Sensors
- Medical instruments
- RF systems
A component should not be called simply “hermetic” without defining the applicable leak-testing method and acceptance criteria.
For example, helium mass-spectrometer leak testing is commonly used to evaluate ceramic-to-metal feedthroughs.
Commercial hermetic feedthrough manufacturers commonly specify helium leak testing as part of production inspection; one established industrial supplier, for example, describes 100% helium leak testing for its ceramic-to-metal feedthrough products.
- Basic Structure of a Ceramic Hermetic Feedthrough
A simple electrical feedthrough can be represented as:
Outside
│
Electrical terminal
│
Metal conductor
│
┌──────┴──────┐
│ Alumina │
│ ceramic │
│ insulator │
└──────┬──────┘
Ceramic-
metal seal
│
Metal housing
│
Inside
The exact structure can vary significantly.
Common configurations include:
- Single-pin feedthrough
- Multi-pin feedthrough
- Coaxial feedthrough
- High-current feedthrough
- High-voltage feedthrough
- RF feedthrough
- Thermocouple feedthrough
- Custom instrumentation feedthrough
The basic principle remains the same:
Provide a controlled path through the enclosure while maintaining electrical isolation and hermeticity.
- Why Ceramic Is Used in Hermetic Feedthroughs
Ceramics are particularly attractive for demanding feedthrough applications because they can combine:
- Electrical insulation
- High-temperature capability
- Mechanical rigidity
- Chemical resistance
- Vacuum compatibility
- Dimensional stability
Alumina is one of the most widely used technical ceramics for electrical feedthroughs.
Depending on the application, other ceramics may also be considered, including:
- Aluminum nitride (AlN)
- Beryllium oxide (BeO)
- Zirconia
- Other specialized technical ceramics
The material should be selected according to the actual electrical, thermal, mechanical, and environmental requirements.
- Why Alumina Is Commonly Used
Alumina provides a useful combination of:
- Electrical insulation
- Mechanical strength
- Hardness
- Temperature capability
- Chemical resistance
- Process maturity
- Availability in many grades
High-purity alumina is particularly attractive for demanding vacuum and electrical applications.
However, “alumina” is not a single material specification.
Different grades may have different:
- Al₂O₃ content
- Grain structure
- Porosity
- Dielectric properties
- Mechanical properties
- Thermal expansion
- Surface characteristics
- Metallization behavior
Therefore, the alumina grade should be specified rather than simply writing “ceramic” on an engineering drawing.
- Hermetic Feedthrough Design Starts With the Application
The first question should not be:
“Which ceramic should we use?”
The better question is:
“What must the feedthrough do?”
Start by defining:
Electrical requirements
- Voltage
- Current
- DC or AC
- Frequency
- Insulation resistance
- Dielectric withstand
- RF impedance if applicable
Environmental requirements
- Vacuum level
- Pressure
- Temperature
- Thermal cycling
- Humidity
- Chemical exposure
- Radiation
Mechanical requirements
- Mounting method
- Axial load
- Radial load
- Vibration
- Shock
- Pressure differential
Hermetic requirements
- Required leak rate
- Test method
- Acceptance criteria
Once these requirements are defined, the ceramic, metal, conductor, brazing process, and geometry can be selected.
- Vacuum Feedthrough Design
Vacuum feedthroughs must perform two functions simultaneously:
Transfer electrical or physical energy + maintain vacuum integrity.
Typical applications include:
- Vacuum chambers
- Vacuum furnaces
- Electron microscopes
- Mass spectrometers
- Particle accelerators
- Semiconductor equipment
- Thin-film deposition systems
- Sputtering equipment
- Plasma systems
- Research vacuum systems
For UHV applications, the feedthrough must be evaluated not only for leak tightness but also for:
- Outgassing
- Surface cleanliness
- Materials compatibility
- Bake-out temperature
- Thermal expansion
- Electrical insulation
A hermetic feedthrough used in vacuum service therefore requires more than simply a mechanically strong ceramic-to-metal joint.
- Ultra-High Vacuum Feedthroughs
UHV systems place even greater demands on the feedthrough.
Potential design considerations include:
- Very low helium leak rate
- Low outgassing materials
- Clean ceramic surfaces
- Clean metal surfaces
- Vacuum-compatible brazing
- Controlled processing
- Bake-out compatibility
NASA technical work on hermetic feedthroughs demonstrates the importance of helium leak testing and environmental/thermal qualification for specialized feedthrough designs.
For a UHV project, the customer should therefore specify the complete vacuum requirement rather than simply requesting a “vacuum-tight” feedthrough.
- High-Voltage Feedthrough Design
High-voltage feedthroughs have an additional challenge:
Electrical insulation must be maintained while the conductor passes through a grounded or differently charged enclosure.
Important design parameters include:
- Applied voltage
- Dielectric strength
- Creepage distance
- Clearance
- Ceramic thickness
- Conductor diameter
- Pin spacing
- Surface condition
- Corona behavior
- Edge geometry
For high-voltage systems, increasing ceramic thickness alone does not automatically solve the problem.
The entire electrical field distribution should be considered.
Commercial ceramic feedthrough designs can extend into high-voltage ranges, but the applicable voltage capability is highly dependent on geometry, atmosphere/vacuum, insulation distance, materials, and test conditions.
- Creepage and Clearance
Two concepts are particularly important in electrical feedthrough design.
Clearance
Clearance is the shortest distance through air, vacuum, or another medium between conductive elements.
Creepage
Creepage is the distance along an insulating surface between conductive elements.
Both can affect electrical breakdown.
For high-voltage feedthroughs, designers should consider:
- Pin spacing
- Ceramic surface length
- Ceramic profile
- Conductor geometry
- Metal housing geometry
- Surface contamination
- Operating atmosphere
In vacuum systems, the breakdown behavior may differ significantly from atmospheric conditions.
Therefore, the electrical environment must be included in the design specification.
- Corona and Electrical Field Control
At high voltage, local electric-field concentration can produce corona or partial discharge.
Potential stress-concentration locations include:
- Sharp metal edges
- Small-radius corners
- Pin transitions
- Ceramic-metal interfaces
- Abrupt geometry changes
A feedthrough designed for high voltage may therefore require:
- Rounded conductor transitions
- Controlled ceramic geometry
- Appropriate conductor spacing
- Sufficient creepage
- Corona-free geometry
The ceramic-metal joint should be considered as part of the electrical field design rather than treated only as a mechanical seal.
- Metal Selection for Hermetic Feedthroughs
The metal must be compatible with:
- Ceramic CTE
- Braze alloy
- Operating temperature
- Vacuum environment
- Electrical requirements
- Mechanical requirements
Common options include:
| Metal | Typical reason for consideration |
| Kovar / Ni-Fe-Co alloy | Controlled thermal expansion |
| Stainless steel | Corrosion resistance and structural applications |
| Nickel | Electrical and chemical compatibility |
| Copper | High electrical and thermal conductivity |
| Molybdenum | High-temperature and specialized electrical applications |
| Nickel-iron alloys | Controlled expansion and hermetic packaging |
The final choice depends on the complete assembly.
- CTE Matching
One of the most important design considerations is the coefficient of thermal expansion.
Consider a ceramic bonded to a metal.
During brazing:
Heating → expansion
During cooling:
Cooling → contraction
If the ceramic and metal expand and contract at significantly different rates, residual stress can develop.
A simplified mismatch strain is:
where:
- = metal CTE
- = ceramic CTE
- = temperature change
The actual stress depends on geometry, material stiffness, braze properties, plastic deformation, and constraint.
This is why CTE should be evaluated at the assembly level, not simply by comparing two numbers from material datasheets.
- Ceramic-to-Metal Sealing Structure
A typical alumina hermetic feedthrough may use:
Alumina → Mo-Mn metallization → Ni plating → Braze → Metal
The metallization provides an intermediate surface between the ceramic and the metallic joining system.
The nickel layer can provide a suitable surface for subsequent brazing.
Depending on the design, active metal brazing may also be used.
The choice depends on:
- Alumina purity
- Ceramic geometry
- Metal material
- Required hermeticity
- Operating temperature
- Production requirements
- Mo-Mn Metallization for Feedthroughs
Mo-Mn metallization is widely associated with alumina ceramic-to-metal joining.
A simplified process is:
- Ceramic surface preparation
- Mo-Mn paste application
- High-temperature firing
- Metallization inspection
- Nickel plating
- Brazing to the metal component
- Hermeticity and quality testing
The metallization layer should not be viewed as a simple decorative coating.
It is an engineered interface.
Its adhesion and microstructure can influence:
- Braze wetting
- Mechanical strength
- Thermal cycling
- Hermeticity
- Long-term reliability
- Active Brazing for Ceramic Feedthroughs
Active brazing is another potential joining route.
An active braze alloy contains reactive elements that promote interaction with the ceramic surface.
Titanium is a commonly used active element.
The advantage is that certain ceramic-metal combinations can potentially be joined without a conventional Mo-Mn metallization step.
However, active brazing must be carefully controlled.
Excessive interfacial reactions can produce brittle reaction layers.
Therefore, the process should be evaluated based on:
- Ceramic composition
- Braze composition
- Brazing temperature
- Holding time
- Joint geometry
- Metal material
- Required mechanical and thermal performance
- Single-Pin vs Multi-Pin Feedthroughs
The simplest feedthrough has one conductor.
But industrial systems often require multiple electrical connections.
Examples include:
- 2-pin
- 4-pin
- 8-pin
- 10-pin
- Multi-pin instrumentation feedthroughs
- High-density electrical headers
As the number of conductors increases, the design becomes more complicated.
The designer must consider:
- Pin spacing
- Insulation distance
- Ceramic thickness
- Electrical field distribution
- Thermal expansion
- Brazing process
- Dimensional tolerance
- Connector interface
Commercial multi-pin ceramic feedthroughs may combine high-purity alumina with refractory-metal metallization and Kovar, stainless steel, nickel-iron, copper-based or other conductors.
- RF Feedthrough Design
RF feedthroughs require additional electrical considerations.
The feedthrough can influence:
- Impedance
- Insertion loss
- Return loss
- Resonance
- Signal integrity
- Electromagnetic shielding
For RF applications, the ceramic, conductor, housing, and metallization should be designed as an integrated electromagnetic structure.
The appropriate design therefore depends on:
- Frequency
- Characteristic impedance
- Conductor dimensions
- Ceramic dielectric properties
- Housing geometry
- Connection type
A feedthrough intended for DC power should not automatically be considered suitable for high-frequency RF transmission.
- High-Current Feedthroughs
High-current applications create a different set of requirements.
The main concerns include:
- Conductor cross-section
- Electrical resistance
- Joule heating
- Thermal dissipation
- Ceramic temperature
- Brazed joint strength
- Metal CTE
- Thermal cycling
Copper may be attractive because of its electrical conductivity, while molybdenum and other materials may be considered where temperature or CTE becomes more important.
The conductor should therefore be selected based on the complete thermal-electrical system.
- Thermal Management
A feedthrough is not electrically isolated from thermal effects.
Electrical current produces heat:
where:
- = electrical power loss
- = current
- = electrical resistance
The generated heat must be transferred through the conductor, ceramic, housing, or surrounding structure.
For high-current feedthroughs, the design should therefore consider:
- Conductor resistance
- Contact resistance
- Ceramic thermal conductivity
- Housing thermal conductivity
- Cooling conditions
- Operating temperature
A feedthrough can fail even when its electrical insulation is adequate if thermal stresses become excessive.
- Mechanical Design of the Ceramic Body
Ceramic materials are strong in compression but brittle and sensitive to tensile stress and local defects.
Important geometric considerations include:
- Wall thickness
- Diameter
- Length
- Corner radius
- Chamfer
- Hole diameter
- Pin arrangement
- Mounting interface
Sharp corners should be carefully evaluated because they may concentrate stress.
Machining quality is also important.
A small surface defect can become a crack initiation site under thermal or mechanical loading.
- Brazing and Joint Design
The ceramic-metal joint must be designed to accommodate the brazing process.
Important variables include:
- Joint clearance
- Braze thickness
- Metallization width
- Ceramic wall thickness
- Metal thickness
- Assembly alignment
- Fixture constraint
There is no universal clearance value suitable for every feedthrough.
The optimum range depends on:
- Braze alloy
- Surface condition
- Joint geometry
- Brazing atmosphere
- Component tolerances
- Temperature profile
For production designs, the joint clearance should be part of a validated manufacturing process.
- Vacuum-Compatible Materials
Materials used in a vacuum feedthrough should be evaluated for:
- Outgassing
- Vapor pressure
- Cleanliness
- Thermal stability
- Chemical compatibility
- Bake-out compatibility
Inorganic ceramic and metallic materials are often attractive for demanding vacuum applications because they avoid many of the limitations associated with organic sealing materials.
However, the complete assembly must still be evaluated.
Contamination can originate from:
- Machining
- Plating
- Cleaning
- Brazing
- Handling
- Packaging
Therefore, vacuum compatibility is both a material selection issue and a manufacturing-process issue.
- Hermeticity Testing
Helium leak testing is one of the most important quality-control methods for hermetic feedthroughs.
A typical principle is:
Helium exposure → leak detection → measured helium flow → acceptance decision
The actual test procedure depends on the component and specification.
Potential requirements include:
- Gross leak testing
- Fine leak testing
- Helium mass-spectrometer testing
- Pressure testing
- Vacuum testing
NASA technical documentation describes helium-based leak testing of ceramic seals and feedthroughs and demonstrates the use of thermal cycling before and after leak measurements to evaluate sealing stability.
The acceptance limit must be specified by the customer or application.
- Why 100% Leak Testing Can Matter
For critical hermetic components, sampling inspection may not be sufficient.
A feedthrough may pass dimensional inspection while still containing a microscopic leak path.
Therefore, production programs may require 100% helium leak testing.
This is particularly relevant for:
- Vacuum feedthroughs
- UHV feedthroughs
- Aerospace components
- Semiconductor equipment
- Hermetic electronic packages
- High-value scientific equipment
Some commercial ceramic feedthrough manufacturers explicitly use 100% helium leak testing for production components.
- Thermal Cycling Qualification
Thermal cycling is important because the feedthrough may experience repeated expansion and contraction during service.
A qualification program may include:
Room temperature → high temperature → room temperature → low temperature → room temperature
The exact temperature range and number of cycles should be determined by the application.
After cycling, the feedthrough may be evaluated for:
- Helium leak rate
- Ceramic cracks
- Metallization adhesion
- Braze integrity
- Electrical insulation
- Dimensional changes
NASA testing of ceramic seals has demonstrated the use of repeated thermal cycling combined with leak measurements to evaluate seal stability.
- X-Ray and Cross-Section Inspection
Non-destructive inspection can provide additional information about the joining process.
X-ray inspection may help identify:
- Voids
- Incomplete braze filling
- Component misalignment
- Internal defects
Cross-sectional analysis may be used during process development to evaluate:
- Metallization thickness
- Interface structure
- Braze distribution
- Reaction layers
- Voids
- Cracks
For production programs, the appropriate inspection method should be selected according to the component’s critical characteristics.
- Common Hermetic Feedthrough Failure Modes
Failure Mode 1: Ceramic cracking
Potential causes:
- CTE mismatch
- Thermal shock
- Excessive mechanical constraint
- Sharp corners
- Machining defects
Failure Mode 2: Braze cracking
Potential causes:
- Incorrect joint design
- Excessive residual stress
- Improper braze clearance
- Incompatible materials
Failure Mode 3: Metallization delamination
Potential causes:
- Poor surface preparation
- Incorrect firing conditions
- Ceramic microstructure incompatibility
- Poor metallization adhesion
Failure Mode 4: Helium leakage
Potential causes:
- Ceramic cracks
- Braze voids
- Interface defects
- Metallization defects
- Mechanical damage
Failure Mode 5: Electrical breakdown
Potential causes:
- Insufficient creepage
- Insufficient clearance
- Sharp conductor edges
- Surface contamination
- Inadequate ceramic geometry
Failure Mode 6: Thermal failure
Potential causes:
- Excessive current
- High contact resistance
- Insufficient heat dissipation
- Thermal expansion mismatch
- Hermetic Feedthrough Design Workflow
A practical development workflow can be summarized as:
Step 1 — Define application
Vacuum, pressure, voltage, current, temperature, RF frequency, mechanical load.
↓
Step 2 — Select ceramic
Alumina, AlN, BeO, or another technical ceramic.
↓
Step 3 — Select conductor
Kovar, stainless steel, nickel, copper, molybdenum, or another compatible alloy.
↓
Step 4 — Select joining method
Mo-Mn + Ni + brazing, active brazing, or another validated joining technology.
↓
Step 5 — Design geometry
Ceramic thickness, pin diameter, spacing, joint area, clearance, mounting interface.
↓
Step 6 — Develop process
Metallization, plating, brazing, cleaning, alignment, fixture design.
↓
Step 7 — Prototype
Manufacture initial samples and inspect the joint.
↓
Step 8 — Qualification
Leak, electrical, mechanical, thermal, and environmental testing.
↓
Step 9 — Production
Establish process controls and inspection criteria.
- What Information Should Be Provided for a Custom Feedthrough?
For a custom hermetic feedthrough project, a supplier will normally need information such as:
Application
- Vacuum
- Pressure
- Semiconductor
- RF
- High voltage
- Sensor
- Aerospace
- Industrial equipment
Electrical
- Voltage
- Current
- Frequency
- Number of pins
- Insulation requirement
Environmental
- Minimum temperature
- Maximum temperature
- Thermal cycling
- Vacuum level
- Pressure
- Chemical exposure
Mechanical
- Overall dimensions
- Mounting interface
- Flange type
- Pin dimensions
- Tolerances
Materials
- Preferred ceramic
- Alumina purity
- Metal alloy
- Conductor material
- Plating requirement
Hermeticity
- Required helium leak rate
- Test method
- Acceptance criteria
Quantity
- Prototype quantity
- Pilot quantity
- Annual production volume
The more complete the specification, the easier it is to develop a reliable production process.
- Custom Ceramic Feedthrough Manufacturing
Custom feedthroughs may be developed from:
- Customer drawings
- 3D CAD files
- Existing samples
- Technical specifications
- Application requirements
A complete manufacturing capability may include:
Ceramic forming → machining → metallization → plating → metal fabrication → brazing → cleaning → inspection → helium leak testing
This integrated approach is particularly useful for complex ceramic-to-metal assemblies.
Examples include:
- Single-pin feedthroughs
- Multi-pin headers
- High-voltage feedthroughs
- RF feedthroughs
- Vacuum electrical feedthroughs
- Thermocouple feedthroughs
- Custom ceramic insulators
- Ceramic-to-metal sealing assemblies
- How to Choose a Hermetic Feedthrough Manufacturer
When evaluating a supplier, ask:
- What ceramic materials can you manufacture?
- What alumina purity grades are available?
- Do you provide ceramic machining?
- Can you perform Mo-Mn metallization?
- Can you provide nickel plating?
- Do you offer active brazing?
- Which metals can be joined?
- Can you work with Kovar?
- Can you work with stainless steel?
- Can you join molybdenum or copper conductors?
- What brazing atmosphere is available?
- Can you perform helium leak testing?
- Can you perform electrical testing?
- Can you provide dimensional inspection reports?
- Can you support prototype development?
- Can you support production quantities?
The strongest supplier is not necessarily the one offering the lowest unit price.
For hermetic components, process control, inspection capability, material knowledge, and joining experience can be equally important.
- Hermetic Feedthrough vs Standard Electrical Connector
A standard electrical connector mainly focuses on:
- Electrical connection
- Mechanical connection
- User accessibility
A hermetic feedthrough has a different primary requirement:
The electrical or physical connection must pass through a sealed boundary without compromising the enclosure.
This distinction becomes particularly important in:
- Vacuum systems
- Pressure vessels
- Hermetic packages
- Cryogenic systems
- High-temperature systems
- Semiconductor equipment
A feedthrough is therefore better understood as a system boundary component, not simply an electrical connector.
- Hermetic Feedthrough vs Glass Feedthrough
Both ceramic and glass can be used for hermetic electrical feedthroughs.
The selection depends on:
- Temperature
- Mechanical loading
- Electrical requirements
- Geometry
- Chemical environment
- Thermal expansion
- Manufacturing requirements
Ceramic feedthroughs can be attractive when high mechanical strength, high-temperature performance, electrical insulation, or complex multi-pin structures are required.
The correct choice should be made according to the actual application rather than assuming one material is universally superior.
- Application Examples
Vacuum Equipment
Requirements:
- Vacuum tightness
- Low contamination
- Electrical insulation
- Temperature resistance
Typical components:
- Vacuum electrical feedthroughs
- Multi-pin feedthroughs
- Thermocouple feedthroughs
- High-current feedthroughs
Semiconductor Equipment
Requirements may include:
- Vacuum compatibility
- High temperature
- Electrical isolation
- Plasma/process environment
- Low particle generation
- Dimensional stability
Potential components include:
- Ceramic feedthroughs
- Electrode feedthroughs
- Sensor feedthroughs
- High-voltage feedthroughs
High-Voltage Equipment
Requirements:
- High dielectric strength
- Controlled electrical field
- Adequate creepage
- Adequate clearance
- Hermetic sealing
The ceramic profile and conductor geometry are especially important.
RF and Microwave Equipment
Requirements:
- Controlled impedance
- Low signal loss
- Stable dielectric properties
- Mechanical stability
- Hermetic sealing
The RF feedthrough should be designed as an electromagnetic component rather than only a mechanical seal.
Aerospace and Scientific Equipment
Requirements may include:
- Vacuum
- Thermal cycling
- Vibration
- Shock
- Hermeticity
- Long-term reliability
For these applications, qualification testing is often an important part of product development.
- Practical Design Checklist
Before releasing a hermetic feedthrough drawing, review the following:
Ceramic
- Ceramic grade defined
- Alumina purity defined
- Ceramic dimensions defined
- Wall thickness reviewed
- Surface finish defined
Metal
- Metal alloy defined
- CTE evaluated
- Conductor size defined
- Plating requirement defined
Joining
- Metallization method selected
- Nickel plating considered
- Braze alloy selected
- Joint clearance defined
- Brazing atmosphere defined
Electrical
- Voltage defined
- Current defined
- Frequency defined
- Creepage reviewed
- Clearance reviewed
- Dielectric testing defined
Vacuum / Hermeticity
- Vacuum level defined
- Leak rate defined
- Helium leak test method defined
- Cleaning requirement defined
Reliability
- Thermal cycling defined
- Mechanical testing defined
- Environmental testing defined
- Frequently Asked Questions
What is a hermetic feedthrough?
A hermetic feedthrough allows electrical, signal, fluid, gas, or other energy transfer through a sealed boundary while maintaining the required leak-tightness of the enclosure.
What ceramic is commonly used for hermetic feedthroughs?
Alumina is one of the most widely used ceramics because of its electrical insulation, mechanical properties, temperature capability, and established ceramic-to-metal joining processes.
Can alumina be joined to Kovar?
Yes. Alumina-to-Kovar assemblies can be produced using metallization-based brazing or active brazing processes, depending on the design and application.
What is a vacuum feedthrough?
A vacuum feedthrough is designed to transfer electrical or other functions through a vacuum chamber wall while maintaining the specified vacuum integrity.
How is a hermetic feedthrough tested?
Helium leak testing is commonly used to verify hermeticity. Electrical, dimensional, mechanical, and thermal testing may also be required.
What causes hermetic feedthrough leakage?
Typical causes include ceramic cracks, braze defects, metallization problems, CTE-related stress, contamination, and mechanical damage.
Can feedthroughs be customized?
Yes. Ceramic material, pin number, conductor material, flange configuration, dimensions, metallization, brazing process, electrical specifications, and leak-rate requirements can be customized.
Can a ceramic feedthrough be used for high voltage?
Yes, but high-voltage capability depends on ceramic geometry, insulation distance, conductor arrangement, operating environment, material properties, and qualification testing.
What is the difference between a ceramic feedthrough and a ceramic-to-metal seal?
A ceramic-to-metal seal describes the joining/sealing technology, while a ceramic feedthrough is a functional component that uses such a seal to transfer something through a sealed boundary.
- Conclusion
A hermetic feedthrough is a highly engineered component that combines ceramic insulation, metal construction, joining technology, electrical design, and hermetic sealing.
For demanding applications, successful feedthrough design requires simultaneous consideration of:
- Ceramic material
- Alumina purity
- Metal selection
- CTE compatibility
- Metallization
- Nickel plating
- Braze alloy
- Joint geometry
- Electrical insulation
- Vacuum compatibility
- Thermal cycling
- Helium leak testing
For conventional alumina feedthroughs, Mo-Mn metallization + nickel plating + brazing remains an important manufacturing route. Active brazing can provide another solution for selected ceramic-metal combinations.
The most reliable approach is to develop the ceramic, metal, joining process, geometry, and inspection requirements as one integrated system.
If you are developing a custom vacuum feedthrough, high-voltage ceramic feedthrough, multi-pin feedthrough, RF feedthrough, or ceramic-to-metal hermetic assembly, the project should begin with the application requirements and engineering drawing rather than simply selecting a standard component.