Electronic components used in demanding environments often require more than a conventional plastic or metal enclosure.

Sensitive electronics may need protection from:

• Moisture
• Oxygen
• Contaminants
• Vacuum
• Temperature fluctuations
• Chemical environments
• Mechanical stress

For these applications, hermetic ceramic packages can provide a highly reliable packaging solution.

A typical hermetic ceramic package combines:

Alumina Ceramic

Metallization

Metal Components

Ceramic-to-Metal Brazing

to create a sealed enclosure or interface for sensitive electronic devices.

Hermetic ceramic packaging is particularly relevant to:

• Semiconductor devices
• RF and microwave electronics
• Sensors
• Aerospace electronics
• Medical electronics
• Vacuum electronics
• High-reliability industrial equipment

This article explains the structure, materials, manufacturing process, applications, and design considerations of hermetic ceramic packages.

What Is a Hermetic Ceramic Package?

A hermetic ceramic package is an electronic enclosure designed to prevent the uncontrolled passage of gases and moisture through the package boundary.

Unlike a conventional protective enclosure, a hermetic package relies on a sealed structure to maintain the desired internal environment.

A simplified structure may consist of:

Ceramic Body

↓

Metallized Surface

↓

Metal Frame / Lid

↓

Brazed or Sealed Joint

↓

Electronic Device

The ceramic body provides electrical insulation and structural support, while the metal interface provides a joining and sealing surface.

Why Is Hermetic Packaging Important?

Electronic components can be sensitive to environmental contamination.

Moisture and other contaminants may contribute to:

• Corrosion
• Electrical degradation
• Material degradation
• Reduced reliability
• Performance instability

For high-reliability electronics, controlling the internal package environment can therefore be an important part of the overall system design.

Why Use Alumina Ceramic for Hermetic Packages?

Alumina is widely used for ceramic electronic packaging because it provides a useful combination of:

Electrical Insulation

Alumina can electrically isolate conductors and electronic components.

Mechanical Strength

The ceramic body provides structural support.

Thermal Stability

Alumina can withstand elevated temperatures appropriate to many packaging processes and applications.

Chemical Resistance

Alumina offers good resistance to many chemical environments.

Metallization Compatibility

Selected alumina ceramic surfaces can be metallized to create interfaces for brazing and electrical connection.

This final characteristic is particularly important for ceramic-to-metal packaging.

Metallized Alumina Ceramic in Hermetic Packaging

The ceramic itself cannot normally be directly brazed to metal in the same manner as a conventional metal-to-metal joint.

A metallization layer creates a suitable interface.

A typical structure can be:

Alumina Ceramic

↓

Mo-Mn Metallization

↓

Nickel Plating

↓

Brazing Alloy

↓

Metal Frame

This structure allows the ceramic body to become part of a hermetically sealed metal-ceramic package.

Mo-Mn Metallization

Mo-Mn metallization is a well-established technology for alumina ceramic.

It is commonly associated with:

• Hermetic packages
• Ceramic-to-metal seals
• Electrical feedthroughs
• Vacuum components

The metallization process must be carefully controlled to achieve appropriate adhesion and surface quality.

Nickel Plating

Nickel plating can be applied over the metallized ceramic surface.

The nickel layer may provide:

• Surface protection
• Improved joining compatibility
• Controlled brazing interface
• Improved resistance to handling and processing

The required plating thickness should be defined according to the final application.

Ceramic-to-Metal Sealing

Ceramic-to-metal sealing is one of the most important technologies behind hermetic ceramic packaging.

The process typically involves:

1. Alumina ceramic preparation
2. Ceramic metallization
3. Metallization firing
4. Nickel plating
5. Metal component preparation
6. Brazing
7. Controlled cooling
8. Inspection
9. Hermetic leak testing

The objective is to create a stable interface between ceramic and metal.

Thermal Expansion: A Critical Design Issue

Ceramic and metal materials generally have different coefficients of thermal expansion.

When a package is heated during brazing, the materials expand.

When the package cools, they contract.

If the difference in expansion is not properly managed, stress may develop at the ceramic-to-metal interface.

Potential problems include:

• Ceramic cracking
• Metallization damage
• Brazing failure
• Package deformation
• Hermetic leakage

Therefore, thermal expansion compatibility should be considered during the initial design stage.

Kovar for Hermetic Ceramic Packages

Kovar is commonly considered for selected hermetic ceramic packages because its thermal expansion behavior can be compatible with certain ceramic systems.

Potential applications include:

• Electronic packages
• Ceramic feedthroughs
• Sensor packages
• RF packages
• High-reliability electronics

However, Kovar is not universally appropriate.

The correct metal depends on:

• Ceramic grade
• Package geometry
• Operating temperature
• Brazing alloy
• Mechanical requirements
• Environmental conditions

Hermetic Ceramic Package Manufacturing Process

A typical manufacturing workflow is:

Ceramic Material Selection

↓

Ceramic Forming

↓

Sintering

↓

Precision Machining

↓

Surface Cleaning

↓

Metallization

↓

Firing

↓

Nickel Plating

↓

Metal Preparation

↓

Brazing

↓

Inspection

↓

Hermetic Leak Testing

Step 1: Ceramic Material Selection

The first step is choosing the appropriate alumina ceramic grade.

Possible grades include:

• 95% alumina
• 96% alumina
• 99% alumina

The selection should consider:

• Electrical insulation
• Mechanical properties
• Thermal characteristics
• Chemical environment
• Manufacturing requirements

Step 2: Ceramic Forming and Sintering

The ceramic body is formed into the required geometry and then sintered.

Sintering establishes the ceramic’s final structure and properties.

For precision packages, dimensional control during this stage is important because ceramic shrinkage occurs during sintering.

Step 3: Precision Ceramic Machining

After sintering, additional machining may be required.

Typical operations include:

• Grinding
• Cutting
• Hole machining
• Surface finishing

The machining process determines critical package dimensions.

Step 4: Surface Preparation

The metallization area must be properly cleaned before metallization.

Potential contaminants include:

• Oil
• Dust
• Grease
• Machining residues

Surface preparation is essential for reliable metallization adhesion.

Step 5: Metallization

The specified areas of the ceramic are metallized.

Possible technologies include:

• Mo-Mn metallization
• Tungsten metallization
• Application-specific metallization systems

The metallization pattern can be customized according to the package design.

Step 6: Metallization Firing

The metallized ceramic undergoes controlled firing.

Critical parameters include:

• Temperature
• Time
• Atmosphere
• Heating rate
• Cooling conditions

The objective is to develop a stable bond between the metallization and ceramic.

Step 7: Nickel Plating

Nickel plating can provide the surface required for subsequent joining.

The plating process should control:

• Thickness
• Coverage
• Surface quality
• Adhesion

Step 8: Metal Assembly

The ceramic body may be combined with:

• Kovar frames
• Metal lids
• Metal housings
• Electrical terminals
• Lead pins

The exact configuration depends on the package design.

Step 9: Brazing

The metallized ceramic is joined to the metal component using an appropriate brazing system.

The brazing process must control:

• Temperature
• Atmosphere
• Heating rate
• Holding time
• Cooling rate

The joint design should minimize excessive stress at the ceramic-metal interface.

Step 10: Hermetic Leak Testing

For hermetic packages, leak testing is an important quality-control step.

Helium leak testing may be used to identify leakage through the sealed structure.

Testing requirements should be established according to:

• Customer specifications
• Application requirements
• Applicable industry standards

Applications of Hermetic Ceramic Packages

1. Semiconductor Devices

Semiconductor devices may require packaging that provides:

• Electrical insulation
• Environmental protection
• Thermal stability
• Reliable electrical connections

Potential applications include:

• High-reliability semiconductor packages
• Power semiconductor packaging
• Specialized electronic modules
• Sensor packages

2. RF and Microwave Electronics

RF and microwave devices can require stable packaging structures that maintain electrical and environmental performance.

Potential applications include:

• RF modules
• Microwave devices
• Communication electronics
• Radar-related electronics
• High-frequency packages

The package geometry and metallization configuration can influence electrical performance.

3. Aerospace Electronics

Aerospace electronics can require high reliability and environmental protection.

Hermetic ceramic packages may be used for:

• Sensors
• Electronic modules
• RF components
• High-reliability circuits

The specific qualification requirements depend on the end application.

4. Industrial Sensors

Hermetic packaging can help protect sensitive sensors from environmental exposure.

Potential applications include:

• Pressure sensors
• Temperature sensors
• Vacuum sensors
• Industrial monitoring devices

5. Medical Electronics

Selected medical electronic devices may require reliable environmental protection and electrical isolation.

Ceramic packaging can be considered for specialized sensor and electronic assemblies where hermeticity is required.

Application-specific regulatory and biocompatibility requirements must be evaluated separately.

6. Vacuum Electronics

Vacuum equipment requires reliable sealing between internal and external environments.

Hermetic ceramic packages can be used in:

• Vacuum feedthroughs
• Vacuum sensors
• Scientific instruments
• Specialized electronic equipment

Hermetic Ceramic Package Design Considerations

A successful design should evaluate the entire package rather than the ceramic material alone.

Electrical Requirements

Consider:

• Voltage
• Current
• Insulation resistance
• Dielectric withstand
• Electrical clearance
• Signal requirements

Thermal Requirements

Consider:

• Operating temperature
• Thermal cycling
• Brazing temperature
• Thermal expansion
• Heat dissipation

Mechanical Requirements

Consider:

• Wall thickness
• Dimensions
• Tolerances
• Mechanical loads
• Vibration
• Shock

Environmental Requirements

Consider:

• Moisture
• Vacuum
• Pressure
• Chemical exposure
• Temperature
• Contamination

Hermeticity Requirements

Specify:

• Required leak rate
• Test method
• Test conditions
• Acceptance criteria

Custom Hermetic Ceramic Packages

Many industrial customers require packages that are not available as standard components.

Custom options may include:

• Ceramic dimensions
• Ceramic thickness
• Metallization pattern
• Number of terminals
• Terminal location
• Metal frame
• Metal lid
• Brazing structure
• Plating
• Hermeticity specification

This allows the package to be designed around the customer’s electronic device.

Custom Package Development Process

A typical OEM development process is:

1. Customer Provides Design

The customer can provide:

• 2D drawing
• 3D CAD model
• Existing sample
• Technical specification

2. Engineering Review

The manufacturer evaluates:

• Ceramic geometry
• Metallization
• Metal selection
• Brazing
• Hermeticity

3. Prototype

A small quantity is produced for evaluation.

4. Testing

The prototype can be evaluated for:

• Dimensions
• Electrical performance
• Sealing
• Mechanical assembly

5. Design Confirmation

The design is optimized if necessary.

6. Mass Production

The validated design enters production.

Common Hermetic Package Failure Modes

Ceramic Cracking

May result from:

• Excessive mechanical stress
• Thermal expansion mismatch
• Improper handling
• Poor design

Metallization Delamination

Potential causes include:

• Poor surface preparation
• Incorrect firing conditions
• Contamination
• Process instability

Brazing Defects

Potential causes include:

• Improper brazing temperature
• Incorrect filler metal
• Contamination
• Poor joint design

Hermetic Leakage

Possible causes include:

• Ceramic cracks
• Brazing voids
• Interface defects
• Metallization problems

How to Improve Hermetic Ceramic Package Reliability

A reliable package requires control across the entire manufacturing process.

The most important principle is:

Ceramic, metallization, metal, brazing, and testing should be treated as one integrated system.

Instead of optimizing each process independently, manufacturers should evaluate how the processes interact.

For example:

Ceramic CTE

affects

Metal Selection

which affects

Brazing Stress

which affects

Hermetic Reliability

This systems-level approach is particularly important for high-reliability applications.

Why Work With an Integrated Ceramic Manufacturer?

For OEM customers, an integrated manufacturer can potentially provide:

• Alumina ceramic manufacturing
• Precision ceramic machining
• Metallization
• Nickel plating
• Metal component integration
• Ceramic-to-metal brazing
• Hermetic leak testing
• Dimensional inspection

This can reduce the number of suppliers involved in the project.

Instead of managing:

Ceramic Supplier

Metallization Supplier

Plating Supplier

Brazing Supplier

Testing Supplier

an integrated manufacturer can potentially manage the complete process.

What Information Is Needed for a Hermetic Ceramic Package Quote?

Customers should ideally provide:

Ceramic

• Material grade
• Dimensions
• Tolerances

Metallization

• Metallization type
• Metallization area
• Thickness requirements

Metal

• Metal material
• Frame dimensions
• Terminal specifications

Electrical

• Voltage
• Current
• Frequency

Environmental

• Temperature
• Vacuum
• Pressure
• Chemical exposure

Sealing

• Required leak rate
• Test method

Production

• Prototype quantity
• Annual volume
• Target production quantity

Hermetic Ceramic Package vs. Conventional Electronic Package

The appropriate package technology should always be selected based on the specific device and operating environment.

Frequently Asked Questions

What is a hermetic ceramic package?

A hermetic ceramic package is an electronic package designed to provide a sealed barrier against the uncontrolled passage of gases and moisture.

Why is alumina used in hermetic packages?

Alumina provides electrical insulation, mechanical strength, thermal stability, chemical resistance, and compatibility with selected metallization technologies.

How is ceramic joined to metal?

A typical process uses ceramic metallization followed by plating and brazing to create a ceramic-to-metal joint.

Can alumina ceramic packages be customized?

Yes. Ceramic geometry, metallization patterns, terminals, metal frames, lids, plating, and sealing requirements can be customized.

What metals can be used with alumina ceramic?

Potential materials include Kovar, stainless steel, copper, and nickel alloys. Selection depends on the thermal, mechanical, electrical, and environmental requirements.

How is hermeticity tested?

Helium leak testing is one commonly used method for evaluating hermetic assemblies. The required leak rate depends on the application.

Can hermetic ceramic packages be used for RF applications?

Yes. Ceramic packages can be used in selected RF and microwave applications, although package geometry, dielectric characteristics, metallization, and electrical design must be evaluated together.