Micron-level precision
A Precision Guide for Engineers, Researchers & Procurement Officers
Hermetic glass-to-metal feedthroughs are critical components in high-vacuum, high-pressure, and high-voltage environments. Whether used in aerospace sensors, optoelectronic devices, or biotech instrumentation, their design demands precision, material compatibility, and a deep understanding of thermal and mechanical dynamics.
1. Understand the Application Requirements
Before diving into design, define the operating conditions:
- Environment: Vacuum, pressure, temperature extremes, corrosive gases?
- Electrical Needs: Voltage isolation, signal integrity, EMI shielding?
- Mechanical Stress: Vibration, torque, thermal cycling?
These parameters will guide your material selection and sealing method.
2. Choose the Right Glass
The glass must match the thermal expansion of the metal and withstand environmental stress.
| Glass Type | Key Properties | Common Uses |
|---|---|---|
| Borosilicate | Low thermal expansion, chemical resistance | General lab and industrial seals |
| Quartz | High purity, thermal shock resistance | Optoelectronics, high-temp systems |
| Sapphire | Extreme hardness, optical clarity | High-pressure sensors, optics |
| ZnSe | Infrared transparency | IR sensors, laser systems |
3. Match Metal to Glass
Thermal expansion mismatch is the #1 cause of seal failure. Use metals with compatible coefficients:
| Metal | Expansion Coefficient (×10⁻⁶/°C) | Notes |
|---|---|---|
| Kovar | ~5.0 | Ideal for borosilicate; widely used |
| Molybdenum | ~5.2 | High strength, good match for quartz |
| Stainless Steel | ~17.0 | Requires intermediate sealing glass |
| Nickel Alloys | Varies | Used for specialized applications |
4. Design Geometry for Strength & Seal Integrity
- Feedthrough Shape: Cylindrical seals are most stable under pressure.
- Glass Thickness: Thicker glass improves mechanical strength but may reduce flexibility.
- Edge Design: Chamfered or radiused edges reduce stress concentrations.
- Compression vs. Match Seals:
- Compression Seal: Glass is compressed by metal during cooling—strong and reliable.
- Matched Seal: Glass and metal expand at similar rates—used for delicate electronics.
5. Manufacturing Process Overview
- Cleaning: Ultrasonic cleaning of glass and metal to remove contaminants.
- Assembly: Glass is placed inside metal housing with precise alignment.
- Sealing: Furnace or induction heating melts glass to form the seal.
- Annealing: Controlled cooling to relieve internal stresses.
- Testing: Leak testing (helium mass spectrometry), electrical insulation, and mechanical integrity checks.
6. Common Pitfalls to Avoid
- Ignoring Expansion Mismatch: Leads to cracking or leaks.
- Poor Surface Prep: Contaminants weaken the bond.
- Overheating Glass: Causes devitrification and brittleness.
- Skipping Annealing: Trapped stress can cause delayed failure.
7. Partner with Experts
Companies like NDS Technologies specialize in custom glass-to-metal feedthroughs with micron-level tolerances and exotic material capabilities. Collaborating with experienced manufacturers ensures:
- Faster prototyping
- Reliable performance under extreme conditions
- Compliance with industry standards (ISO, ITAR)
Final Thoughts
Designing hermetic glass-to-metal feedthroughs is both an art and a science. With the right materials, geometry, and manufacturing process, you can achieve seals that endure the harshest environments while maintaining electrical and mechanical integrity.
Trusted by Engineers in Aerospace, Biotech, Defense & Energy
At NDS Technologies, we specialize in designing and manufacturing custom hermetic glass-to-metal feedthroughs that perform under extreme conditions. With over 43 years of experience and more than 24,000 custom builds, our components deliver unmatched reliability, precision, and material versatility. Submit a custom quote request today!