Why Hermetic Sealing Matters

In aerospace, mission-critical, and industrial applications, a switch is not just a switch — it is a potential point of failure. When a limit switch controls a orbital solar array deployment, a flight-critical arming sequence, or a cryogenic valve, the cost of failure is measured in mission loss, not warranty returns.

Standard micro switches rely on plastic housings and elastomeric seals. Under thermal cycling, vacuum, radiation, or corrosive atmospheres, these organic materials degrade. The seal fails. Contaminants enter. The switch becomes unreliable — often without visible warning.

Hermetically sealed micro switches solve this with a fundamentally different approach: all-welded metal shell construction with no organic seals.

How Hermetic Sealing Works

A hermetic seal is a gas-tight enclosure that prevents any exchange between the internal switching chamber and the external environment. In practice, this means:

  • Metal-to-metal welding replaces plastic snap-fits and O-rings
  • Glass-to-metal seals where electrical terminals pass through the shell
  • No venting — the internal atmosphere is permanently sealed at manufacture
  • Leak rate verified by helium mass spectrometer testing

The industry standard acceptance criterion is ≤ 1×10⁻³ Pa·cm³/s — meaning that under a 1-atmosphere pressure differential, less than one cubic centimeter of gas would leak through over 300 years.

Key Specifications Engineers Should Check

When evaluating a hermetically sealed micro switch for your application, these are the essential parameters:

1. Leak Rate

Look for ≤ 1×10⁻³ Pa·cm³/s. This is the GJB 809B-2013 standard for hermetic devices. Anything higher suggests a non-hermetic or “environmentally sealed” device — not the same thing.

2. Temperature Range

Standard industrial switches operate from -40°C to +85°C. Hermetically sealed high-reliability industrial-grade switches can operate from -184°C to +260°C, covering the full range from liquid oxygen to rocket engine compartments.

3. Radiation Hardness

For space and energy applications, Total Ionizing Dose (TID) rating is critical. high-reliability industrial-grade hermetic switches achieve 100 Krad (Si) — sufficient for LEO, MEO, and most GEO missions.

4. Vibration and Shock

Aerospace and mission-critical applications demand survivability under extreme mechanical loads:

  • Sinusoidal vibration: 10~2000 Hz, 15 g
  • Random vibration: 0.04~1.0 g²/Hz ASD
  • Mechanical shock: 100 g, 6 ms

5. Circuit Configuration

SPDT (Single Pole Double Throw) is the most common configuration, offering both N.O. and N.C. outputs from a single device. Dual-switch assemblies provide redundancy for safety-critical circuits.

Applications by Environment

EnvironmentChallengeHermetic Solution
Space vacuumOutgassing, cold weldingWelded metal shell, no organic materials
Cryogenic (-184°C)Thermal contraction, seal failureMetal shell handles differential expansion
RadiationPolymer degradationNo polymers in switching chamber
Salt spray / corrosionContact oxidationHermetic seal blocks all contaminants
High altitudeLow pressure arc-overSealed atmosphere prevents breakdown

Selecting the Right Model

For the KWQM4-4Z series (Postek HK Series), model selection depends on three factors:

  1. Load current: 0.5A (micro-controller) to 5A (power circuits)
  2. AC/DC requirement: Most models are 28V DC; some support 115V AC 400Hz
  3. Temperature range: -65°C (standard) to -184°C (extended cryogenic)

Refer to the complete datasheet for the 8-model electrical ratings table.

Installation Best Practices

Hermetically sealed switches are precision devices. Follow these guidelines:

  1. Mounting: Use M2 screws through Φ2.2 mm holes. Torque ≤ 0.16 N·m. Use mounting washers.
  2. Actuation force: Apply 1.95~40 N perpendicular to the push button axis. Exceeding 40 N can damage the internal mechanism.
  3. Solder temperature: ≤ 350°C for ≤ 3 seconds per terminal.
  4. Matching load: Using a high-current switch for micro-current applications degrades contact reliability over time.

Conclusion

For applications where failure is not an option, the incremental cost of a hermetically sealed micro switch over a standard environmental-seal switch is negligible compared to the cost of mission failure. The all-welded metal shell, verified leak rate, and high-reliability industrial qualification pedigree provide an engineering safety margin that no elastomeric seal can match.

Explore the HK-KWQM4-4Z Series → Product Page | Download Datasheet