Author: Postek Engineering Team | Reading time: 10 minutes
Introduction
“Sealed” is one of the most misused terms in component specification. Engineers frequently specify “IP67 rated” switches assuming they are protected against all environmental threats — only to discover that at 50,000 feet, their “sealed” switch has failed because the internal atmosphere equalized with near-vacuum external conditions.
This article clarifies the fundamental differences between environmental sealing (IP ratings) and true hermetic sealing, and provides clear decision criteria for when each is appropriate.
The Problem: IP Ratings Don’t Mean Gas-Tight
What IP67 Actually Means
The IP (Ingress Protection) rating system, defined by IEC 60529, measures protection against solid objects and liquids:
- IP6X: Dust-tight — no ingress of dust. Tested with talcum powder in a vacuum chamber for 8 hours.
- IPX7: Protected against temporary immersion — 30 minutes at 1 meter water depth.
What IP67 does NOT measure:
- Gas or vapor transmission
- Performance under pressure differential
- Long-term seal degradation
- Outgassing of seal materials
The Altitude Problem
As altitude increases, atmospheric pressure decreases:
| Altitude | Pressure | Effect on IP67 Seal |
|---|---|---|
| Sea level | 101.3 kPa | Normal operation |
| 30,000 ft (9,144m) | 30.1 kPa | Seal under stress — differential pressure begins |
| 50,000 ft (15,240m) | 11.6 kPa | IP67 seals can leak as internal pressure vents |
| 65,000 ft (19,812m) | 5.5 kPa | Near-vacuum — IP67 seals will fail |
| Space (>100km) | <0.001 kPa | Hard vacuum — only hermetic seals survive |
At 50,000 feet, the external pressure (11.6 kPa) is approximately 11.5% of sea level. A switch sealed at sea level has an internal pressure of ~101 kPa pushing outward. If the seal is not gas-tight, the internal atmosphere will vent — carrying moisture and contaminants through the switch interior. When the aircraft descends, external pressure increases and forces new (potentially moisture-laden) air back inside.
Technical Background: What Makes a Seal “Hermetic”?
The Leak Rate Standard
Hermetic sealing is defined by a maximum leak rate — typically ≤1×10⁻³ Pa·cm³/s for micro switches per GJB 809B-2013. This means that at a pressure differential of 1 atmosphere (101.3 kPa), less than 0.001 cm³ of gas leaks through the seal per second.
To put this in perspective: at this leak rate, it would take approximately 30 years for the internal gas volume of a typical micro switch (0.5 cm³) to exchange completely with the external atmosphere. For all practical purposes, the switch is gas-tight for its entire service life.
Hermetic Seal Technologies
| Technology | Seal Material | Typical Leak Rate | Best For |
|---|---|---|---|
| Welded Metal Shell | Stainless steel (laser/TIG weld) | ≤1×10⁻³ Pa·cm³/s | Aerospace, cryogenic, radiation |
| Glass-to-Metal | Borosilicate glass fused to metal | ≤1×10⁻⁵ Pa·cm³/s | High-reliability relays, vacuum tubes |
| Ceramic-to-Metal | Alumina ceramic brazed to metal | ≤1×10⁻⁶ Pa·cm³/s | Ultra-high vacuum, space |
| Epoxy Seal | Epoxy resin | ≤1×10⁻¹ Pa·cm³/s | Industrial (NOT true hermetic) |
HK hermetically sealed micro switches use welded metal shell construction — the entire switch envelope is laser-welded after assembly, creating a monolithic stainless steel container with only the actuator passing through a sealed bellows or diaphragm.
How Hermetic Seals Are Tested
Per GJB 360B-2009, hermetic seal integrity is verified by helium mass spectrometer leak detection:
- The sealed switch is placed in a helium-pressurized chamber (typically 300-500 kPa helium)
- After pressurization, the switch is transferred to a vacuum chamber connected to a mass spectrometer tuned to helium (mass 4)
- Any helium that has penetrated the seal is detected and quantified
- The measured leak rate must be ≤1×10⁻³ Pa·cm³/s for acceptance
This is vastly more sensitive than the IP67 water immersion test and detects leaks orders of magnitude smaller than what would allow liquid water ingress.
Evaluation Criteria: Hermetic vs IP67 Decision Matrix
| Criterion | IP67 Sufficient? | Hermetic Required? |
|---|---|---|
| Altitude < 10,000m | ✅ Yes | ❌ No |
| Altitude > 15,000m | ❌ No | ✅ Yes |
| Vacuum exposure | ❌ No | ✅ Yes |
| Service life < 5 years | ✅ Yes | Optional |
| Service life > 10 years | ❌ No | ✅ Yes |
| Rapid decompression | ❌ No | ✅ Yes |
| Cryogenic (-184°C) | ❌ No (seals embrittle) | ✅ Yes (welded metal) |
| Dust/water only | ✅ Yes | Overkill |
| Outgassing-sensitive optics | ❌ No | ✅ Yes |
| Industrial cleaning chemicals | ❌ Varies | ✅ Yes |
| Food-grade washdown | ✅ Yes | Overkill |
| high-reliability industrial/mission-critical | ❌ No (MIL requires hermetic) | ✅ Yes |
Solution: HK Product Mapping by Sealing Requirement
For Applications Requiring Hermetic Sealing
KWQM4-4Z — Welded metal shell, ≤1×10⁻³ Pa·cm³/s, -184°C to +260°C
- Aerospace flight control, orbital deployment, cryogenic systems
- GJB 809B-2013 qualified, Space Grade variants available
KWQM5-2-28 — Welded shell with screw-clamp terminals
- Anti-radiation rated, cryogenic fuel systems
- Field-replaceable without soldering
For Applications Where IP67 Is Sufficient
HK-Membrane Switch — IP65 waterproof thin-film keypad
- Industrial HMI, medical devices, instrumentation
- 1M+ cycle life, fully custom design
Parameter Comparison
| Parameter | IP67 Switch | HK KWQM4 Hermetic |
|---|---|---|
| Seal mechanism | Gasket / O-ring | Laser-welded metal shell |
| Leak rate | Not specified | ≤1×10⁻³ Pa·cm³/s |
| Max altitude | <15,000m | Unlimited (vacuum-rated) |
| Temperature range | -40°C to +85°C | -184°C to +260°C |
| Seal life | 5-10 years (gasket aging) | 30+ years (metal weld) |
| Pressure cycling | Limited (fatigue) | Unlimited |
| Outgassing | Yes (elastomer seals) | None (all-metal) |
| Cost | $ (low) | $$ (moderate) |
| Test method | Water immersion | He mass spectrometer |
Conclusion
Use IP67 when: Your switch operates at ground level, needs protection from dust and water spray, has a service life under 10 years, and doesn’t face pressure differentials.
Use hermetic sealing when: Your switch operates above 15,000m, faces vacuum or rapid decompression, requires >10 year service life, or must meet high-reliability industrial/aerospace qualification standards.
For most aerospace, mission-critical, and high-reliability industrial applications, hermetic sealing is not optional — it’s a fundamental requirement defined by the qualification standard.
Related Articles
- Hermetic Micro Switches: A Guide for System Designers → — Comprehensive hermetic design overview
- How to Select Switches for Extreme Temperatures → — When IP67 fails at temperature extremes
- Long Life Cycle Switching for Railway Signal Systems → — IP-rated switches in demanding transport environments
Recommended Products
- KWQM4-4Z Hermetic Micro Switch — Laser-welded, ≤1×10⁻³ Pa·cm³/s, -184°C to +260°C
- KWQM5-2-28 Screw-Clamp Terminal Switch — Hermetic + cryogenic, screw-clamp convenience
- HK-Membrane Switch — When IP65 thin-film is the right choice
Not sure which sealing level you need? Contact our engineering team → or browse hermetic switches →