INFICON IP67 and Helium Leak Testing: How Tight is Tight Enough?
Application Note
Dichtheitsprüfung nach Schutzklasse IP67
Many enclosures for electrical components, such as sensor housings or battery housings for Lithium-ion batteries, are designed according to IP67 protection class. The second digit – “7” – indicates protection against water ingress. The test requires the component to be immersed in 1 meter deep water for 30 minutes without water penetrating and potentially damaging the electronics.
Many customers face the question of which helium leak rate specification corresponds to this requirement. INFICON conducted an experiment to answer this question.
Experimental Setup
A test part was created that could be equipped with artificial leaks of various sizes. The artificial leaks consist of glass capillaries with a defined diameter to represent a specific leak size. Capillaries from 10 μm to 100 μm were tested. The test part was filled with water and pressurized to an overpressure of 100 mbar (~1.1 bar absolute pressure), which corresponds to the pressure at a depth of 1 meter. Subsequently, the outflow of artificial leakage was observed for 30 minutes, and the amount of escaping water was recorded.
Pressure: 0.1 bar relative
Results of the Water Test
The results of the water test are summarized in the table below.
| LEAK PATH DIAMETER | LEAK RATE | AMOUNT OF WATER DRIPPING OFF IN 30 MIN | AVERAGE TIME PER DROP |
|---|---|---|---|
| Ø0.020 μm x 10.5 mm | 0.0008 sccm (1 x 10⁻⁶ mbar l/s) | No droplet can visually be seen | n.a. |
| Ø0.010 μm x 10.5 mm | 0.012 sccm (2 x 10⁻⁴ mbar l/s) | One drop forms but does not drip off within 30 min | Drop may drip off after 40 - 50 min depending on temperature and humidity |
| Ø0.025 μm x 10.5 mm | 0.03 sccm (5 x 10⁻⁴ mbar l/s) | 3 drops | 8:30 - 9:00 min |
| Ø0.029 μm x 10.5 mm | 0.05 sccm (9 x 10⁻⁴ mbar l/s) | 3-4 drops | 7:30 - 8:30 min |
| Ø0.040 μm x 10.5 mm | 0.2 sccm (3.1 x 10⁻³ mbar l/s) | 20 drops | 1:30 min |
| Ø0.100 µm x 10.5 mm | 7.6 sccm (1 x 10⁻¹ mbar l/s) | 524 drops | 3 seconds |
The test revealed that the equilibrium between water pressure and adhesion forces occurs with a leak channel of just under 20 μm in diameter.
Conversion to Leak Rate Specification
The following diagrams show the relationship between the amount of water that flows through a possible leak in 30 minutes and the corresponding gas leak rate. Helium and air leak rates differ only by about 7% – corresponding to the ratio of their dynamic viscosities – and can therefore be considered almost identical. The yellow lines show the measurement results for a glass leak channel; the remaining lines were transferred to other materials based on material properties.
Leak Channels from Different Materials
Pressure: 1.1 bar → 1 bar (15.95 → 14.5 psi) (e.g., sniffing)
Helium Leak Rate: 1.1 → 1 bar [mbar l/s]
Number of Water Drops in 30 Minutes
Materials: Alu, Glass, PVC, Steel/PC/PE/ABS
Many components with IP67 specifications can only withstand low pressure differences (typically 100-200 mbar) without damage to themselves or their seals. The diagram above shows leak rates at 100 mbar pressure difference. Depending on how much water your component can tolerate, the maximum permissible gas leak rate can be determined. For example, if your housing is made of ABS or steel with a polymer seal, you should check for a leak rate below 3 x 10⁻² mbar l/s (~1.8 sccm) if you tolerate a few drops (orange/green line). If no water ingress is to be allowed, a leak rate of 5 x 10⁻³ mbar l/s (~0.3 sccm) is recommended. If your component is made of aluminum with a polymer seal – meaning the leak path involves aluminum on one side and polymer on the other – choose a middle ground between the two materials: check for approximately 9 x 10⁻⁴ mbar l/s (~0.05 sccm) if a few drops are permissible, or 2 x 10⁻⁴ mbar l/s (~0.01 sccm) if absolutely no water ingress is to be allowed.
Conclusion
Leak testing according to IP67 requires sensitive leak detection methods that can detect leak rates well below 1 sccm. Gas leak testing is the method of choice for these applications. Different pressure conditions and different materials lead to different leak rate specifications. Please contact INFICON with your specific testing requirements, and they will be happy to help you achieve the highest efficiency and reliability in your testing!
