How to Design Moisture Resistant Hearing Aids

With miniature circuitry and tiny micro-chips, designing reliable, modern hearing aids is a complex task. While they are critical medical devices, like most electronics, they are sensitive to moisture. Water, sweat, skin oils, and cleaning fluids can cause corrosion and distortion in sound quality if there is ingress in the hearing aid casing, with the potential of cascading into catastrophic circuit problems. Additionally, ear wax, temperature changes, and salt can have detrimental effects on sensitive hearing aid components, influencing performance or causing failure. Finally, water penetration, body chemistry, and build-up of cerumen can all lead to battery contact corrosion. Left unaddressed, all of these factors increase repair costs and compromise warranties.

Because hearing aids are an investment for most users and patients frustrated by premature failure, the industry is focused on creating more reliable devices. It continues to invest in producing hearing aids that can remain dependable regardless of exposure to the hazardous environment of the human ear. In a recent article on Medical Device and Diagnostic Industry Online, our EVP of technology, Zsolt Pulai, wrote about the challenges of designing reliable hearing aids. Although hearing aids have made great strides in technology (many are now devices with bandwidths that reach 8000 Hz, and some with a high-frequency response extending beyond 10,000 Hz, significantly improving hearing quality), they are still susceptible to contaminants. Pulai pointed out a cross-sectional study on technical failures of hearing aids, citing the main technical failures primarily caused by moisture and oxidation of components.

Waterproof Hearing Aids vs. Water-Resistant Hearing Aids

Because hearing aids are an investment for most users and patients frustrated by premature failure, the industry is focused on creating more reliable devices.

All hearing aids receive “Ingress Protection (IP) Ratings” “bott to help consumers determine how resistant they are to dust and water. These standards, a contribution from the International Electrochemical Commission, use two digits to rate the degree of protection against debris and moisture. The first digit measures debris protection, the second, moisture. In general, the higher numbers in the code, the better protection the hearing aid design provides.

For example, a liquid ingress rating of 7 (IPX7) means the device is “water protected,” it can be submerged in up to 1 meter of water for up to 30 minutes and still maintain standard functionality.

For reference, here is a table describing liquid ingress standards and how HZO’s hearing aids protective coatings measure up.

Ingress Protection Level Description of Protection Provided HZO Coating Performance
0 None Exceeds
1 Dripping Water Exceeds
2 Dripping Water When Tilted at 15° Exceeds
3 Spraying Water Exceeds
4 Splashing of Water Exceeds
5 Water Jets Exceeds
6 Powerful Water Jets Exceeds
7 Immersion, up to 1 Meter Depth Exceeds
8 Immersion, 1 Meter or More Depth Exceeds

Download our Ingress Protection Checklist

As you can see, our hearing aid coatings exceed all IP ratings, and in fact, Parylene coatings can produce completely waterproof hearing aids. In other words, the medical devices could be submerged throughout the product’s life and continue to function, which would be a notable differentiator and consumer draw.

Parylene and Nanocoatings for Hearing Aids

Nanocoatings protect internal components in a hearing aid by repelling liquid – allowing moisture to bead off. Nanocoatings protecti internal components in a hearing aid by repelling liquid – allowing moisture to bead off. Hydrophobicity can extend hearing aid life significantly, improve reliability and performance, and reduce maintenance. Our nanocoating method is plasma-enhanced chemical vapor deposition; the benefits are discussed below.

Plasma-Enhanced Nanocoating Benefits:

  • Increases film quality at low temperatures
  • Multilayer films of varying chemical characteristics can be delivered
  • Scalable processes for high volume manufacturing
  • Competitive pricing
  • Material selection can be optimized to various standards
  • Repeatable, scalable solution

Download the HZO Nanocoatings Datasheet

Parylene Thin-film Coatings for Waterproof, Sweat-Resistant Hearing Aids

Consisting of a protective polymer layer 12-25 microns thick, Parylene coatings are non-conductive dielectric materials that protect components from corrosion and shield them from fungus, moisture, dust, spray, and even earwax. Parylene can also prevent damage from thermal and mechanical stress, rough handling, or falls.

HZO’s Parylene Benefits

  • Proprietary, optimized equipment allows the Parylene process to ramp up to mass production
  • Automated masking and demasking drives down Parylene pricing
  • A turnkey solution provides materials, equipment, people, and processes as an end-to-end coating solution


HZO Hearing Aid Case Study

HZO worked closely with AXIL, a manufacturer of hearing aids that augment user’s (including outdoor enthusiasts, hunters, and industrial workers) hearing while simultaneously protecting that same hearing from harmful loud sounds, to protect the internal circuitry of the small and rugged devices. Now considered “the most versatile earbuds on the planet,” AXIL received accolades for achieving its protection requirements thanks to HZO.

If you are interested in HZO’s Parylene or nanocoating solutions, reach out today with a question or fill out a quote form for more information.

Mallory McGuinness

As a veteran writer with over a decade of writing experience, Mallory McGuinness has spent the last two years at HZO learning about coating technology from the best minds in the industry. Professionally, Mallory is especially interested in the process of problem-solving and watching how the engineering team develops solutions that ensure business requirements are met. In her free time, you can find Mallory walking her dog Ebbie, fueling up on coffee, watching the Simpsons, and referencing the Simpsons.

All of Mallory’s blogs are reviewed for accuracy before publication.

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