Waterproofing sports earbuds with nano coating

Hydrophobic nano coatings protect the circuit boards, microphones and speaker diaphragms of sports earbuds from sweat and rain, helping products achieve IPX5 water resistance or higher without the need for complex gaskets.

Sweat contains salts and mild acids that corrode circuits faster than clean water. As a result, sports earbuds often fail at the charging port, microphone or speaker circuit after a few months of training. Nano coating is a solution that is lightweight and does not affect product dimensions.

Sports earbud users often run in the rain, cycle long distances or do high-intensity gym workouts, so their exposure to liquids is much greater than with regular earbuds. Warranty replacements due to water damage are a significant cost for brands.

How nano coatings work

The coating is only a few tens to a few hundred nanometers thick, typically a fluorinated polymer. When applied to a surface, it lowers the surface energy, causing water droplets to bead up and roll off instead of spreading. The water contact angle typically exceeds 110 degrees.

Because it is so thin, the coating does not obstruct sound transmission through microphone meshes and speaker diaphragms, and in many cases connectors do not need to be masked as they would with traditional conformal coatings.

Two common coating methods

Dip or spray coating with solution

Low capital investment, suitable for medium volumes. The circuit board is dipped into a nano solution in a fluorinated solvent and left to dry at room temperature for a few minutes.

Plasma coating in a vacuum chamber

Coats evenly even in small gaps, suitable for high volumes and demanding requirements. Equipment investment is higher, but the cost per unit is low.

Tests to verify water resistance ratings

• IPX4 and IPX5 water spray tests per IEC 60529.
• Cyclic artificial sweat spray tests with leakage current measurement.
• Checking microphone sensitivity and speaker response before and after coating.
• Light abrasion tests to assess coating durability during assembly.

One caveat is that nano coating does not completely replace a sealed design. For IPX7 immersion ratings, it should be combined with gaskets or sealants at housing joints.

Placing the coating step in the production line

Typically, nano coating is performed after soldering and functional testing of the circuit board, before it is assembled into the housing. Points that require electrical contact, such as pogo charging pins, can be masked with temporary tape or wiped clean after coating, depending on the type of solution. For quick inline inspection, some solutions contain fluorescent tracers, allowing a UV lamp to be used to confirm coverage. The water contact angle should be measured periodically on test coupons to monitor the solution concentration in the bath.

AMS supplies nano coating solutions and supports sample trials for earbud and smartwatch manufacturers. Contact AMS Vietnam to schedule a coating trial.