Product Development - Summary of Key Points for Waterproof Structure

 Waterproofing is one of the more challenging aspects in structural design, demanding high standards in design approach, manufacturing processes, and precision control. Below are common waterproofing design methods:

❇️ Common Waterproof Structural Methods:
Rubber gaskets, two-shot (overmolded) injection molding, ultrasonic welding, potting (encapsulation), adhesive sealing (caulking), double-sided tape, waterproof breathable membranes, and nano-coatings.

➡️ Key Design Considerations for Waterproofing:

1️⃣ Waterproofing Between Upper and Lower Housings:
If future disassembly and maintenance are required, a compression-type silicone gasket is typically used. The silicone hardness usually ranges from Shore A 40° to 50°. Ideally, one housing features a protruding rib while the other has a matching groove. Compressing the silicone gasket between them can achieve IP68 waterproof rating. Note: the groove width should be slightly larger than the outer diameter of the rubber gasket.

2️⃣ Embedded Small Housing Waterproofing:
For small or flat housings inserted into a main enclosure, a side-compression silicone gasket is commonly used. The interference fit is typically 0.1–0.2 mm, with a silicone hardness around Shore A 45°.

3️⃣ Lens Waterproofing:
Lenses are generally secured using double-sided adhesive tape or liquid adhesive (glue dispensing). Double-sided tape should be at least 1.5 mm wide to ensure effective waterproofing and must be held under pressure for a specified duration. If the bond width is less than 1.5 mm, liquid adhesive is preferred—but note that this method typically loses its waterproof capability after disassembly.

4️⃣ Button Waterproofing:
In compact devices like smart wristbands, dual rubber rings are often employed due to space constraints. The mating surfaces require good surface finish, with an interference fit of approximately 0.1–0.12 mm. For handheld products with larger buttons, two-shot molding is common—using rigid plastic for the main housing and soft elastomer for the button.

5️⃣ Waterproof Breathable Membranes:
Used primarily for acoustic components like speakers, these membranes usually come with a pressure-sensitive adhesive backing and typically meet IPX4 requirements. For higher waterproof ratings, a “sandwich” structure can be adopted—for example, sealing the membrane between two parts using ultrasonic welding on both sides.

6️⃣ Charging Port Plug Waterproofing:
Side-compression soft rubber plugs are commonly used. A purely soft rubber plug typically achieves IPX4. Higher waterproof ratings can be attained by combining a rigid plug body with a rubber gasket or using two-shot molding.

7️⃣ Threaded Joint Waterproofing:
Two approaches exist: (a) compressing a sealing ring against the top cover face, or (b) placing a rubber O-ring at the thread’s end and achieving sealing via radial compression.

🌟 Important Note: Waterproof design is a systemic engineering challenge. Failures often occur during thermal cycling or long-term aging tests. If the product operates or is stored in humid environments, external structural waterproofing alone is insufficient. Internal PCBs should be coated with conformal coating or nano-coating, and connectors may even require potting to ensure long-term reliability.