UV adhesives fixing voice coils
UV adhesives that cure in just a few seconds help speaker plants significantly speed up the bonding of voice coils, magnets and other parts in the magnetic circuit, while also reducing the floor space needed for curing ovens.
In the past, many lines used two-component epoxy or heat-cure adhesives, which required waits ranging from tens of minutes to several hours. Work-in-progress piled up on racks, was prone to knocks and was hard to trace. Switching to UV adhesives is an improvement many plants have chosen.
Especially for microspeakers in phones and earbuds, the small part size makes loading trays into ovens both slow and prone to misalignment. Curing in place right on the fixture solves both problems.
Why UV adhesives suit speakers
Acrylic or cationic epoxy UV adhesives cure when exposed to light at wavelengths of 365–405 nm. The time from dispensing to the part being secure enough to move to the next station drops to just 3–10 seconds. As one-component adhesives that require no mixing, they generate little waste and deliver consistent quality.
Reference specifications
| Parameter | UV voice coil bonding adhesive | Traditional 2K epoxy adhesive |
|---|---|---|
| Fixture time | 3–10 seconds | 20–60 minutes |
| Operating temperature | -40 to 150°C | -40 to 180°C |
| Viscosity | 5,000–30,000 cP | Changes with time after mixing |
| Required equipment | UV LED lamp, dispenser | Mixer, curing oven |
Handling shadow areas
The weakness of UV adhesives is areas the light cannot reach, such as the gap between the magnet and the pole plate. There are three common approaches:
- Choose a dual-cure UV and heat adhesive, with a light bake at 80–120°C to complete curing in shadow areas.
- Choose a UV adhesive with secondary moisture cure.
- Adjust the design so the lamp can illuminate the bead from both sides.
Quality control on the line
UV adhesives can contain fluorescent tracers so automated inspection cameras can detect missing adhesive. Lamp intensity should be measured periodically with a radiometer because LED heads degrade over time. Nickel- or epoxy-coated magnet surfaces need to be degreased before dispensing to ensure adhesion.
For occupational safety, UV curing stations should have shielding and workers should wear UV-filtering glasses. Uncured adhesive can irritate skin, so nitrile gloves are required and adhesive residue on tools should be wiped off with alcohol. During the changeover, it is advisable to run both methods in parallel on part of the line to compare rub-and-buzz defect rates and voice coil push-out strength.
AMS supplies UV adhesive lines from Dymax and Henkel Loctite and helps customers choose suitable UV LED lamps. Contact AMS Vietnam to test samples on your own speaker parts.
