Conformal coating: acrylic, silicone or PU?
Conformal coating protects circuit boards from moisture, dust, salt spray and chemicals. The three most common types are acrylic, silicone and polyurethane, each with its own strengths in environmental durability, reworkability and cost.
Choosing the right coating system at the design stage helps avoid process change costs later on. This article compares these three types according to the practical criteria that manufacturing engineers care about.
Acrylic: easy to apply, easy to rework
Acrylic coatings dry quickly by solvent evaporation, producing a hard, clear film. Their biggest advantage is that they can be redissolved with solvent for component rework. Acrylic offers good moisture resistance at a reasonable price, making it suitable for consumer electronics and indoor control boards. Its limitation is poor resistance to solvents and fuels.
Silicone: heat resistant and flexible
Silicone coatings perform reliably from -55°C to 200°C, and their good elasticity reduces stress on solder joints under large temperature swings. They are a popular choice for automotive electronics, high-power LED lighting and outdoor equipment. Silicone is harder to rework than acrylic, and the risk of volatile siloxane affecting relay contacts must be considered.
Polyurethane: superior chemical resistance
PU coatings offer good resistance to solvents, oils and abrasion, making them suitable for boards in industrial or marine environments. In exchange, PU takes longer to cure and almost always has to be removed mechanically for rework.
Quick comparison table
| Criteria | Acrylic | Silicone | Polyurethane |
|---|---|---|---|
| Operating temperature range | -55 to 125°C | -55 to 200°C | -40 to 130°C |
| Moisture resistance | Good | Very good | Very good |
| Solvent resistance | Poor | Moderate | Good |
| Reworkability | Easy | Moderate | Difficult |
| Relative cost | Low | High | Moderate |
Selection guide by application
- Home appliance control boards: solvent-based or water-based acrylic.
- Automotive electronics, LED lighting, outdoor inverters: silicone.
- Industrial equipment exposed to oil and chemicals: polyurethane.
- Lines that need fast curing: UV coatings with secondary moisture cure.
Most coatings today contain a fluorescent tracer for coverage inspection under UV light, making quality control more convenient.
AMS supplies coatings from Dow, Henkel and Dymax along with sample coating trials. Contact AMS Vietnam for advice on the right coating system for your product.
