In the production and manufacturing of circuit boards, some products require the application of conformal coating based on specific needs. Conformal coating is a type of specialized polymer film that protects circuit boards, components, and other electronic devices from adverse environmental conditions. These coatings are not limited by PCB structure or other environmental factors; they provide higher dielectric resistance, thereby protecting the circuit board from corrosive environments, moisture, and contaminants such as dirt and dust.

Materials and Applications of Conformal Coating

Depending on the needs of the circuit board, conformal coatings can be made from acrylic resin, silicone resin, polyurethane resin, or other application-specific compounds (such as epoxy resin). These coatings can be applied by brushing, spraying, or immersing the circuit board in the coating material.

1. Acrylic Resin:

         a. Characteristics: Provides good flexibility and meets general protection needs.

         b. Advantages: Noted for its high dielectric strength, good moisture resistance, and abrasion resistance.

         c. Applications: Suitable for electronic devices that require basic protection.

2. Silicone:

         a. Characteristics: Offers excellent protection across a wide temperature range, with good chemical resistance, moisture resistance, and salt spray resistance.

         b. Advantages: Highly flexible, able to withstand vibration stress, but not very abrasion-resistant.

         c. Applications: Typically used in high humidity environments and can be applied to LED lights without altering color or strength.

3. Polyurethane:

         a. Characteristics: Known for its excellent moisture resistance and chemical resistance, and is highly abrasion-resistant.

         b. Advantages: Strong solvent resistance, forming a conformal coating that is difficult to remove.

         c. Applications: Widely used in high-demand fields such as aerospace.

4. Epoxy Resin:

         a. Characteristics: Designed for specific applications, providing strong protection.

         b. Applications: Suitable for scenarios requiring exceptionally strong protection.

Differences Between Conformal Coating and PCB Surface Finishing

Conformal coating and PCB surface finishing are different processes, with the main differences as follows:

1. Conformal Coating

        a. Application Timing: Applied after the circuit board assembly, i.e., after SMT (Surface Mount Technology) production.

        b. Purpose: Protects the circuit board during operation from environmental factors.

2. PCB Surface Finishing

        a. Application Timing: Part of the PCB manufacturing process, applied before the circuit board assembly.

        b. Purpose: Protects the copper surfaces from corrosion before assembly and prepares the board for subsequent soldering.

        c. Common Processes: Includes Hot Air Solder Leveling (HASL), as well as immersion treatments with tin, silver, and gold.

Three Methods for Applying Conformal Coatings

Currently, there are three main methods for applying conformal coatings:

1. Manual Spraying: This method involves using aerosol cans or hand-held spray guns to apply the conformal coating. It is generally used when fixed equipment is not available and is typically employed for small-scale production. For example, in prototype production lines used during the design and development phase, this method is often used. However, it can be time-consuming as care must be taken to avoid applying the coating to undesired areas. Consequently, the final result largely depends on the operator, leading to potential variability in coating quality between boards.

2. Automated Spraying: This method uses a programmable spraying system where the circuit boards are moved on a conveyor belt. As the boards pass specific positions, a spray head applies the coating. This approach ensures more uniform application compared to manual spraying.

3. Selective Coating: This is an automated conformal coating process that applies the coating only to specific areas of the circuit board. It is suitable for high-volume production and is somewhat similar to selective wave soldering.