Enhancing Quality through Improved Conformal Coating Application Process
Conformal coating plays a crucial role in the PCBA process. Prolonged exposure of circuit conductors or electronic components to the air can lead to contamination or damage, thereby affecting their lifespan. By implementing the conformal coating process in electronic projects, this issue can be effectively addressed. The protective film material comprises a polymer thin film chemical coating, which is applied to the irregular areas of the PCBA board. This coating enhances dielectric resistance and reliability. Let us engage with a professional PCBA company like FS Technology to explore and enhance the project quality through this process step.
How to apply conformal coating
Step 1: Material Selection
During the PCBA manufacturing process, selecting an appropriate material for the board surface is crucial. As your chosen PCBA supplier, FS Technology offers a range of customized options, including Acrylic, Polyurethane, Epoxy, Parylene, Silicone, and Paraxylylene. The selection of different materials for the conformal coating process is guided by your cost considerations and specific project requirements. For instance, Polyurethane may be suitable for industrial control board with higher profit margins, as it provides excellent resistance to temperature and chemical corrosion, despite its relatively higher price.
Step 2: Prepare PCBA Board
This process entails meticulous cleaning of the PCBA board, ensuring its pristine condition. The conformal coating process involves the application of molten chemicals onto the board’s surface, resulting in the formation of a protective film. It is crucial to note that any dust or contaminants present on the board itself will also be encapsulated within the coating during this procedure.
Step 3: Conformal Coating Applications
Conformal coating application on the board is a widely employed technique in the industry. While the process may appear straightforward, it requires the expertise of skilled individuals to ensure precise application and high-quality coating results. The process necessitates the use of specialized tools, including a brush, a dedicated coating container, and a suitable workspace for the application. To begin, immerse the brush into the coating container and meticulously apply it onto the board’s surface.
This technique involves the application of coatings using aerosols, batch spraying, or selective spraying.
- Aerosol: The application utilizes a spray gun configured with a solvent-based coating. This method is cost-effective, enabling high-speed application while maintaining a quality finish. It is a preferred alternative to brushing due to its efficiency.
- Batch Spraying: Employs a compressed air gun to achieve a precise finish. This technique requires a spray gun, spray booth, and air compressor. Proper adjustment of pressure levels and selection of suitable materials are essential considerations. Additionally, the coating viscosity must be appropriately configured.
- Selective Spray: It is employed to apply coatings to specific areas, avoiding areas with connector connections. This technique allows for targeted application while minimizing the risk of interfering with connectors.e
This method, known as dip coating, is a traditional technique where boards are immersed in a container containing coating material. Several factors are closely monitored during this process, including immersion speed, coating dwell time, and the withdrawal speed of the board. Solvent-based conformal coatings, such as acrylics and urethanes, are commonly utilized in this method.
In this technique, the coating is applied to the board in a gaseous form. It is a more expensive process primarily employed in medium to high-volume production. The process consists of four steps, which are outlined below:
- Parylene Vaporization: The parylene material is vaporized to form a gaseous state. This typically involves the controlled heating of the solid parylene material.
- Pyrolysis: The vaporized parylene material undergoes pyrolysis, a chemical decomposition process that breaks it down into reactive monomers or dimers.
- Coating Deposition: The pyrolyzed parylene molecules are deposited onto the board, forming a conformal coating. This deposition can be achieved through a variety of methods such as chemical vapor deposition (CVD) or physical vapor deposition (PVD).
- Cold Trap: During the coating deposition process, a cold trap is utilized to collect any excess or unreacted parylene material. This helps ensure the quality and purity of the deposited coating on the board.
Problems in PCB Conformal Coating Process
The occurrence of dewetting happens when the coating fails to spread or wet certain areas of the substrate and subsequently recedes, leaving adjacent regions exposed. This phenomenon is typically observed when common residues like flux, grease, oil, or cutting fluids remain on the surface, hindering the natural flow of the coating and impeding its ability to spread and level properly.
To address the issue of dewetting, thorough cleaning of the substrate is essential to ensure the complete removal of any residual contaminants. It is important to employ appropriate cleaning methods and cleaning agents compatible with the substrate material to achieve a surface free from contaminants. This can include processes such as ultrasonic cleaning, solvent cleaning, or chemical cleaning, depending on the nature of the residues and the substrate’s sensitivity.
Additionally, preventive measures can be implemented to minimize the occurrence of dewetting. These measures may include controlling environmental factors such as temperature and humidity, and ensuring proper handling and storage of substrates and coatings to avoid contamination.
As the name implies, results in an uneven surface with a texture resembling fish scales. This issue arises from the spray application technique, specifically when the spray pressure is set too low, leading to inadequate atomization, or when an incorrect diluent is used.
To address this issue, it is crucial to carefully review and follow the manufacturer’s recommendations outlined in the product Technical Data Sheet (TDS). The TDS provides valuable information regarding the optimal spray equipment setup, including the appropriate pressure, nozzle size, and spray pattern for the specific coating material being applied. By using the recommended spray settings, the coating material can be properly atomized, ensuring uniform distribution and coverage on the substrate.
In addition to the spray settings, selecting the correct diluent or solvent is crucial to maintain the desired viscosity and flow properties of the coating material. The TDS provides guidance on the compatible diluents that can be used to achieve the desired viscosity for the specific coating product. Using the incorrect diluent can adversely affect the coating’s flow and leveling characteristics, resulting in the fish scale-like surface.
Care should also be taken to ensure proper mixing and agitation of the coating material before application. Thoroughly stirring the coating material using recommended techniques, such as mechanical mixing or gentle agitation, helps to ensure uniform distribution of any additives or pigments within the coating formulation.
The occurrence of a foaming surface is attributed to three factors:
- Excessive coating pressure that introduces air into the liquid coating.
- Rapid drying of the coating, preventing sufficient flow and degassing of the film.
- Application of excessively thick coating, resulting in solvent vapor entrapment.
To prevent the occurrence of a foaming surface, it is important to avoid applying thick coatings. Instead, it is recommended to build up the desired film thickness through the application of multiple thin layers. This allows each layer to dry and level properly before applying the next, minimizing the risk of foaming.
Controlling the drying process is also important in preventing foaming. It is essential to allow sufficient drying time for each layer before applying the next one. This allows the coating to level out, release trapped air, and promote a smooth surface. Factors such as temperature, humidity, and airflow should be carefully controlled to facilitate proper drying without promoting excessive solvent evaporation.