Coating Method Used for Protecting Electronic Components: Understanding Conformal Coating
In the world of electronics, the protection of circuit boards (PCBs) is paramount to their durability and performance. One essential step in this process is the application of conformal coating, a protective film that acts as an insulation layer and shields the PCB surface from various threats.
There are several methods for applying conformal coating, each with its own advantages and suitability for different production scenarios. The main methods include brushing, spraying, dipping, selective coating, and vapor deposition.
Brushing is a manual method suitable for small areas, touch-ups, or low-volume production. It allows for precise application but can be time-consuming and less consistent. Spraying, on the other hand, is a common, effective technique providing uniform coverage over the PCB, making it suitable for medium to high-volume production.
Dipping involves fully submerging the PCB in the coating material, ensuring a consistent and complete layer. This method is efficient for high-volume production but requires masking of areas that must not be coated, such as connectors or test pads. Selective coating is an automated system that applies the conformal coating only to specified areas of the PCB, reducing waste and masking needs while improving precision and repeatability.
Vapor deposition, mainly used for Parylene coatings, deposits a very thin and highly uniform layer of coating via vapor phase. It is ideal for applications requiring extremely conformal and pinhole-free protection.
Once the coating has been applied, de-masking and finishing are carried out to ensure the quality of the coating, prevent masking leakage, verify standards, and prevent coating defects.
The coating provides a barrier against particulate contaminants reaching the board surface, acts as a resistant barrier to moisture and humidity, reducing leakage current, crosstalk, and electrochemical migration across the board. It also increases the strength between dielectric conductors and protects the board from corrosion from chemical and corrosive attacks, as well as preventing damage from rough handling and thermal and mechanical stress.
The production process for conformal coating involves eight key steps, including cleaning, pre-treatment, application, curing, post-cure, inspection, and testing. Cleaning is a crucial step that removes residues from the PCB, and techniques include aqueous chemistries, solvent cleaning, and plasma cleaning.
Curing mechanisms include heat cure, moisture cure, UV cure, and catalytic cure. The coating chemistries are available based on the application of the coating, with examples including acrylic, polyurethane, epoxy, silicon, etc.
Inspection is the most important step in the conformal coating process. It includes manual inspection, UV lamp visibility, and automated optical inspection (AOI). Priming, a preparatory coating applied on a board before conformal coating, ensures better adhesion and forms a binding layer to retain the coating. The requirement for priming differs based on the type of resin.
Masking is used to keep components and designated board areas from being applied with conformal coating. Proper material selection is important to avoid masking failure.
With much research being conducted on materials, production processes, and application methods, innovations in conformal coating promise to further enhance the protection and performance of PCBs in various industries.
The integration of data and cloud computing technology can optimize the production process for conformal coating, ensuring efficient and precise application methods like spraying or automated selective coating.
The application of advanced technology in conformal coating, such as vapor deposition, not only provides a highly uniform and conformal layer but also paves the way for developing pinhole-free protection, benefiting various industries.
