How to Setup a Conformal Coating Spray Operation

Spray coating involves applying conformal coating directly onto the printed circuit board (PCB) by spraying. This method is usually done manually in a spray booth or via aerosol, but it can also be automated or robotic for specific coating tasks.

PCBs are safeguarded by spraying liquid conformal coatings like acrylic, epoxy, silicone, and urethane onto their substrate surfaces. This protective layer ensures the continuous functionality of the PCBs. A crucial aspect of any spray coating application involves determining:

• The project’s volume
• Production time needed to complete each step of the process
• The number of workers required to complete the project
• Type of equipment is needed

Versatile spray applications offer cost-effective solutions. They can be manually applied on a benchtop for small-scale rework and repair tasks efficiently. For medium-level production, spray operations can be upscaled in a dedicated spray booth. With a clean PCB and a coating material free from adhesion issues, a skilled operator can achieve a superior surface finish compared to other liquid application methods. Automated aerosol spray processes ensure precise coating and quicker production, with robotics playing a vital role in high-volume spray applications.

Spray Coating Processes

Manual Spray Coating Processes

When done manually or with aerosols, film material is typically diluted with solvents to achieve a predetermined viscosity and sprayed from all four quadrants at a 45° angle. Manual processes are best used for reworking a PCBs to meet project specifications. They are less reliable for initial coating due to human error leading to inaccuracies in coating thickness and necessitating rework.

Versatile non-aerosol processes can be manually applied with a spray gun. Automated non-aerosol spray equipment drives the coating through a needle to the substrate surface. Unlike aerosol methods, coating material is not atomized by compression; rather a fan in the nozzle sprays the coating onto the substrate. Non-aerosol sprays can apply a denser coating on a surface, ideal for tasks requiring a thicker application.

Special equipment is required for applying conformal coatings by aerosol methods, to appropriately atomize film material into a fine mist. Using air pressure to force liquid coating through a small-vented cavity, spray misting promotes an exceptionally even, but very fine, film across the substrate surface. The initial coating layer will be very thin, necessitating additional spray applications — multiple passes build the coating up to acceptable thickness. However, good masking is necessary to contain the process because aerosol spraying tends to distribute coating material everywhere.

Robotic/Automated Spray Coating Processes

Robotic coating offers significant advantages for large-scale batch assignments by providing cost-effectiveness and consistency. The precision of selective robotics enhances production efficiency by reducing time and ensuring precise coating thickness control. However, even with programmable functions like plating and un-plating, masking remains crucial to protect specific areas like connectors and mounting holes that are challenging to program around.

Despite its benefits, misalignment of PCB components during automated spray applications can cause damage and functional issues. Repairing essential mechanisms like spray heads is both time-consuming and costly, highlighting the importance of strategic management in robotic decisions. While robotics can streamline processes by minimizing masking procedures, careful implementation is key to prevent downtime and maintain production efficiency.

Conformal Coating Spray Facility Requirements

A spray coating facility for high-quality conformally coating requires a well-ventilated workspace. Additional recommended features include:

• Spray booth: Allows easy, even coating application with a high-quality spray gun, efficiently extracting fumes in the process. Repeat application generates optimal coating finish and protection. Positioning UV light over the PCB during coating improves operator vision and control, minimizing the development of shadowing effects; a manual or automatic turntable further limits shadowing.
• Curing cabinet: For storage of drying PCBs after application, the curing cabinet extracts air surrounding them, drying assemblies while removing potentially hazardous fumes. Each PCB’s stationary position within the cabinet ensures the coating does not flow, which would cause deviation in the film’s thickness, challenging its capacity to provide specified conformal protection. Airborne particles are also prevented from adhering to the wet coating.
• UV inspection booth: Long-wave UV lighting is recommended to inspect the still-fluorescing film. Studying the PCB with the intensified UV lighting in a dark, enclosed space detects regions where manual touchup is needed, allowing final inspections to commence. Electrostatic discharge (ESD) points are attached at this stage to prevent development of any ESD issues.

Providing and maintaining these production mechanisms significantly improve operator performance, encouraging optimal results. Enhancing and upholding these production mechanisms greatly boosts operator performance, fostering optimal outcomes. With over 50 years of experience, Specialty Coating Systems combines expertise with a team of highly skilled professionals to meet customer’s spray coating needs for liquid conformal coatings. Contact us today for more information about our spray coating services or to request a quote.