Selective Conformal Coating in Electronics Manufacturing

Look around. It’s no secret that electronics have become an integral part of the human experience. From smartphones and automobiles to medical devices and exercise equipment, each device serves a vastly different purpose in our lives. Still, they share one similarity—they are all equipped with some electronic circuitry. These circuits are usually designed on a rigid or flexible printed circuit board (PCB)and integrated into various electronic devices. However, because of how electronic devices are used, they are especially susceptible to failure if exposed to contaminants such as dust particles, moisture, humidity, corrosive substances, and other foreign materials. Manufacturers and consumers both want the same thing: they want their products to last. In order to extend a product’s lifecycle, it is essential that its PCB must be well protected from exposure. Enter the conformal coating.

Conformal coating is one of the most commonly used methods for protecting electronic devices. The practice involves applying a liquid coating over a PCB, which then solidifies to become a thin protective barrier. Modern conformal coating equipment is designed to apply coatings onto the surface of an electronic assembly in a selective manner. Due to the electrically insulating properties of conformal coatings, the equipment is programmed to only coat desired areas of a PCB by accurately controlling the placement of the liquid to ensure proper coverage of components and solder joints while avoiding any connectors or contact points. Alternate applications can be run using a dip or bulk spray process where the entire PCB assembly is coated, but this requires the use of masking in order to keep coating off contact points. Masking involves using tapes, liquids, or specially designed fixtures to shield the PCB from the liquid as it is being applied. This process requires an operator to apply and or remove the masking materials.

An automated selective coating system is the ideal choice for medium-to-high volume production of PCBs where accuracy, repeatability, and minimal operator handling is required. The system’s selective application ability will greatly reduce or eliminate the need to use masking materials to achieve the desired results. Eliminating the necessity for masking reduces the cost of labor and materials used in the manufacturing process. Additionally, since the coating is only applied where needed on the PCB, there is very little waste of the coating chemical lost to overspray beyond the PCB or target areas. These efficiencies in material and labor usage all amount to an increased return on investment (ROI).

Once the liquid has been applied to the PCB, the coating is cured to create a solid, protective layer. Curing can be accomplished by various methods such as heating, exposure to moisture, high-intensity ultraviolet light, solvent evaporation, or chemical reaction. There are numerous types of coatings available, including acrylic, silicone, epoxy, and urethane. Each coating material has its strengths and weaknesses and should be evaluated prior to designing into a product specification.

Selective conformal coating equipment has evolved from simple XYZ robots using a single spray valve into multi-axis, multi-head systems with many integrated features. The use of vision systems, flow monitoring, spray pattern measurement, viscosity control, and fluid metering are often integrated into automated systems to ensure coating results remain stable and consistent. Electronics manufacturers have the choice of running the process either offline in a standalone configuration or integrated with their existing electronics production line. Coating machines can also be connected to factory information systems to track useful production metrics such as machine uptime, errors, coating usage, or any other data point relevant to the process used at the factory site.

Providers also offer tools used beyond the conformal coating process. Alongside the conformal coating system, equipment such as curing ovens, cleaning, and inspection systems can be delivered as a comprehensive package with all the means required to provide a repeatable and stable manufacturing process.

When evaluating a conformal coating process for electronic assembly, several factors should be considered early in the design to avoid future issues. For example, a PCB that is used in an automotive environment will need to withstand broader temperature changes than a PCB used in a child’s toy. There is an abundance of material choices and processing methods, and there is no one-size-fits-all solution that is suitable for all end-use environments. Designers and Production Managers should perform due diligence to fully understand the equipment, application, and material guidelines prior to implementing a conformal coating process.

No matter the product or device, if there are electronics involved, it is paramount to ensure they are protected from the environment. Conformal coating is currently the most widely adopted solution. A properly deployed selective conformal coating process has been proven to lower manufacturing costs and reduce variation between coated assemblies while offering high-level traceability and flexibility, ultimately saving the manufacturer time and money.