For conformal coating, there are many different facets, from equipment and applications to various coating forms. Conformal coating is a non-conductive dielectric protective layer that is added to the assembly of the printed circuit board to protect the electronic assembly from toxicity, salt spray, moisture, fungus, dust, and corrosion caused by harsh or extreme environments. Conformal coatings are generally used in products that are manufactured for use in outdoor environments where heat and moisture are common. The coating also avoids damage caused by rough handling, installation, and mechanical and thermal stress reduction.
Why conformal coating?
The conformal coating extends the product's life during its operation. At the same time, it helps to improve the dielectric strength between conductors in order to make the PCB's design more compact and small. It also acts against abrasion and solvents to protect circuitry and components.
The coating is clearly visible as a transparent and shiny substance after the coating process is complete. Many coatings are rough while others have a somewhat rubbery texture. Some coatings include a marker that, when viewed under UV light, appears greenish-white. This marker allows for easy inspection during the development of the thoroughness of the coating.
In the past, coatings have only been applied as the cost to military and life/medical products, and the process per device has been significantly higher. The advancement of materials and new processes in recent years has made it possible to cover a wider range of items, including a wide range of consumer electronics products. When prices continue to fall, conformal coating for circuitry and electronic components becomes increasingly common, specifically as these products continue to shrink in dimension and size.
Conformal coating applications
Conformal coatings are very thin material layers designed to protect a circuit board's surface. Such layers are added to the circuit board or substrate and serve as a defense against harsh elements. When the finished product comprising the printed circuit board is exposed to a harsh environment, the conformal coating can be used. Such environments may include heat, chemicals, moisture, or any substance that could harm a circuit or substrates mechanics.
It is vital to understand how rework and repair issues are affected when choosing a conformal coating material. The need to rework or fix a conformal coating can occur due to a variety of process/product specifications or part replacement issues at any time after completion of an assembly. Therefore, when choosing coating chemistry, a rework of conformal coatings needs to be addressed at the front.
The application method of coating materials is a key consideration
To apply a conformal coating, there is not necessarily a 'best' way. The method of application chosen for a specific assembly would depend on which existing equipment is available to the manufacturer, the coating processes in use, taking time (the average time period between the start of production of one device and the start of the next one) and the design of the assembly. It encompasses those circuit areas that need to be covered and those that should not be covered (connectors, switches, etc.).
The 'best' method of application will ensure that each board to be coated receives coating coverage at an appropriate thickness on all necessary metal surfaces to protect against the environment. These specifications can vary from board design to board design and environment to environment and must be reviewed and verified before the production run.
Automated Conformal Coating Equipment:
In conformal coating methods, the selective coating will be a more recent phenomenon. Selective coating blends the advantages of multiple methods of the coating into a single method of coating. There are various types of applicators for coating. Spray coating is an atomized method that can achieve a thinner film pass; however, the applicator typically has to move more slowly if selectivity is a requirement. The finish on the edges is a glossy or fuzzy surface.
- Conformal Coating Equipment (Dip):
Automated Dip Coating is one of the most efficient methods of conformal coating application and is ideal for large or small volume production. The method of dipping a circuit board in a conformal coating material stored in a tank helps ensure complete coverage. This also includes underneath the components and around difficult later 3D boards, and there is no over-spray or material wastage.
- Conformal Coating Equipment (Semi-Automated):
In addition to several spray booths, we use a variety of HVLP spray guns for our hand spray process. This approach is suitable for small-to-medium-sized quantities. In addition, this approach is recommended for customers with large components or a geographical layout which does not lend itself to a programmable conformal method of coating.
To sum up
Conformal coating began as a simple process on electronic substrates requiring extra shielding from external elements, with little attention being paid to performance factors beyond adequate coverage of components. Semiconductor assemblies' increased capacity to perform complex tasks in automotive applications, signage, traffic control, outdoor surveillance, and mission-critical elements has boosted the demand for conformal coating.
The reliability of the application of the coating material is critical because system failure could have dire consequences. New equipment and processes are in place to meet these new technologies' conformal coating requirements. Through evaluating the item being coated and the desired result, the coating material used, the chosen process and the economic costs over a period of time, a smooth transition to automated precision conformal coating can be achieved.