Used During Rigid Flex PCB
Conformal coating is a thin, protective polymer film that ‘conforms’ to the surface of a printed circuit board. It provides insulation between the board and air-borne contaminants, allowing it to remain electrically insulating over long periods of time. In addition, it also protects against moisture and other environmental hazards such as corrosion.
The type of conformal coating used will vary depending on the type of environment it is subject to and the level of protection required. Typically, the best choice for harsh environments will be polyimide, which is a flexible and thermally stable material that can withstand high temperatures. Other conformal coatings that are suitable include epoxies, urethanes, and silicones. Silicones are especially good for use in corrosive and high-temperature environments.
During the design process for rigid flex pcb, fabricators must consider the materials that will be used to create the circuit boards, as well as the specific components and parts. This will have a direct impact on the assembly process, and it is important that PCB manufacturers consider these considerations at the very beginning of the design phase in order to ensure that both the fabricator and the end-user will be satisfied with the final product.
Conformal coating can be applied in a variety of ways, the most common being spraying. This is usually done using an automated system that is programmable, enabling the conformal coating to be precisely deposited onto the board. This method is popular for high volume assembly and can be very fast and efficient. However, it is necessary to make sure that the entire surface of the PCB is coated as it can be difficult to spot any missed areas.
What Is Conformal Coating and Why Is It Used During Rigid Flex PCB?
Another conformal coating method is dipping. This is a more labor intensive process, but it can be very effective in high volume production. The PCB is first immersed and then withdrawn from the conformal coating solution, allowing the immersion speed, withdrawal speed, and the viscosity of the solution to determine the resulting film formation. It is important that the dipped PCB is carefully inspected after this step to ensure that the conformal coating adheres properly.
It is essential that the PCBs be free of impurities and physical defects before the conformal coating process begins, as any debris will cause uneven adhesion and result in corrosion or short circuits. Humidity testing is particularly important, as humidity in the environment can react with metal components and connections on a circuit board, causing damage or failure. One common adhesion problem, known as ‘fish eyes’, occurs when little craters form on the surface of the conformal coating, due to the spray coating being applied too thickly.
Once the PCB has been coated, it must be cured in order to fully set. The curing process can be controlled by heat, ultraviolet light, or both. Choosing the right process will depend on the type of circuit board, as some require more heat than others. It is also vital to choose the correct solvent for the removal process, as some types of solvents are more sensitive than others. For example, acrylics are very sensitive to solvents, while epoxies and urethanes are less so.