Printed circuit boards are extremely susceptible to a wide range of contaminants that can significantly damage or ruin them in a relatively short period of time. These contaminants include moisture, dust, and harmful chemicals. In addition, electronic circuits are also susceptible to extreme temperatures and environments.
Conformal coating provides a protective coating that can significantly reduce or eliminate many of these problems whether the circuitry is used in a relatively peaceful office setting or in an unforgiving industrial factory.
Uses for Conformal Coating
The process is used extensively in conjunction with the manufacture of LEDs, MEMs and printed circuit boards in such diverse industries as medical, automotive and aerospace. Its main use is to prevent the contamination of insulating surfaces by ionic substances such as the oils from human hands and moisture from the environment.
These contaminants interrupt the unfettered flow of electrons through the circuit that ultimately results in degraded accuracy. While a conformal coat will, to a large degree, prevent this “ionic” degradation, it also substantially reduces the effects of mechanical stress due to vibration and also thermally insulates the circuit.
With electronics becoming an increasingly important feature of everyday life, people want to take their electronic devices with them wherever they go. These devices need to be protected from the elements to ensure that they continue to operate effectively.
Liquid conformal coatings can be applied in a variety of ways depending on the needs of the end-user. Here are the most common application methods:
Brushing – Extensively used in repair and low –volume applications, this method is relatively rare as it varies widely in quality depending on the skill of the applicator.
Spraying – This method is an excellent choice for medium-volume applications but only if the substrate is clean and the suitably adhesive.
Dipping – This is the application of choice for almost all high-volume applications however proper preparation is essential as the coating will penetrate all areas of the circuit that are not properly masked.
Robotic – In some instances, a robot may be used to selectively coat circuit boards using several of the above processes. In particular, a robot spraying can vary flow rates, viscosity while spraying and can use varying vacuum pressure to enhance the dipping process.
Curing and Drying
The application of the conformal coating is not the end of the process. To maintain the proper thickness, the coatings must be dried in the appropriate environment and within the proper parameters. Depending on the variation of the coating, sometimes the cure can be over 30 days at room temperature!
Conformal coatings come in water-based and standard solvent formulations. Both are typically and economically air-dried but both applications also lend themselves to accelerated drying through the use of heat or UV sensitive coating formulations.
Why Use Conformal Coating?
The simple fact is that, in many harsh environments, conformal coating is necessary for the printed circuit boards to work with any degree of dependability and longevity. In addition, more benign environments will still degrade the accuracy and efficiency of unprotected circuit boards.
For these reasons, conformal coatings are a necessity for a wide variety of electronic circuits where uninterrupted service on critical equipment is necessary. In fact, the wide variety of conformal coatings available means those end-users can eliminate much of the uncertainty and costs associated with unexpected downtimes and reduce their overall infrastructure and operating costs.