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Does Your PCB Assembly Need Conformal Coating? Solved

conformal coating
pcbonline PCBONLINE Team Wed, Mar 17, 2021

three-anti paint coating

Conformal coating, or urethane coating/polyurethane coating, is applied onto the PCB surface to keep it from moisture, dust, chemicals, and so on when it is assembled. The conformal coating is formulated to protect the printed circuit board (PCB) and important equipment from damage. The specialized spray improves and extends the PCB assembly's life of service, safety, and reliability.

In many cases, PCBs are operating in harsh environments such as high salt, humidity, vibration, and dust. Covered with the conformal coating, the areas of the circuit board that need protection can be effectively isolated.

So it is necessary to apply the conformal coating to your PCB assembly.

What is the Conformal Coating for PCB Assembly

Urethane/polyurethane is a flammable chemical that is usually saved in construction sites or warehouses, away from hot environments and smoke to prevent any fire. When operating, operators should wear masks and gloves for safety reasons. Also, the environment where urethane/polyurethane is stored should have not too much humidity, and it should not be placed near other chemical solvents.

Each printed circuit board design could have different electrical components, which means different conformal coating techniques. Here is how PCBONLINE applies urethane for PCB coating.

Benefits of Conformal Coating

The main benefits of applying a conformal protective coat to the printed circuit boards are mainly to extend their life and ensure that the surface is properly protected from external influences. Also the appearance of the improved PCB, regardless of the color of the protective coat, looks better and ensures proper execution of functionalities under higher temperatures.

Another great benefit of the conformal coating is that it avoids oxidation which can cause a variety of issues. The coating also reduces the occurrence of PCB faults in SMT patch processing and prevents other problems such as insulation between the tin feet of the PCB, short circuits, and anti-static.

Lastly, the conformal coatings can easily prevent dampness, insulation, and static electricity which ensures normal functionality for longer service life.

Here comes a question.

Do all components need urethane spraying?

Some of the components on the surface of the printed circuit board cannot be covered with urethane/polyurethane. For electrical components such as plug-in devices, buttons, connectors, light-emitting diodes, and golden fingers, when using a brush coating, dip, or manual spraying, it is necessary to add masking tape. Even with fully automated selective method equipment, if the coated area is too close to the non-stackable position (usually less than 5 mm), an isolation process is required.

Four Techniques of Applying Conformal Coating

Here are four techniques for applying the conformal coating to the circuit board assemblies.

  • Hand spray or brushing method: the process is low-volume, low-cost, and the operation is simple. The general issue is meeting the thickness and consistency.
    hand spray conformal coating
  • Spraying with a spray gun: it is good for large-volume assemblies. The issue requires the high precision of the operation.
    gun spray conformal coating
  • Automatic coating machine method: It can achieve precise spraying. The spraying head can avoid urethane touching components. And the thickness uniform can be easily ensured.
    automatic coating
  • Selective automatic coating machine method: It is precise and good for large-volume assemblies. It has functions from the irregular continuous curve and three-axis linkages such as live/point/arc/face or circle.
    selective auto coating

How to Apply Conformal Coating to PCB Assembly

The surface of the printed circuit board should be firmly cleaned before the coating process. For products such as aerospace, automotive, military, or marine, where there are strict requirements, the coating can be applied after the PCB is washed and dried. On the other hand for the low requirements, dry high-pressure gas is used to remove any unnecessary matter from the surface of the board or any dust.

Before using the selective automatic coating equipment or machine for mass production, you should pay close attention to the first piece of inspection work. Ensure that there are no reported problems such as less coating, leaking coating, multiple coatings, or air bubbles. The area or device where the coating is denied from being coated cannot adhere and the coating's uniform thickness and baking can be performed.

Lastly, the working environment humidity should be strictly controlled and it should be below 65% RH when the conformal coatings are performed. The printed circuit board can absorb moisture as a composite material.

After the assembly of the circuit, the circuit board should be carried out for spraying urethane as soon as possible. If the printed circuit board is left for a long time it is better to bake again before applying the conformal coating. The baking temperature is about 60 degrees Celsius for 24 hours straight.

Choose PCBONLINE for PCB Assembly and Conformal Coating

PCBONLINE provides a high-quality circuit board assembly one-stop service, which is custom. You can apply the conformal coating to your assembly. We ensure the beautiful outside, thickness, and consistency meet your expectations. PCBONLINE is specialized in advanced circuit boards. Whether your circuits are simple or complex, PCBONLINE can handle the project easily and deliver it to you fast. Want your assemblies to last long and work stably? Click the button below and enjoy the best quality assembly service with free samples and functional testing.

conformal coating PCBA

The conformal coating will achieve the best surface uniformity and protection to the PCBA by electrostatic spraying and then UV thermal setting. We commonly use Perters 1301 and HumiSeal 1A33 for conformal coating. Conformal coating for PCBA samples is free from PCBONLINE. If you need batch PCB assembly with conformal coating and you want discounts, please feel free to contact PCBONLINE by email at info@pcbonline.com. 


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