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Benefits of conformal coating for PCB & PCBA Assembly

Benefits of conformal coating for PCB & PCBA

It is well known that the performance of PCBs can be affected by many external or environmental factors such as moisture, extreme temperatures, and chemicals. A protective coating is a polymer film applied to the surface of a PCB to protect the PCB and its components from corrosion and environmental contaminants. By protecting against contaminants and environmental factors, protective coatings prevent corrosion of conductors, solder joints, and wiring. In addition, it acts as an insulator, thereby reducing the effects of thermal and mechanical stress on the components.

What are PCBA Standards?

PCB conformal coating is a protective coating that covers the surface of a PCB and is designed to prevent PCB surface components from oxidation, corrosion, contamination, and other effects of the external environment. This coating technology is not only used beyond electrical connections but also for solder-ability coatings and protective layers beyond solder mask coatings. PCB coating is mainly divided into two parts:

What are PCBA Standards

  1. Surface solder mask, commonly known as paint, is used to protect the line, copper surface coating. This coating is generally green, white, black, red, yellow, brown, purple, and other colors.
  2. Surface treatment (such as immersion gold, gold plating, gold fingers, OSP, immersion silver, immersion tin, etc.), used to do PCBA welding, binding, etc.

Types of conformal coating

Depending on the chemical composition, FC‘s protective coatings can be categorized into five types: acrylic, epoxy, polyurethane, silicone, and parylene. The selection of a particular coating is based on the application and electronic requirements of the PCB. Choosing the appropriate material is the only way to protect the PCB effectively.

Acrylic Protective Coating

This is the most commonly used protective coating for PCB. Acrylic Resin (AR) is a preformed acrylic polymer dissolved in a solvent and used to coat PCB surfaces. Acrylic protective coatings can be applied by hand brushing, spraying, or dipping into the acrylic resin coating.

Polyurethane Protective Coating Polyurethane (UR)

The coating provides excellent protection against chemicals, moisture, and abrasion. Polyurethane (UR) protective coatings are easy to apply but difficult to remove. It is not recommended for direct restoration by heat or soldering iron, etc., as it releases the toxic gas isocyanate.

Epoxy Resin (ER type)

Epoxy resins are usually a two-component thermosetting compound. It has excellent conformal properties in harsh environments. It is easy to apply, but can damage circuits when removed.

Silicone (SR type)

Silicone (SR type) protective coatings are used in high temperature environments. These coatings are easy to apply and have low toxicity, and provide protection against abrasion and moisture. Silicone coatings are one-component compounds.

Parylene

Parylene coatings are applied to PCBs using a chemical vapor deposition process. Parylene turns into a gas when heated, and after the cooling process it is placed in a chamber where it polymerizes and turns into a film. The film is then applied to the surface of the PCB.

Considerations for Selecting Conformal Coating Materials

So let’s discuss what conformal coating is best for your PCB. The type of conformal coating required depends on the thickness of the coating required, the area covered, and the degree of adhesion of the coating to the board and its components. Since there are many options when it comes to choosing the right conformal coating for a PCB, there are many factors to consider. Below, we will cover the first three areas to consider when choosing a conformal coating.

Considerations for Selecting Conformal Coating Materials

Product Usage

The first and most critical aspect to consider is the intended use of the product. Matching the advantages and disadvantages of the conformal coating to the use of your product is key to choosing the best PCB conformal coating for your product.

Temperature Range

When determining the type of coating for your product, you should have a clear understanding of the minimum and maximum temperatures that your product will withstand. Temperature range is an extremely important factor to consider. Failure to take this into account can result in damage to the PCB. Below, we will present an example where temperature extremes are critical for the type of coating chosen.
The use of PCBs in airplanes is an example where temperature extremes are an important consideration. Airplanes can encounter extreme temperature ranges while in the air, including -65 degrees Celsius (-85 degrees Fahrenheit), and on the runway it can exceed 100 degrees Celsius (212 degrees Fahrenheit). Silicone coatings are the only option that can be used in this range for long periods.

Environmental Factors

Conformal-coated PCBs may encounter many environmental factors that will help you determine the best conformal coating for your PCB. For example, suppose the PCB will be placed in a partially sealed protective enclosure. In this case, the only environmental factors to consider are condensation and humidity. Below we will list some other common environmental factors that should be considered:

  1. Extreme humidity
  2. Salt spray environments
  3. Corrosive gases
  4. Immersion environments

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