A Comprehensive Guide To Conformal Coating

Posted on 9th January 2023

A printed circuit board is the heart of all modern electronic devices. 

For any device to function optimally, the PCB must be of the highest standards. And this can only be ensured by following the best practices for PCB assembly. The demand for miniaturised electronics with higher voltage applications has made it necessary for manufacturers to produce PCBs with better insulation, increased performance and reliability. An essential step in the assembly process after soldering that ensures the printed circuit board is well protected and hence, more reliable and efficient, is applying conformal coating. 

Although a newly manufactured PCB generally performs well, its quality and performance can swiftly deteriorate due to external environmental factors. Conformal coating is one of the best ways of protecting printed circuit boards from exposure to environmental elements like moisture, dust, chemicals, salt spray, temperature extremes, vibrations, etc. Here’s everything you need to know about it.

What Is Conformal Coating?

A conformal coating is a lightweight polymeric film applied to printed circuit boards to protect them from corrosion and harmful environmental conditions and increase their longevity. The term conformal refers to the way the coating “conforms” to the irregular surface of a PCB and increases its dielectric resistance, operational efficiency, and reliability. It is applied at 25-250 mm to cover and protect solder joints, electronic component leads, exposed traces, and other metallised areas on the circuit board. 

Types of Conformal Coatings

Conformal coatings are semi-permeable and typically consist of a resin base that has been diluted with a solvent or in some cases, water. Based on the resin base used, the different types of conformal coatings are as follows:

Acrylic Coating

  • Cost-effective and easy to apply
  • Good adhesion
  • Fast drying
  • Good protection against mist, moisture, and dust at a wide operational temperature range   Limited solvent-resistance
  • Limited protection against chemical erosion

Polyurethane Coating

  • Great protection against chemical erosion, even under harsh conditions
  • Excellent protection against moisture
  • Great flexibility at very low temperatures
  • Good abrasion resistance
  • Commonly used within the military or aerospace applications
  • Long curing time

Hybrid Coating

  • A solvent-based coating that combines different chemical bases to create a tailored coating for the required application
  • Enhanced temperature endurance 
  • High chemical resistance
  • More efficient than standard silicone coatings

Silicon Coating

  • High flexibility
  • Highest temperature resistance
  • Easily processed
  • Good dielectric strength and insulation
  • Limited protection against moisture and corrosion

Water-Based Coating

  • Cures by evaporation of water from the system
  • Reduced solvent use
  • Good chemical resistance
  • Low odour and VOC emissions
  • Enhanced environmental and operator safety

UV-Cure Coating

  • A type of hybrid single-layer coating which cures very quickly under exposure to UV light
  • Applied using specialist spray equipment
  • Quickest curing time
  • Good chemical resistance
  • Good temperature resistance
  • Limited flexibility

2K Coating

  • A type of hybrid coating that combines the best properties of encapsulation resins with a conformal coating
  • Cost-effective 
  • Easily processed
  • Thicker than single-layer coatings
  • Enhanced protection against moisture
  • High performance even in harsh environments

Application & Curing

The correct application and curing of conformal coating are just as essential as choosing the right coating type. A poorly applied coating will fail to provide the protection required for the PCB to perform to the highest standards. There are various methods of applying conformal coating, such as:

  1. Manual Brush Coating - A low-cost process that involves the manual application of the coating using a brush. It requires great precision and expertise from the people applying the coating and is only suitable for low-volume application, finishing and repair.
  2. Manual Spraying - Coating is applied with an aerosol can or handheld spray gun. Again, the process requires great manual precision and expertise and is typically used for low-volume production when advanced equipment is not available.
  3. Automated Spraying - This method involves a programmed spray system that moves PCBs on a conveyor under a reciprocating spray head that applies the conformal coating. 
  4. Selective Coating - Often considered the most efficient coating process, it involves the application of the coating using an automated, programmable spray system with a robotic spray nozzle that selectively sprays specific areas on the PCB. It does not require masking before application and is the preferred method for high-volume production. 
  5. Dipping - This process requires masking before the application of the conformal coating and is one of the most popular methods used for this purpose. The circuit board is immersed and then withdrawn from the conformal coating solution. The quality of the film formed after dipping is determined by the immersion speed, withdrawal speed, immersion time, and viscosity. It is mainly used when both sides of the board need coating and is ideal for high-volume assembly. 

Curing is also a crucial step in the conformal coating application process. It can be done using different methods like:

  1. Heat/Evaporation Curing - This process involves applying heat to accelerate the evaporation of the solvent in solvent-based coatings.
  2. UV Curing - It involves using intense UV light to set off a chemical reaction within the coating and cure almost immediately in areas exposed to UV radiation.
  3. Moisture Curing - Used primarily in silicone and some polyurethane systems, this process relies on moisture from the atmosphere to cure. The process can be accelerated by using humidifiers to increase the humidity in the environment. 

Alan Anderson Manufacturing follows the best practices for the application and curing of conformal coating to produce high-performing, reliable and durable PCBs for all kinds of electronic devices. We also use the best testing methods to check the efficiency and quality of the conformal coating applied to protect the PCBs. To find out more about our process and dedication to providing comprehensive, integrated and cost-effective strategies to our customers at component, sub-assembly and finished product levels, contact us on 0333 322 7222. 

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