Protect Your PCBA With Conformal Coating

Protect Your PCBA With Conformal Coating

PCBAs are vulnerable to many types of damage and degradation. Conformal coating is one method to protect components and exposed copper on a PCB from corrosion and other damage.

The type of coating used and its application determine its effectiveness. There are five main conformal coatings in use today; acrylic, silicone, epoxy, urethane and parylene.

Water Resistance

PCBs can be damaged by various factors, including moisture, corrosion, dust, and chemical contaminants. This can lead to a variety of failure modes, which require costly repairs. A conformal coating prevents these contaminants from reaching the internal components of a PCB, keeping it safe for its intended lifetime.

Moisture is the biggest cause of corrosion on a PCB, but a good conformal coating will counteract this issue by creating an insulating layer that keeps moisture from contacting metal components and connections. This is important because if a metal contacts moisture it will create an electrochemical reaction that causes oxidation, which leads to the formation of conductive tree-like metallic filaments called dendrites.

A conformal coating protects against this by shielding the circuit from contact with moisture, which will also reduce abrasion and shock damage. The insulating properties of a conformal coating can be measured using Surface Insulation Resistance (SIR) testing.

There are five main types of conformal coating currently in use for electronic applications: acrylic, epoxy, urethane, silicone, and parylene. Each has different attributes and serves a unique purpose. For example, silicone has a high dielectric strength and can handle extreme temperatures, while acrylic is affordable, durable, and flexible. For PCBs that will be in harsh environments, urethane is an excellent option because it can withstand salt spray and resist corrosion from standard chemicals.

Chemical Resistance

With modern commercial and industrial systems becoming more dependent on electronic components, it is important to have them functioning correctly in varying climatic conditions. Humidity, dust, corrosion, and solder flux residues are all factors that can cause a system to malfunction and eventually fail. Conformal coatings are designed to physically protect and electrically insulate printed circuit board assemblies (PCBAs) from these environmental stresses, thus extending their lifespan and reliability.

PCBAs can be coated PCBA Coating with acrylic, epoxy, urethane, or parylene. Acrylic is the most common, with a good level of performance, but lacks the specialized capabilities that some of the other types can provide.

Solder residues left over after hand, reflow, or wave soldering can attract moisture and cause corrosion of component leads and PCBA contacts. These residues can also interact with metal ions to initiate electrochemical reactions that result in oxidation at anodic conductors and reduction at cathodic conductors. This is a type of failure mode called electrochemical migration and can lead to catastrophic shorting of conducting lines across closely spaced components.

A conformal coating protects the exposed copper and components on a PCBA from degradation by these environmental effects, however, it must be applied correctly to ensure this protection. Prior to coating, the PCBA must be cleaned thoroughly. Any voids, holes, or spaces should be filled to prevent the coating from seeping into these areas and contaminating them. Via holes must be tented to prevent the coating from flowing through them and potentially affecting the integrity of the circuit board.

Corrosion Resistance

Conformal coating provides corrosion resistance to PCBs to ensure they can operate for their intended lifetime. Unlike general purpose varnishes and shellacs, conformal coating is designed specifically for PCBs and components to deliver a robust protective shield that prevents damage from chemical degradation. Conformal coatings are typically tested for performance in a variety of environmental conditions to ensure they can meet industry standards and end-use requirements.

In uncoated PCBAs, corrosion can occur when the solder flux residues oxidize and form metal ions. When the ions drift towards anodic conductors and encounter a DC voltage bias, they may cause electrochemical migration and lead to short circuit failure [1]. Conformal coating PCB manufacturer suppresses this metal migration by providing a barrier to the penetration of corrosive chemicals, salt, and moisture.

Moreover, conformal coating resists microbial growth to prevent the decomposition of polymers and other materials that can deteriorate the physical and electrical properties of the coating. This is particularly important for PCBAs that will be subjected to high humidity, tropical temperatures or contact with soils that are prone to microorganisms.

Selective conformal coating can be applied to a PCB using either a spray applicator or dip process. This method is a cost-effective solution for high volume applications and allows the user to choose the specific areas of the board that require protection. Unlike potting and encapsulation resins, conformal coating can be removed easily for rework or repair. This flexibility makes it an ideal option for rapid prototyping and high volume production electronics.

Electrical Resistance

Conformal coatings add an effective layer of dielectric protection to a PCBA, preventing the electrical issues that would otherwise arise from moisture damage and corrosion. As well as reducing the risk of ECM, they also prevent the formation of dendrites and other types of short circuit. They also offer improved Surface Insulation Resistance (SIR) that protects against failure modes like corrosion, fungal growth and electrostatic discharge (ESD).

In addition to moisture and corrosion resistance, conformal coatings have excellent chemical resistance as well. Harsh chemicals such as salt spray and standard oxidation have difficulty penetrating the protective layer of the coating, meaning that even when used in harsh environments like ocean or desert conditions, assemblies will last much longer in the field before deterioration.

As a flexible polymeric film, a conformal coating can adapt to the shape of the board and components it covers, giving it its ‘conformal’ nature. Some areas of the assembly may require to be left uncoated, for example connectors and mounting holes used for grounding. To avoid these areas being coated, masking can be applied prior to the spray process.

As a manufacturer, Electrolube puts all of its conformal coatings through extensive internal testing to ensure that they meet the required specifications for each individual application. As a result, many of the coatings in our Konform range are qualified to military standards such as MIL-I-46058C and/or IPC-CC-830B. Full technical data sheets for each product are available from our downloads page.

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