With the globe continuing to witness the miniaturization of circuitry and electronics, the conformal coating PCB seems to have skyrocketed than ever before. To shield a PCB from elements such as moisture, extreme temperatures, and dust, manufacturers apply conformal coatings. Choosing the best type of surface to use is vital.
However, weeding through plenty of information found online is a daunting exercise. But that is not the case anymore in this time and age. In this post, we are going to provide 12 guides on how to go about choosing the ideal conformal coating for your PCB.
Functions of Conformal Coating of a PCB
shielding electronic components from corrosion and environmental elements, the surface also plays other essential roles.
Other roles include acting as an insulative material for a printed circuit board and minimizing environmental stress when assembling a printed circuit board. Conformal coatings are also crucial since they assist in eliminating the need for sophisticated and complex enclosures.
Conformal coatings also ensure a printed circuit board’s longevity by protecting it from fungus, heat, humidity, and airborne contaminants such as dust and dirt.
Classification and Properties
There are several options for conformal coating technologies, with the best option depending on the required protection. Ease of rework and the method of application are also essential factors to be considered. The following are some of the typical classifications of conformal coating:
• Acrylic acid resin – they are excellent at providing general protection and moderate elasticity. It is also recognized based on its moderate moisture resistance and dielectric strength.
• Epoxy resin – apart from creating hard coatings, they also come in two parts. They offer excellent humidity resistance and consist of high chemical and abrasion resistance.
• Organic silicone – this one provides average fungal and moisture resistance. It highly excels at- high-temperature ranges and is good at high vibration tools.
• Polyurethane – this coating is excellent when it comes to chemical and moisture resistance. Additionally, PolyurethanePolyurethane is abrasion and solvent resistant.
• Parylene – this unique type of surface applied through a cured offer high vapor-phase deposition. Apart from its excellent dielectric strength, this type of cover is suitable for working in applications where temperatures are high.
• UV curing coating – UV cured coatings are known for being difficult to repair or rework while coatings that get cured offer fast production throughputs.
Conformal coating choosing principles
To ensure that your PCBs have the right coat of the conformal coating material, you may have to go through a series of selection principles. It will ensure that you find the best of the best material. Here are the selection principles that you need to watch out for:
Single Piece Is Easier To Operate
When selecting conformal coatings, you need to go for unique part components first. Single component conformal coatings mean that the surface requires no need of mixing conformal ingredients before application. Single-component layers are highly preferable based on the fact that they provide both excellent chemical and humidity resistance.
Single-coating components are also one of the best coatings to use because they are easy to apply and that they enjoy a long pot life. The only major drawback regarding single-components is that they need some long curing to achieve optimum care.
Material Cure Mechanism
The cure mechanism is not a primary criterion when choosing the type of surface to use. In the long run, though, it directly impacts the nature of the method of application that will be workable.
There are types of cure mechanisms that are known to be relatively dependable. Simultaneously, some are complicated and leave room for several application errors, mainly when used in uncontrolled environments. Some of the most basic cure mechanisms include:
• UV Cure – here, coatings get cured using ultraviolet light and offer quick production throughputs. Layers cured through UV are a bit challenging to rework and repair.
• Heat Cure –this type of curing is used as part of a secondary UV Cure mechanism, evaporate cure, or moisture cure. Heat Cure is ideal if one cure mechanism cannot meet the required cure properties.
• Moisture Cure – this is a curing used with an evaporative cure.
• Evaporative Cure Mechanism – here, the liquid carrier first evaporates, leaving behind a coating. While somewhat simple in theory, PCBs may have to be dipped not less than two times to ensure a buildup of enough layer on the components’ edges.
Long Shelf Time
Shelf life or product shelf life is the maximum recommended time for a product to last on the shelf. During this time, the defined quality remains, as stated under the stated conditions of display, storage, and distribution. You do not want to purchase products that only last a few days or weeks before going bad.
Among other nuisances that customers often complain about, little shelf life makes it the list of significant problems, especially for customers who prefer goods that will last long. The same is true when it comes to selecting conformal coatings. Some coatings do not come with the promise of long shelf life, hence the need to avoid them if possible. Silicone Conformal Coating 433B is an ideal product, not only for its faster cure time but also for longer shelf life.
Wide Range Of Operating Temperature Range
As you may be aware, plenty of PCB designers are lately squeezing more and more performance out of PCB. Power densities seem to be on the rise, and so are high temperatures with the ability to wreak havoc on dielectrics and conductors. Some PCBs tend to function in high-temperate environments, such as those meant for military-grade applications.
When choosing a conformal coating to use on your PCB, you’ll be in a better position going for materials that can withstand a wide range of operating temperature ranges. The surface should do so without impacting the functionality of the board. For instance, silicone resin is one of the best materials that can offer protection in a wide temperature range.
Engineering or Performance Characteristics
When shopping for a conformal coating to use on your PCBs, its engineering or performance characteristics matter the most. What are its chemical properties? Have you checked whether the surface is resistant to instances of dust and humidity? You do not want to use a layer whose performance on your PCB would be below par.
Before selecting the type of coating to use, make sure that it cannot cause or bring about stress on components, especially during thermal extremes. The surface must have the ability to withstand thermal hot-spots that are produced by components.
Ability to Protect The Board From Extremely High/Low Temperatures And Mechanical Impact
Individual PCBs find substantial use in high-temperate environments such as equipment used in the military. Still, individual PCBs regularly get exposed to situations where the mechanical effect is enormous. You have to ensure that components on the printed circuit board are shielded both from high/low temperatures in addition to high mechanical effects. To achieve this, you’ll have to shop for a conformal coating with such characteristics.
At high or low temperatures, some types of conformal coatings will fail, thereby affecting the functionality of your entire board. The cured coating needs to be abrasion-resistant to withstand constant handling, especially during manufacturing.
The Conformal Coating Should Get Cured at High Speeds Without By-Products Generation
Curing conformal coatings happen immediately after the process of dispense or coating spray is done. The surface is regarded as fully cured when the conformal coating applied on the PCB board is tack-free to get handled.
At times, curing can be accomplished at average room temperature, even though it takes some significant time to dry. Most engineers desire to produce PCBs at high rates for them to realize substantial profit margins. The conformal coating selected must be able to get cured at high-speeds without generating by-products to achieve these profits.
Low Toxicity And Low Cost
As a PCB manufacturer, there’s nothing more dangerous than having to deal with toxic materials that may negatively impact your health. Unfortunately, this scenario is common when manufacturing PCBs. Many PCB firms in business use highly toxic compounds, some of which were banned many years ago. Much worse, some of them use high-cost materials and pass the manufacturing cost to the end customer.
A good conformal coating material, apart from ensuring that it is low-cost and affordable, should be made of non-toxic materials.
Repairability
The conformal coating that you choose to use must be easily repairable or re-workable. Repairability is an aspect that ensures that the solder touches up takes place as desired during component placement. For excellent results, the materials you choose to use for patching must be the same as those used in the initial assembly coating.
Verification Method and Technique
Lastly, when choosing the best conformal coating for your PCBs, you need to ensure that you subject them to verification methods and techniques. Fundamental verification and technique methods include inspection, demonstration, test, and analysis.
Verification will ensure that you get to avoid errors before you begin mass production of your PCBs. You need to ensure that you inspect the conformal coating you use and demonstrate if it can work, test, and analyze using calculations and test models.
Summary
When selecting a conformal coating for your PCB, you need to keep functionality and application requirements at the back of your mind. While it is crucial to protect your PCB, ensuring that you protect it with the right materials is vital.
Unlike other manufacturers, we at WellPCB have a team of experienced personnel that will make your conformal coating selection process stress-free. Out entire coatings are made while employing high-quality standards aimed at ensuring enhanced reliability and optimum performance.
