PCB Tech - Guidelines for choosing the ideal conformal coating for PCBs

As the world continues to witness the miniaturization of circuits and electronic products, conformal coating PCBs seem to have soared more than ever. In order to protect the PCB from factors such as moisture, extreme temperatures, and dust, manufacturers have adopted conformal coatings. Choosing the best type of surface to use is crucial.

However, it is a difficult task to eliminate from the large amount of information found on the Internet. But in this age and age, this is no longer the case. In this article, we will provide 12 guidelines on how to choose the ideal conformal coating for your PCB.

The role of PCB conformal coating

To protect electronic components from corrosion and environmental factors, the surface also plays other important roles.

Other functions include acting as an insulating material for printed circuit boards and minimizing environmental stress when assembling printed circuit boards. Conformal coatings are also important because they help eliminate the need for complex enclosures.

The conformal coating also protects the printed circuit board from fungus, heat, moisture, and air pollutants (such as dust and dirt), thereby ensuring the longevity of the printed circuit board.

Classification and attributes

There are many options for conformal coating technology, and the best choice depends on the protection required. The ease of rework and the method of application are also important factors that need to be considered. The following are some typical classifications of conformal coatings:

• Acrylic resins-They are excellent at providing general protection and moderate elasticity. It is also recognized for its moderate moisture resistance and dielectric strength.

• Epoxy resins-in addition to producing hard coatings, they are also divided into two parts. They have excellent moisture resistance, and have high chemical resistance and abrasion resistance.

• Silicone-This silicone provides average anti-fungal and moisture resistance. It performs well in the high temperature range and is good at high vibration tools.

• Polyurethane-This coating is excellent in chemical resistance and moisture resistance. In addition, polyurethane polyurethane has abrasion resistance and solvent resistance.

• Parylene-This unique type of surface applied by curing provides high vapor deposition. In addition to excellent dielectric strength, this type of cover is also suitable for working in high temperature applications.

• UV-curing coatings-It is well known that UV-curing coatings are difficult to repair or rework, and cured coatings can provide rapid production.

Three anti-paint selection principles

To ensure that your PCB has the correct conformal coating material coating, you may need to follow a series of selection principles. It will ensure that you find the best material. The following are the selection principles you need to pay attention to:

Single piece is easier to operate

When choosing a conformal coating, you need to choose a unique component first. The one-component conformal coating means that the surface does not need to be mixed to maintain constituents before application. Based on the fact that the single-component layer provides excellent chemical resistance and moisture resistance, the single-component layer is very preferred.

Single-coat components are also one of the best coatings to use because they are easy to apply and have a long pot life. The only major disadvantage of single components is that they require a long period of curing to achieve the best care effect.

Material curing mechanism

The curing mechanism is not the main criterion when selecting the type of surface to be used. However, in the long run, it will directly affect the nature of feasible application methods.

Several types of curing mechanisms are known to be relatively reliable. At the same time, some are complex and leave room for multiple application errors, mainly when used in uncontrolled environments. Some of the most basic healing mechanisms include:

• UV curing-here, the coating is cured with UV light and provides fast throughput. Layers cured by UV light are somewhat challenging for rework and repair.

• Thermal curing-This type of curing is used as part of secondary UV curing, evaporation curing, or moisture curing. If a curing mechanism cannot meet the required curing characteristics, thermal curing is the ideal choice.

• Moisture curing-this is a type of curing used with evaporation curing.

• Evaporative curing mechanism-where the liquid carrier evaporates first, leaving the coating behind. Although somewhat simple in theory, the PCB may have to be dipped no less than twice to ensure that sufficient layers are formed on the edge of the component.

Long shelf life

The shelf life or product shelf life is the longest recommended time for the product to be on the shelf. During this period, the defined quality remains unchanged, as described under the prescribed display, storage and distribution conditions. You don’t want to buy a product that will only deteriorate after a few days or weeks.

Among other troubles that customers often complain about, the short shelf life makes it a list of major issues, especially for customers who like products that can be used for a long time. This is also true when choosing a conformal coating. Some coatings do not have a long shelf life promise, so they need to be avoided as much as possible. Silicone Conformal Coating 433B is an ideal product, not only because of its faster curing time, but also a longer shelf life.

Wide operating temperature range

As you may know, many PCB designers are squeezing more and more performance from PCBs recently. Power density seems to be on the rise, and high temperatures can also cause severe damage to dielectrics and conductors. Some PCBs tend to operate in high temperature environments, such as those used in military-grade applications.

When using conformal coatings for use on PCBs, you will be in a better position for materials that withstand various operating temperature ranges. The surface should do so without affecting the function of the circuit board. For example, silicone is one of the best materials and can provide protection over a wide temperature range.

Engineering or performance characteristics

When purchasing a conformal coating for PCB, its engineering or performance characteristics are most important. What is its chemical nature? Have you checked whether the surface can withstand dust and humidity? You don't want to use lower-than-standard layers on the PCB.

Before choosing the type of coating to use, make sure that it does not cause or bring stress to the components, especially under extreme thermal conditions. The surface must be able to withstand the hot spots generated by the component.

Able to protect the circuit board from extremely high/low temperature and mechanical shock

A single PCB is widely used in high-temperature environments, such as military equipment. Nevertheless, individual PCBs are often exposed to huge mechanical effects. In addition to high mechanical effects, you must ensure that the components on the printed circuit board are protected from high/low temperature. For this, you must purchase a conformal coating with these characteristics.

At high or low temperatures, certain types of conformal coatings will fail, thereby affecting the function of the entire circuit board. The cured coating needs to be abrasion resistant to withstand constant handling, especially during the manufacturing process.

Conformal coating should cure at high speed without producing by-products

After finishing the dispensing or coating spraying process, the conformal coating is cured immediately. When the conformal coating on the PCB is non-sticky for processing, the surface is considered fully cured.

Sometimes curing can be done at average room temperature, even if drying takes a long time. Most engineers hope to produce PCBs at a high rate to achieve substantial profit margins. The conformal coating selected must be capable of curing at high speeds without producing by-products to achieve these profits.

Low toxicity and low cost

As a PCB manufacturer, nothing is more dangerous than dealing with toxic materials that may negatively affect your health. Unfortunately, this situation is very common when manufacturing PCBs. Many PCB companies in business use highly toxic compounds, some of which were banned years ago. To make matters worse, some of them use high-cost materials and pass on manufacturing costs to the end customer.

A good conformal coating material, in addition to ensuring its low cost and reasonable price, should also be made of non-toxic materials.

Repairability

The conformal coating you choose to use must be easy to repair or rework. Repairability is an aspect that ensures that solder contacts are made as needed during component placement. In order to achieve excellent results, the material you choose for repair must be the same as the material used in the initial assembly coating.

Verification methods and techniques

Finally, when choosing the best conformal coating for your PCB, you need to make sure that you validate them with methods and techniques. Basic verification and technical methods include inspection, demonstration, testing and analysis.

Verification will ensure that you avoid mistakes before you start mass production of PCBs. You need to make sure to check the conformal coating you use and use calculations and test models to prove that it can work, test, and analyze.

Generalize

When choosing a conformal coating for your PCB board, you need to keep the functional and application requirements in mind. While protecting your PCB is essential, it is also essential to ensure that the correct materials are used to protect it.