What is three-proof paint? The role and types of three-proof paint

What is conformal coating? Conformal coating in different regions and manufacturers, according to the use requirements and focus of the surface has many names, such as three-proof adhesive, moisture-proof adhesive, insulating glue, moisture-proof paint, protective paint, protective paint, coating glue, coating glue, waterproof glue, moisture-proof oil, three-proof oil, three-proof agent, protective agent, moisture-proof agent, conformal coating, conformal coating, common coating, etc., its English name is Conformal Coating. Conformal coating is a specially formulated coating that protects circuit boards and their related equipment from environmental attack, thereby enhancing and extending their service life and ensuring safety and reliability in use.

Under realistic conditions such as chemistry, vibration, high dust, salt spray, humidity and high temperature, the circuit board may have problems such as corrosion, softening, deformation, and mildew, resulting in circuit failure. Conformal coating is applied to the surface of the circuit board to form a protective film with moisture-proof, salt-spray-proof and mildew-proof functions. In the case of containing chemicals (such as fuel, coolant, etc.), vibration, moisture, salt spray, humidity and high temperature, the circuit board without conformal coating may be corroded, breed mold and short circuit, etc., resulting in circuit failure, while the use of conformal coating can protect the circuit from damage, improve the reliability of the circuit board, increase its safety factor and ensure its service life. In addition, conformal coating prevents leakage, allowing for higher power and closer PCB spacing, thus meeting the need for component miniaturization.

Conformal coating classification What are the types of conformal coating? Conformal paint is also known as PCB electronic circuit board protective oil, coating oil, moisture-proof paint, conformal coating, waterproof adhesive, insulating paint, anti-corrosion paint, anti-salt spray paint, dustproof paint, protective paint, coating paint, conformal adhesive, etc., which are classified as follows: From the perspective of chemical composition, conformal coating can be divided into acrylic, silicone, polyurethane conformal coating; In terms of curing methods, there are solvent-based curing, room temperature curing, thermal curing and ultraviolet curing.

<!--[if !supportLists]-->1.<!--[endif]-->Solvent-containing acrylic resin conformal coating (the most widely used popular product in the market at present) Features: fast surface drying and curing time, good conformal performance, low price, transparent color, flexible texture and easy repair.

<!--[if !supportLists]-->2.<!--[endif]-->Solvent-free acrylic resin conformal coating Features: Through UV curing, it can be dried in a few seconds to more than ten seconds, the color is transparent, the texture is hard, and the chemical corrosion resistance and wear resistance are also very good.

<!--[if !supportLists]-->3.<!--[endif]-->Polyurethane conformal coating features: brittle texture and excellent solvent resistance. In addition to superior moisture resistance, it has stable performance in low temperature environments.

<!--[if !supportLists]-->4.<!--[endif]-->Silicone conformal coating This is a soft elastic coating material that relieves pressure well, is resistant to high temperatures of 200 degrees, and is easy to repair.

In addition, from the comprehensive consideration of price and performance, the above-mentioned types of conformal coatings will have a crossover phenomenon, such as silicone modified conformal coatings.

Conformal coating Why do PCB circuit boards need to use conformal coating? Conformal coating is also known as PCB electronic circuit board protective oil, coating oil, moisture-proof paint, three-proof coating, waterproof glue, insulating paint, anti-corrosion paint, anti-salt spray paint, dustproof paint, protective paint, coating paint, three-proof adhesive, etc., the PCB circuit board that has used the three-proofcoating has waterproof, moisture-proof, dust-proof "three-proof" performance, as well as cold and thermal shock resistance, aging resistance, radiation resistance, salt spray resistance, ozone corrosion resistance, vibration resistance, good flexibility, strong adhesion and other properties.

Moisture is the most prevalent and most damaging major factor for PCB circuit boards. Excessive moisture can dramatically reduce the insulation resistance between conductors, accelerate high-speed decomposition, lower Q, and corrode conductors. We often see patina on the metal part of the PCB circuit board, which is caused by the chemical reaction between the uncoated conformal coating metal copper and water vapor and oxygen.

The hundreds of contaminants that can be found on printed circuit boards are just as damaging. They can cause the same results as moisture erosion – electronic decay, corroded conductors and even irreparable short circuits. The most common contaminants in electrical systems can be chemicals left over from the manufacturing process, such as fluxes, solvent release agents, metal pellets, and marking inks. There are also groups of contamination mainly caused by human care, such as human oil, fingerprints, cosmetics and food residues. There are also many contaminants in the operating environment, such as salt sprays, sand, fuels, acids and other corrosive vapours and mold.

The application of conformal coatings to printed circuit boards and components can reduce or eliminate the degradation of electronic performance when they may be affected by adverse factors in the operating environment. If the coating can maintain its effect for a satisfactory period of time, such as longer than the useful life of the product, the purpose of application can be considered to have been achieved.

Even if the coating is thin, it can withstand mechanical vibrations and oscillations, thermal shock, and operation at high temperatures to a certain extent. Of course, it would be a mistake to think that thin films give mechanical strength or sufficient insulation to individual parts inserted into a printed circuit board. The components must be mechanically inserted and have their own suitable caulk in order to have double insurance against accidents.

Conformal Coating Process 01 Brushing Method of Conformal Coating Operation Process The brushing method is the simplest coating method. It is usually used for local repairs and repairs, but can also be used in laboratory environments or small batch trial production/production, and is generally suitable for occasions where coating quality is not required. The advantages of the brushing method are: almost no investment in equipment fixtures; It can save coating materials; Generally, there is no need for a masking process. Its disadvantages are: narrow scope of application; Minimal efficiency; There is a masking effect when the whole board is brushed, the coating consistency is poor, and due to the manual operation, it is easy to have defects such as bubbles, ripples, and uneven thickness; It takes a lot of manpower.

▶ Precautions: Make sure the diluted product is fully stirred before brushing, and it is best to leave it for 2 hours. The container for conformal coating should be made of metal or plastic, not wood or PVC, because it will cause a chemical reaction, corrode the container and destroy the product. To clean and dry the plates, remove moisture and moisture. Dust, moisture and oil must be removed from the surface of the object to be coated, and a thorough cleaning ensures that the corrosive residue is completely removed so that the conformal coating adheres well to the surface of the PCB. The choice of brush is also important, as the product is not insulating before curing, so choose a brush that is anti-static and does not shed, such as a high-quality natural fiber brush. When brushing, the plate should be laid flat as much as possible, and there should be no dew after brushing, and the brushing should be flat, and there should be no exposed parts, and 0.1 - 0.3mm is appropriate. The brushed circuit board should not be placed upside down, otherwise the coating will be thin at the top and thick at the bottom, and it should still be placed flat.

02 Dipping method of conformal coating operation process Dipping coating method has been widely used since the beginning of the coating process, and is suitable for occasions that require complete coating; In terms of coating effect, dip coating is one of the most effective methods. The advantage of the dip coating method is that it can be applied manually or automatically. Among them, the manual operation is simple and easy, and the investment is small; High material transfer rate, which can completely coat the entire product without masking effect; Automated dip coating equipment can meet the needs of high-volume production. The disadvantages of the dip coating method are: if the coating material container is open, there will be impurity problems with the increase of coating times, the material needs to be replaced regularly and the container needs to be cleaned, and the solvent volatilization also needs to be continuously replenished; The coating thickness is too large, and a lot of material will be wasted due to trickle flow after the circuit board is extracted; The area needs to be covered; Masking/removing coverings requires a lot of manpower and material resources; The coating quality is difficult to control and the consistency is poor; Too much manual handling can cause unnecessary physical damage to the product. The main points of the dipping method are: the loss of solvent should be monitored by a density meter at any time to ensure a reasonable ratio; It is necessary to control the immersion and extraction speed to obtain a satisfactory coating thickness and reduce defects such as bubbles; It should be operated in a clean environment with controlled temperature/humidity to avoid affecting the adhesion of the material; Adhesive-free and anti-static masking tape should be chosen, and if normal tape is chosen, a deionized blower must be used.

▶ Precautions for dip coating method: The PCB assembly should be immersed vertically in the paint tank. Do not immerse the connector unless it is carefully covered, the circuit board should be immersed for 1 minute until the air bubbles disappear, and then slowly take it out. A uniform film is formed on the surface of the PCB. Most of the paint residue should be allowed to flow back from the board back to the impregnation machine. The circuit board or components should not be immersed too quickly to avoid excessive air bubbles. If there is crusting on the surface after dipping and re-application, remove the epidermis and continue to use it.

03 Spraying method of conformal coating operation process Spraying method is the most commonly used coating method in the industry, which is divided into two types: automatic spraying by machine and manual spraying. Among them, machine automatic spraying is suitable for customers with large-scale production, large quantities or long-term production. Its advantages are: selective spraying, high accuracy, uniformity, high efficiency, and automatic detection. The disadvantages are: high cost, high requirements for operational accuracy, and the possibility of shading (where the lower part of the component is not covered with conformal coating). The manual spraying is generally a combination of hand-held spray gun + air hose + air compressor (+ exhaust fan). The advantages are: low cost, suitable for medium-sized customers. However, it takes more than 5KG pressure to form a fog barrier, so the adjustment of air pressure is required, if the air pressure is not high, the conformal paint will not be atomized, it will be drawn, and the accuracy of manual spraying is also relatively high. Hand can spraying is also a type of manual spraying, using spray can type products, suitable for maintenance and small-scale production, the biggest advantage is convenience. In short, manual spraying has a small investment and is easy to operate; The coating consistency of machine automatic spraying is good, the production efficiency is the highest, it is easy to realize online automatic production, it is suitable for large and medium mass production, its consistency and material cost are usually better than the dipping coating method, although the masking process is also required, but the requirements are not as high as the dipping method.

The corresponding disadvantages are: the need for a masking process; There is a lot of waste of materials; Requires a lot of manpower; Poor coating consistency, which may have a masking effect, making it difficult to coat underneath narrow-pitch components.

04 Coating method of conformal coating operation process Coating method is a less commonly used conformal coating method. The conformal coating, which is stored in a high tank, is poured down through a nozzle or narrow slit and drenched on the coated object driven by the conveyor in the form of a curtain to form a uniform coating film. The excess conformal coating flows back into the container and is pumped into a high-level tank for recycling. In small batch production, manual operation is generally used to directly pour conformal paint on the product, so the coating method is also called the paint pouring method. In large-scale production, automatic assembly line operation is generally adopted, and the thickness of the conformal coating film on the product is controlled by adjusting the size of the nozzle or the width of the narrow slit. If the coating film is thick, bubbles will appear on the coating film on the product coming out of the conveyor belt through the drying box; If the coating film is thin, the product will appear exposed and unevenly coated. Therefore, the coating method is also called curtain coating. According to the characteristics of different products, in order to increase the adhesion of the conformal coating film on the product, it is sometimes necessary to add sulfur; In order to increase the thickness of the product, it is more necessary to coat and sulfurize the product once or several times.

Conformal coating operation process requirements

<!--[if !supportLists]-->1.<!--[endif]-->Clean and dry the plate to remove moisture and moisture. Dust, moisture and oil must be removed from the surface of the object to be coated so that it can fully protect. Thorough cleaning ensures that corrosive residues are completely removed and that the conformal coating adheres well to the surface of the board. Drying conditions: 60°C, 10 - 20 minutes, remove in the oven and apply while hot for better results.

<!--[if !supportLists]-->2.<!--[endif]-->When applying by the brush coating method, the brush area should be larger than the area occupied by the device to ensure that the device and pads are fully covered.

<!--[if !supportLists]-->3.<!--[endif]-->When brushing, the plate should be laid flat as much as possible, and there should be no dew after brushing, and the brushing should be flat, and there should be no exposed parts, and 0.1 - 0.3mm is appropriate.

<!--[if !supportLists]-->4.<!--[endif]-->Before brushing and spraying, make sure that the diluted product is well stirred and leave for 2 hours before brushing or spraying. Using a high-quality natural fibre brush, apply the dip coat gently at room temperature. If machinery is used, the viscosity of the paint should be measured (with a viscometer or flow cup), and the viscosity can be adjusted with a diluent.

<!--[if !supportLists]-->5.<!--[endif]-->The PCB assembly should be vertically immersed in the paint tank. Do not immerse the connector unless it is carefully covered, the circuit board should be immersed for 1 minute until the air bubbles disappear, and then slowly take it out. A uniform film is formed on the surface of the PCB. Most of the paint residue should be allowed to flow back from the board back to the impregnation machine. TFCF has different coating requirements. The circuit board or components should not be immersed too quickly to avoid excessive air bubbles.

<!--[if !supportLists]-->6.<!--[endif]-->If there is crusting on the surface after dipping and re-application, remove the epidermis and continue to use it.

<!--[if !supportLists]-->7.<!--[endif]-->After brushing, it is placed flat on the bracket and is ready to cure, which requires the heating method to accelerate the curing of the coating. If the coating surface is uneven or contains air bubbles, it should be left at room temperature for an additional amount of time to allow the solvent to flash out before curing in a high-temperature furnace.

Precautions

<!--[if !supportLists]-->1.<!--[endif]-->If you want a thicker coating, it's best to get it by applying two thinner coats – and the requirement is that the first layer is completely dry before the second coat is allowed.

<!--[if !supportLists]-->2.<!--[endif]-->When applying paint to the PCB, it is recommended to use tear-off solder mask to cover the PCB, such as connectors, software sockets, switches, heat sinks, heat dissipation areas, and plug-in board areas.

<!--[if !supportLists]-->3.<!--[endif]-->Thickness of the film: The thickness of the film depends on the application method. The amount of thinner added is large, the viscosity of the glue is low, and the thickness of the glue is thin; On the contrary, the viscosity of the glue is high, and the thickness of the glue is thick.

<!--[if !supportLists]-->4.<!--[endif]-->All coating operations should be carried out at a minimum of 16°C and a relative humidity of less than 75%. PCB as a composite material will absorb moisture, if it does not go to moisture, the conformal coating can not give full play to the protective effect. Pre-drying, vacuum drying removes most of the moisture.

<!--[if !supportLists]-->5.<!--[endif]-->Conformal coatings are used in a wide range of applications. In consumer electronics, such as mobile phones, tablets, etc., the internal PCB circuit board is small in size and dense in components. These devices may be used in a variety of environments, such as water vapor erosion in humid environments, and circuit failures in high-temperature environments. The use of conformal coating can effectively protect these delicate circuit boards and ensure the normal operation of the equipment. For example, in some waterproof mobile phones, although the case has a certain waterproof design, the conformal coating on the internal circuit board is also an important guarantee to prevent moisture from entering the circuit.

<!--[if !supportLists]-->6.<!--[endif]-->In the field of automotive electronics, the electronic control system of the car is becoming increasingly complex and contains a large number of PCB circuit boards. Cars are subject to vibrations, dust, different temperatures and humidity environments, etc. Conformal coating can provide reliable protection for automotive electronic circuit boards to prevent circuit corrosion and failure caused by salt spray, moisture and other factors. For example, the use of conformal coatings for circuit boards in engine control units (ECUs) can prevent damage to circuits caused by high temperatures, oil contamination and water vapor in the engine compartment.

<!--[if !supportLists]-->7.<!--[endif]-->In terms of industrial control equipment, such as automated production equipment and monitoring equipment in factories, these equipment usually need to run stably for a long time. The industrial environment in which they operate may be chemical, dusty, etc. Conformal coatings help protect the circuit boards in these devices, improve the stability and reliability of the equipment, and reduce the cost of equipment repair and replacement due to environmental factors.

<!--[if !supportLists]-->8.<!--[endif]-->In the military and aerospace sectors, the reliability of electronic equipment is extremely demanding. Military equipment and aerospace vehicles may face extreme environmental conditions when performing their missions, such as low temperature and low pressure at high altitudes, high salt spray environment at sea, etc. Conformal coatings ensure that the circuit boards in these devices work properly in harsh environments, ensuring the smooth operation of military operations and aerospace missions.

<!--[if !supportLists]-->9.<!--[endif]-->From the perspective of market development trends, with the continuous miniaturization and high performance of electronic products and the increasing complexity of the use environment, the demand for conformal coatings is also growing. On the one hand, rising consumer expectations for the durability and reliability of electronic products are prompting manufacturers to pay more attention to the protection of circuit boards, thereby increasing the use of conformal coatings. On the other hand, the development of emerging technology areas such as the Internet of Things, 5G communications, etc., has produced a large number of new electronic devices that also require conformal coatings to protect their circuit boards.

<!--[if !supportLists]-->10.<!--[endif]-->However, there are some challenges in the use of conformal coatings. For example, different types of conformal coatings have their own advantages and disadvantages in performance, and how to choose the right conformal coating according to specific application scenarios is a problem that needs to be carefully considered. On some circuit boards with high flexibility requirements, if you choose a brittle polyurethane conformal coating, the paint film may crack when the board is bent or subjected to vibration. Moreover, in some high-precision electronic equipment, the coating process of conformal coating is very strict, if the coating is uneven or the thickness is not appropriate, it may affect the performance of the circuit or heat dissipation effect. In addition, with the increasingly stringent environmental protection requirements, the environmental performance of conformal coatings has also become an important consideration. Some traditional solvent-based conformal coatings volatilize organic solvents during use, which can have an impact on the environment and the health of operators. Therefore, the research and development of environmentally friendly, high-performance conformal coating and the improvement of the coating process will be an important direction for the development of the conformal coating industry in the future.