The role and characteristics of three-proof paint

1. What is conformal coating and what are the conformal coatings?

Conformal coating is a specially formulated coating used to protect circuit boards and their related equipment from the environment. Conformal coating has good high and low temperature resistance; After curing, it becomes a transparent protective film, which has superior insulation, moisture-proof, leakage-proof, shock-proof, dust-proof, anti-corrosion, anti-aging, corona resistance and other properties.

Conformal coating has a wide range of applications in the electronics manufacturing industry, and there are acrylic, polyurethane and other different components of conformal paint on the market, conformal coating is also called PCB electronic circuit board protective oil, protective oil, electronic waterproof glue, circuit board coating oil, circuit board moisture-proof paint, conformal coating, insulating paint, anti-corrosion paint, anti-salt spray paint, dustproof paint, protective paint, coating paint, conformal adhesive, etc. So what are the three conformal coatings? It should be said that there is no definition in a strict sense, the word "three" takes the meaning of the ancient word "more", that is, the intention of multi-directional protection, the basic role of conformal coating in daily application is to have waterproof, moisture-proof, dust-proof "three proof" performance, in addition to cold and thermal shock resistance, aging resistance, radiation resistance, salt spray resistance, ozone corrosion resistance, vibration resistance, good flexibility, strong adhesion and other properties, because of its low technical content, low price, widely used in low-end products.

The role of secondary and tertiary conformal coatings

Conformal coating is a specially formulated coating used to protect the circuit board and its related equipment from the environment, so as to improve and extend the life and ensure the safety and reliability of use. Under real-world conditions, such as chemical environment (fuel, coolant, etc.), vibration, high dust, salt spray, humidity and high temperature, etc., the circuit board may cause corrosion, softening, deformation, mildew and other problems, resulting in circuit board failure. Conformal coating is applied to the surface of the circuit board to form a flexible film with a thickness of about 50-100 microns. It protects circuits from damage in relatively harsh conditions.

3. Characteristics of conformal coating

1. One-component, low-viscosity resin, suitable for brushing, spraying, dipping, spraying and other processes, with good adhesion.

2. It has good resistance to high and low temperatures; After curing, it becomes a transparent protective film, which has the properties of insulation, moisture-proof, leakage-proof, shock-proof, dust-proof, anti-corrosion, anti-salt spray, mildew-proof, anti-aging, and corona resistance.

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Fourth, the use of conformal paint

Conformal coating is applied to the surface of the circuit board to form a 50-100 micron thick film. It protects circuits from damage in conditions such as chemicals (e.g., fuels, coolants, etc.), vibration, moisture, salt spray, humidity and high temperatures. Under these conditions, the circuit board can be corroded, mold grows, and short circuits can cause faulty circuits without conformal coatings.

Conformal coating is mainly used in daily applications: color TV, refrigerator, washing machine, microwave oven, air conditioner, telephone, electric water heater and other ordinary household appliances and electronic products integrated circuit protection, with strong adhesion, waterproof, lightning protection, rust prevention, corrosion prevention and other properties, can greatly improve the performance stability of household appliances.

Fifth, the process requirements of conformal coating

(1) Conformal coating construction technology

1. Brushing - the simplest conformal coating process, which can produce an excellent coating effect on a smooth surface.

2. Spraying - 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. Machine spraying can realize automatic feeding, save labor and material costs, improve production efficiency, and ensure product consistency, product quality, and surface spraying effect.

3. Dipping - Dipping ensures complete film overlay, and does not cause material waste due to overspraying.

4. Selective coating - accurate coating and no waste of materials, suitable for large quantities of lamination, but high requirements for coating equipment. Ideal for laminating large quantities. Use a compiled XY table to reduce masking. When painting PCB boards, there are many connectors that do not need to be painted. If the adhesive tape is too slow and there is too much residual glue when tearing, you can consider making a combined cover according to the shape, size and position of the connector, and positioning it with the mounting hole. Cover areas that do not need to be painted.

(2) Precautions during operation

1. Clean and dry the plate to remove moisture and moisture. Dust, moisture and oil stains on the surface of the object to be coated must be removed so that it can fully exert its protective effect. Thorough cleaning ensures that corrosive residues are completely removed and that the conformal coating adheres well to the surface of the board. Baking conditions: 60 °C, 10-20 minutes, take it out in the oven and apply it while it is hot.

2. When applying the conformal coating by brushing, the brushing area should be larger than the area occupied by the device to ensure that the device and pad are fully covered;

3. When brushing the conformal coating, the circuit board should be placed flat as much as possible, and there should be no drip after brushing, and the brushing should be smooth, and there should be no exposed parts, between 0.1-0.3mm.

4. Before brushing and spraying the conformal coating, ensure that the diluted conformal coating is fully 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 viscosity agent or a flow cup), and the viscosity can be adjusted with a diluent.

5. The circuit board assembly should be vertically immersed in the paint residue. 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.

6. When re-using after dipping, if there is crusting on the surface, remove the epidermis and continue to use.

7. After brushing, lay the circuit board flat on the bracket and prepare for curing, and the method that needs to be heated is 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 extra amount of time to allow the solvent to flash out after curing in a high-temperature furnace.

(3) Operating environment requirements
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1. The coating of conformal paint should be carried out in a separate closed room, and there must be good ventilation facilities in the operation room.

2. Smoking, eating, drinking, and drinking are prohibited in the operation room, and alcoholic beverages are not used before work.

3. Wear masks or gas masks, rubber gloves, chemical protective glasses and other protective equipment when operating to avoid harming the body.

4. After the work is completed, the used utensils should be cleaned in time, the tools and equipment should be sorted out and tested, and the lid of the container with conformal paint should be tightly covered.

5. The workplace should be clean and dust-free, no dust flying, and unrelated personnel should be prohibited from entering.

6. Tools and equipment should be fully grounded, and electrostatic protection measures should be taken.

7. Do not place the circuit boards on top of each other during operation; The PCB board should be placed horizontally.

8. Before each batch of raw materials is used, a small sample curing test should be done.

(4) Where conformal paint should not be applied

1. High-power with heat dissipation surface or radiator components, power resistors, power diodes, cement resistors.

2. DIP switches, adjustable resistors, buzzers, battery holders, fuse sockets (tubes), IC holders, and tact switches.

3. All types of sockets, pin headers, terminal blocks and DB headers.

4. Plug-in or stick-type light-emitting diodes, digital tubes.

5. Other parts and devices that cannot be used for insulating paint as specified in the drawings.

6. The screw holes of the circuit board should not be coated with conformal coating.

(5) Requirements for PCB boards coated with conformal coating

1. There should be no paint flowing, dripping and semi-wetting on the surface of the circuit board.

2. The conformal coating layer should be smooth, bright, and uniform in thickness to protect the surface of the pad, adhesive component or conductor.

3. The surface of the paint layer should not have orange peel shape, bubbles, pinholes, and ripples.

4. Devices or components that do not need protection do not need to be brushed with conformal paint.

5. The printed board after the three proofs should be clean and tidy, and there should be no component damage.

6. There are no defects and foreign objects such as dirt, handprints, ripples, shrinkage holes, dust on the board surface and components, and there is no chalking and no peeling.

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Sixth, the difference between conformal coating and PCB nano coating

Although conformal coating also has many characteristics and advantages, can make electronic products have moisture-proof, leakage-proof, shock-proof, dust-proof and other properties, but with the development of science and technology and the increasing improvement of people's material life, consumers have put forward more requirements for the quality of products, people no longer need a simple and crude three-proof products, but to meet more environmental protection, health, lightweight and other aspects of the needs, relevant countries and economies have also improved the supervision of the threshold, access threshold increased, Manufacturing enterprises that use low-end materials to produce low-quality products are facing greater survival challenges, more and more high-end manufacturing industries are aware of this, and continue to invest in research and development, improve quality, and begin to use more advanced and cutting-edge materials and technologies, nano moisture-proof and anti-corrosion coating is the advanced representative of PCB waterproof, moisture-proof and anti-salt spray corrosion materials, nano coating not only has the basic protective characteristics of conformal coating, but also solves some problems that conformal coating can not solve, and greatly improves the protection and environmental performance. As the industry pioneer of PCB nano coating, nano moisture-proof coating has always led the market direction, and its products have been tested by many domestic listed companies.