The function and characteristics of three-proof paint

1. What is conformal paint, and what is conformal paint?

Conformal paint is a specially formulated coating used to protect circuit boards and their associated equipment from environmental aggression. Conformal paint has good high and low temperature resistance; It is cured into a transparent protective film, which has superior insulation, moisture-proof, leakage-proof, shockproof, dustproof, anti-corrosion, anti-aging, corona resistance and other properties.

Conformal paint has a wide range of applications in the electronic manufacturing industry, and there are also acrylic, polyurethane and other different components of conformal paint, conformal paint is also called PCB electronic circuit board protection oil, protective oil, electronic waterproof glue, circuit board coating oil, circuit board moisture-proof paint, conformal coating, insulation paint, anti-corrosion paint, anti-salt spray paint, dust-proof paint, protective paint, coating paint, conformal adhesive, etc. So what exactly is the conformal paint? It should be said that there is no strict definition, the word "three" takes the meaning of the ancient word "many", that is, the intention of multi-directional protection, the basic role of conformal paint in daily application is to have waterproof, moisture-proof, dustproof "three-proof" performance, in addition to cold and heat 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.

2. The role of the three-proof paint

Conformal coatings are specially formulated coatings to protect circuit boards and their associated equipment from bad conditions, thereby improving and extending their lifespan and ensuring safety and reliability of use. Under real conditions, such as chemical environment (fuel, coolant, etc.), vibration, high dust, salt spray, humidity and high temperature, the circuit board may cause corrosion, softening, deformation, mildew and other problems, resulting in circuit board circuit failure. Conformal paint is applied to the surface of the circuit board, forming a flexible film with a thickness of about 50-100 microns. It protects circuits from damage under relatively harsh conditions.

3. Characteristics of conformal paint

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

2. It has good high and low temperature resistance; After curing, it forms a transparent protective film, which has the properties of insulation, moisture-proof, leakage-proof, shockproof, dustproof, anti-corrosion, anti-salt spray, anti-mildew, anti-aging, and corona resistance.

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4. The use of conformal paint

Conformal paint is applied to the surface of the circuit board, forming a 50-100 micron thick film. It protects circuits from damage such as chemicals (e.g., fuel, coolant, etc.), shock, moisture, salt spray, humidity and high temperatures. Under these conditions, the circuit board may be corroded, mold growing, and short circuits may occur, leading to failures in circuits without conformal paint.

Conformal paint is mainly used in daily applications to protect the integrated circuits of ordinary household appliances and electronic products such as color TVs, refrigerators, washing machines, microwave ovens, air conditioners, telephones, electric water heaters, etc., with strong adhesion, waterproof, lightning protection, rust resistance, corrosion prevention and other properties, which can greatly improve the performance stability of household appliances.

5. Process requirements for conformal paint

(1) Conformal paint construction technology

1. Brushing - the simplest conformal paint process, which can produce excellent coating results on smooth surfaces.

2. Spraying - spraying method is the most commonly used coating method in the industry, and is divided into two types: automatic spraying by machine and manual spraying. Machine spraying, realize automatic feeding, save labor and material costs, improve production efficiency, ensure product consistency, product quality, and surface spraying effect.

3. Dip coating - Dip coating ensures complete lamination without material waste caused by overspraying.

4. Selective coating film - accurate coating and no waste of materials, suitable for large batches of lamination, but high requirements for coating equipment. It is most suitable for laminating large quantities. Use a compiled XY table to reduce occlusion. When painting the PCB board, 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 mounting holes. Cover the parts that do not need to be painted.

(2) Precautions during operation

1. Clean and dry the board to remove moisture and moisture. The dust, moisture and oil on the surface of the object to be painted must be removed first so that it can fully exert its protective effect. Thorough cleaning ensures that corrosive residues are completely removed and allows the conformal paint to adhere well to the board surface. Baking plate conditions: 60°C, 10-20 minutes, take it out of the oven and apply it while it is hot;

2. When applying conformal paint by brushing method, the brushing area should be larger than the area occupied by the device to ensure that all the devices and pads are covered;

3. When brushing and applying conformal paint, the circuit board should be laid flat as much as possible, and there should be no drip after brushing, and the brushing should be flat, and there should be no exposed parts, which should be between 0.1-0.3mm.

4. Before brushing and spraying the conformal paint, ensure that the diluted conformal paint is thoroughly stirred and left for 2 hours before brushing or spraying. Use a high-quality natural fiber brush and gently brush the dip at room temperature. If using machinery, the viscosity of the coating should be measured (with a viscosity agent or flow cup), and the viscosity can be adjusted with a diluent.

5. The circuit board assembly should be vertically immersed in the paint dregs. The connector should not be immersed unless carefully covered, and the circuit board should be immersed for 1 minute until the bubbles disappear, then slowly removed. A uniform film layer is formed on the surface of the circuit board. Most of the paint residue should flow from the circuit board back to the dipping machine. The circuit board or components should not be immersed too quickly to avoid excessive bubbles.

6. When using again after dipping, if there is a crust on the surface, remove the epidermis and continue to use it.

7. After brushing, lay the circuit board flat on the bracket and prepare for curing. If the coating surface is uneven or contains bubbles, it should be placed at room temperature for more 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 application of conformal paint should be carried out in a separate closed room, and the operation room must have good ventilation facilities.

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

3. Wear a mask or gas mask, rubber gloves, chemical protective glasses and other protective equipment during operation to avoid injury to the body.

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

5. The workplace should be clean and dust-free, free of dust, and irrelevant 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) Places where conformal paint cannot be coated

1. High-power band heat dissipation surface or heat sink element, power resistor, power diode, cement resistor.

2. DIP switch, adjustable resistor, buzzer, battery holder, safety holder (tube), IC holder, tactile switch.

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

4. Plug-in or stick-on light-emitting diode and digital tube.

5. Other parts and devices that cannot use insulating paint as specified in the drawings.

6. The screw holes of the circuit board and board cannot be painted with conformal paint.

(5) PCB board requirements coated with conformal paint

1. The surface of the circuit board should not have flowing paint, dripping, or semi-wetting.

2. The conformal paint layer should be flat, bright, and uniform in thickness, and protect the surface of the pad, sticker components or conductors.

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

4. Conformal paint does not need to be applied to devices or components that do not need protection.

5. The printed board after the three-proof should be clean and tidy, and there should be no damage to components.

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

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6. The difference between conformal paint and PCB nanocoating

Although conformal paint also has many characteristics and advantages, which can make electronic products have moisture-proof, leakage-proof, shockproof, dust-proof and other performances, 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. Manufacturing enterprises that use low-end materials to produce low-quality products face 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 coatings are advanced representatives of PCB waterproof, moisture-proof and salt spray corrosion materials, nano-coatings not only have the basic protective characteristics of conformal paints, but also solve some problems that conformal coatings cannot solve, greatly improving protection and environmental protection performance, As an 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.