Three proofing paint is a specially formulated coating used to protect circuit boards and related equipment from environmental erosion. Three proofing paint has good high and low temperature resistance; After curing, it forms a transparent protective film, which can protect the circuit from damage under the conditions of chemical substances (such as fuel, coolant, etc.), vibration, moisture, salt mist, humidity and high temperature. Under these conditions, the circuit board may be corroded, mold growth and short circuit. It has superior properties such as insulation, moisture-proof, anti leakage, dust-proof, anti-corrosion, anti-aging, anti mold, anti part loosening and insulation corona resistance.
Three proofing paint
Moisture is the most common and destructive factor to PCB. Excessive moisture will greatly reduce the insulation resistance between conductors, accelerate high-speed decomposition, reduce Q value, and corrode conductors. We often see that the metal part of PCB circuit board has copper green, which is caused by the chemical reaction of copper, water vapor and oxygen.
When the three proofing paint is coated on the printed circuit board and components, when it may be affected by adverse factors of the operating environment, the deterioration of electronic operating performance can be reduced or eliminated. If the coating can maintain its function for a satisfactory period of time, such as longer than the service life of the product, it can be regarded as having achieved its coating purpose.
Three proofing paint composition
Acrylic acid products
Acrylic three proofing paint has strong flexibility and can provide comprehensive protection. Because it is a single component system, it has the characteristics of good adhesion, simple operation, low requirements for equipment and conditions, convenient construction, high transparency, high brightness and short operation cycle, so they are easy to use and easy to remove. Some acrylic acid products meet military standards. They dry quickly without drying, and can be removed with supporting organic solvents. Therefore, this kind of circuit board three proofing paint is one of the most widely used and effective products in the market.
Is the three proofing paint poisonous
Whether the three proofing paint is toxic depends on the type of diluent and solvent used. If toluene and xylene are used as diluents for the three proofing paint, this chemical is harmful to human body. If lipids and alcohols are used, the harm is small. Xylene is moderately toxic, irritating to eyes and upper respiratory tract, and anesthetic to central system at high concentration.
Although there are many so-called environmental protection three proof paints in the market, in actual use, it is still necessary to take protective measures and wear gas masks when using.
There are four application processes of three proofing paint:
1. Brush coating – it is widely used and can produce excellent coating effect on smooth surface.
2, spraying – spray tank products can be easily applied to maintenance and small-scale production and use. Spray guns are suitable for large scale production, but these two spraying methods require higher accuracy in operation and may cause shadows.
3. Automatic dip coating – dip coating can ensure complete coating without material waste caused by overspray.
4. Selective coating – coating is accurate and does not waste materials. It is suitable for large quantities of coating, but has high requirements for coating equipment. It is most suitable for large quantities of film coating. Using a prepared XY table can reduce masking. When painting PCB boards, many connectors do not need painting. The adhesive tape is too slow and there is too much residual adhesive when tearing. Consider making a combined cover according to the shape, size and position of the connector and positioning it with the installation hole. Cover areas not to be painted.
Operation process requirements of three proofing paint
1. Clean and dry the board to remove moisture and moisture. The dust, moisture and oil stain on the surface of the object to be coated must be removed first, so that it can give full play to its protection effect. Thorough cleaning can ensure that the corrosive residues are completely removed and the three anti paint is well adhered to the surface of the circuit board. Drying plate conditions: 60 ° C, 10-20 minutes. After taking it out of the oven, the coating effect is better when it is hot;
2. The brush coating method shall be used, and the brush coating area shall be larger than the area occupied by the device, so as to ensure that all devices and pads are covered;
3. When brushing, the plate shall be placed flat as far as possible. There shall be no drip after brushing. The brushing shall be flat and there shall be no exposed part, preferably between 0.1-0.3mm.
4. Before brushing and spraying, ensure that the diluted product is fully stirred and placed for 2 hours before brushing or spraying. Use a high-quality natural fiber brush and gently brush and dip at room temperature. If machinery is used, the viscosity of the coating shall be measured (with viscosity agent or flow cup), and the viscosity can be adjusted with diluent.
5. The circuit board assembly shall be immersed vertically in the coating tank. Do not immerse the connector unless it is carefully covered. Immerse the circuit board for 1 minute until the bubbles disappear, and then take it out slowly. A uniform film will be formed on the surface of the circuit board. Most of the paint residue shall be allowed to flow back to the film dipping machine from the circuit board. TFCF has different coating requirements. The immersion speed of circuit board or components should not be too fast to avoid too many bubbles.
6. When re-use after dip coating, if there is skin on the surface, remove the skin and continue to use.
7. After brushing, place it flat on the support to prepare for curing. The method that needs to be heated is to accelerate the curing of the coating. If the coating surface is uneven or contains bubbles, it shall be cured in a high-temperature furnace for more time at room temperature to allow the solvent to flash out.
matters needing attention:
1. If a thicker coating is desired, it is best to obtain it by applying two thinner coatings – and the second coating is allowed only after the first layer is completely dry.
2. When coating PCB, coating materials are not allowed for general connectors, software sockets, switches, radiators, heat dissipation areas, plug-in board areas, etc. it is recommended to use tear proof welding glue to cover them.
3. Film thickness: the film thickness depends on the application method. The addition of diluent is large, the viscosity of glue is low, and the thickness of glue is thin; On the contrary, the viscosity of glue is high and the thickness of glue is thick.
4. All coating operations shall be carried out at a temperature of not less than 16 ℃ and a relative humidity of less than 75%. PCB as a composite material will absorb moisture. If the moisture is not removed, the three proofing paint can not fully play a protective role. Pre drying and vacuum drying can remove most of the moisture.
Method for repairing coated device
If the coated components are repaired, the components can be removed only by directly contacting the welding iron with the coating. After installing new components, clean the area with brush or solvent, then dry and re coat with coating.