Triple proof paint is a specially formulated coating used to protect circuit boards and related equipment from environmental erosion. Three anti – paint has good resistance to high and low temperature; After curing, it forms a transparent protective film, which can protect the circuit from damage in the case of chemical substances (e.g. fuel, coolant, etc.), vibration, moisture, salt spray, humidity and high temperature. In these conditions, the circuit board may be corroded, mold growth and short-circuit, etc., with superior insulation, moisture-proof, anti-leakage, dustproof, anti-corrosion, anti-aging, mildew proof, anti-loose parts and insulation corona resistance.
Three anti – paint effect
Moisture is the most common and destructive factor on PCB. Excessive moisture can significantly reduce insulation resistance between conductors, accelerate rapid decomposition, reduce Q values, and corrode conductors. We often see that the metal part of PCB gets verdigris because of the chemical reaction of copper with water vapor and oxygen without coating.
Coating printed circuit boards and components with tri-proof paint can reduce or eliminate the deterioration of electronic performance when it may be affected by adverse operating conditions. If the coating lasts for a satisfactory period of time, e.g. longer than the life of the product, the purpose of the coating is considered to have been achieved.
Three anti – paint components
Acrylic acid product
Acrylic tri-resistant paint is flexible and provides comprehensive protection. As it is a single component system, with good adhesion, simple operation, not high requirements for equipment and conditions, convenient construction, high transparency, high brightness, short operating cycle and other characteristics, so they are easy to use and easy to clear. Some acrylic acid products meet the military standards, they dry quickly and do not dry, can be used to remove the organic solvent matching, so this kind of circuit board three anti-paint is the most widely used and one of the most effective products on the market.
Is the paint toxic
Whether the paint is toxic depends on the type of thinner and solvent used. If the paint is diluted with toluene and xylene, the chemical is harmful to human body. If the paint is diluted with lipids and alcohols, the harm is less. Xylene is moderately toxic and stimulates the eyes and upper respiratory tract. In high concentration, it has anesthetic effect on the central system.
Although there are a lot of so-called environmental protection three anti-paint on the market now, but in the actual use, we are still necessary to do a good job of protection measures, wearing a gas mask when using.
Three anti – paint using process has the following four
1. Brush coating — widely used to produce excellent coating effect on a smooth surface.
2. Spraying — spray can products can be easily used for maintenance and small-scale production. Spray guns are suitable for large-scale production, but these two spraying methods require higher accuracy in operation and may produce shadows (the lower part of components is not covered with three anti-paint).
3. Automatic dip coating — Dip coating can ensure complete coating, and will not cause material waste caused by excessive spraying.
4, selective coating film — accurate coating and no waste of materials, suitable for large quantities of film, but high requirements for coating equipment. The most suitable for large quantities of film mulch. Use a compiled XY table to reduce masking. Many connectors do not need to be painted when PCB is painted. Adhesive paper is too slow and there is too much residual adhesive when tearing, can consider according to the shape, size, position of the connector, do a combined cover, with the installation hole positioning. Cover areas that need not be painted.
Three anti – paint operation process requirements
1. Clean and bake the board to remove moisture and moisture. Dust, moisture and grease must be removed from the surface of the object to allow it to be fully protected. Thorough cleaning ensures that corrosive residues are completely removed and that the tri-paint is well adhered to the circuit board surface. Drying board conditions :60°C, 10-20 minutes, after taking out in the oven, the coating while hot is better;
2. Use brush coating method, the brush coating area should be larger than the area occupied by the device, to ensure that all the devices and pads are covered;
3. The board should be as flat as possible when the brush is applied. There should be no dew after the brush is applied.
4. Make sure the diluted product is thoroughly stirred before brushing or spraying, and let stand 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 paint should be measured (with viscosity agent or flow cup), the viscosity can be adjusted with diluent.
5. Circuit board components shall be vertically immersed in the paint pot. Connectors should not be immersed. Unless carefully covered, the circuit board should be immersed for 1 minute until the bubbles disappear and then slowly removed. A uniform film layer will form on the surface of the circuit board. Allow most of the paint residue to flow back from the circuit board. TFCF has different coating requirements. Immersion speed of circuit board or components should not be too fast, so as not to produce too many bubbles.
6. If there is crust on the surface after dipping, remove the skin and continue to use.
7. After brushing, lay it flat on the bracket for curing. The method requiring heating is to accelerate curing of the coating. If the surface of the coating is uneven or contains bubbles, solidification in a high temperature furnace should be placed at room temperature for a longer time to allow the solvent to flash out.
Matters needing attention
1. If a thicker coating is desired, it is better to obtain it by applying two thinner coatings — and the second coating must be allowed only after the first layer has been completely dried.
2. When coating the PCB, the general connector, software socket, switch, radiator, heat dissipation area, insert board area and so on are not allowed to have coating material, it is recommended to use tear resistant welding glue to cover.
3. Thickness of the film: The thickness of the film depends on the application method. The amount of diluent added is large, the viscosity of the glue is low, the thickness of the glue is thin; On the contrary, the viscosity of the glue is high, the thickness of the glue.
4. All coating operations shall be carried out under the conditions of no less than 16℃ and relative humidity less than 75%. PCB as a composite material will absorb moisture. If not to the tide, three anti – paint can not fully play a protective role. Pre-drying and vacuum drying can remove most of the moisture.
Method of repairing the coated device
If the coated device is repaired, the component can be removed by directly contacting the coating with the soldering iron. After installing the new component, the area should be cleaned with a brush or solvent, then dried and recoated with paint.