The role of circuit board anti-proof paint

- Jan 06, 2020-

The role of circuit board anti-proof paint

Tri-proof paint is a specially formulated coating to protect circuit boards and related equipment from environmental damage. Tri-proof paint has good resistance to high and low temperature; after curing, it forms a transparent protective film, which can be used under conditions such as containing chemical substances (such as fuel, coolant, etc.), vibration, humidity, salt spray, humidity and high temperature. Protect the circuit from damage. Under these conditions, the circuit board may be corroded, mold growth, and short circuit, etc., and has excellent insulation, moisture resistance, leakage resistance, dust resistance, corrosion resistance, aging resistance, mildew resistance, anti-looseness, and corona resistance. .


Three anti-paint effect


Moisture is the most common and most destructive factor for PCB circuit boards. 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 patina of the metal part of the PCB circuit board is caused by the chemical reaction of copper, water vapor, and oxygen that are not coated with three anti-paints.


 Apply three anti-paints to printed circuit boards and components. When it may be affected by adverse operating environment factors, it can reduce or eliminate the degradation of electronic operating performance. If such a varnish can maintain its effect for a satisfactory period of time, such as greater than the life of the product, it can be considered as its coating purpose.


Three anti-paint components


Acrylic products


Acrylic tri-proof paint is flexible and can provide comprehensive protection. Because it is a single-component system, it has the characteristics of good adhesion, simple operation, low requirements on equipment and conditions, convenient construction, high transparency, high brightness, short operation cycle, etc., so they are easy to use and easy to remove. Some acrylic products meet military standards. They dry quickly without drying, and can be removed with matching organic solvents. Therefore, this type of circuit board anti-proof paint is one of the most versatile and effective products on the market.


Is the three anti-lacquer toxic?


The toxicity of the three-proof paint depends on the type of thinner and solvent used in the three-proof paint. If the three-proof paint uses toluene or xylene as the diluent, this chemical is harmful to the human body. Smaller. Xylene is moderately toxic, irritating to the eyes and upper respiratory tract, and at high concentrations, it has anesthetic effects on the central system.


Although there are many so-called environmental protection paints on the market nowadays, in actual use, we still need to take protective measures and wear gas masks.


Three anti-painting processes are as follows:


1. Brush painting-widely used, it can produce excellent coating effect on smooth surface.


2. SprayingThe use of spray cans can be easily applied to maintenance and small-scale production. Spray guns are suitable for large-scale production, but these two spraying methods require high accuracy of operation and may produce Shadow (where the lower part of the component is not covered with anti-paint).


3. Automatic dip coating-dip coating can ensure complete coating without material waste caused by excessive spraying.


4. Selective coating film-coating is accurate and does not waste material, suitable for large-scale coating film, but the requirements for coating equipment are high. Most suitable for high-volume lamination. Use a compiled XY table to reduce occlusion. When PCB boards are painted, there are many connectors that do not need to be painted. The adhesive tape is too slow and there is too much adhesive residue when tearing. Consider making a combined cover according to the shape, size and position of the connector, and positioning it with the mounting holes. Cover unused areas.


Three anti-paint operation process requirements


1. Clean and dry the board to remove moisture and moisture. The dust, moisture and oil on the surface of the object to be coated must be removed first so that it can fully exert its protective effect. Thorough cleaning can ensure that the corrosive residues are completely removed, and the three-proof paint adheres well to the circuit board surface. Baking conditions: 60 ° C, 10-20 minutes, it is better to apply the coating while it is hot in the oven;


2. Apply by brushing. The brushing area should be larger than the area occupied by the device to ensure that the device and the pad are completely covered.


3. When painting, the board should be placed as flat as possible. There should be no dew after brushing. The brushing should be flat and there should be no exposed parts.


4. Before brushing and spraying, make sure that the diluted product is fully stirred, and let it stand for 2 hours before brushing or spraying. Use a high-quality natural fiber brush and gently dip it at room temperature. If using machinery, the viscosity of the coating should be measured (using a viscosity agent or flow cup), and the viscosity can be adjusted using a diluent.


5. The circuit board components should be immersed vertically in the paint. Do not immerse the connector. Unless carefully covered, the circuit board should be immersed for 1 minute until the air bubbles disappear, and then slowly take out. A uniform film will form on the surface of the circuit board. Most paint residue should flow from the circuit board back to the dipping machine. TFCF has different coating requirements. The immersion speed of the circuit board or components should not be too fast, so as not to generate excessive air bubbles.


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


7. Lay flat on the stand after brushing and prepare for curing. The heating method is needed to accelerate the curing of the coating. If the surface of the coating is uneven or contains air bubbles, curing in a high-temperature furnace should be allowed to stand at room temperature for more time to allow the solvent to flash out.




1. If a thicker coating is desired, it is best obtained by applying two thinner coatings-and the first layer must be completely dry before the second layer is allowed to be applied.


2. When coating paint on PCB, general connectors, software sockets, switches, heat sinks, heat dissipation areas, and plug-in areas are not allowed to have coating materials. It is recommended to use tearable solder mask.


3. Thickness of the film layer: The thickness of the film layer depends on the application method. A large amount of diluent is added, the viscosity of the glue is low, and the thickness of the glue is thin; otherwise, the viscosity of the glue is high, and the thickness of the glue is thick.


4. All coating operations should be carried out under the condition of not lower than 16 and relative humidity lower than 75%. PCB as a composite material absorbs moisture. If it is not dampened, the three anti-paint can not fully protect. Pre-drying and vacuum drying remove most of the moisture.


 Method for repairing coated devices

If repairing a device that has been coated, simply contact the soldering iron directly to the coating to remove the component. After installing the new component, clean the area with a brush or solvent, then dry and reuse the coating Coated well.

Previous:Analysis of common terms in PCB! Don't be wrong again! Next:Next-generation system design makes packaging and PCB design easier