What is PCBA conformal coating why need coating

Conformal coating (common film) is a specially formulated coating used to protect circuit boards and related equipment from environmental erosion. The three-proof paint has good resistance to high and low temperature; it forms a transparent protective film after curing, which has excellent insulation, moisture resistance, leakage resistance, shock resistance, dust resistance, corrosion resistance, aging resistance, corona resistance and other properties.

Definition

What is the Conformal coating?

Conformal coating are called according to the requirements and focus of each region and each manufacturer, such as three anti-glue, moisture-proof glue, insulating glue, moisture-proof paint, protective paint, protective paint, coating glue, coating glue , Waterproof glue, moisture-proof oil, three-proof oil, three-proof agent, protective agent, moisture-proof agent, conformal coating, conformal coating, conformal coating, common coating, the English name is Conformal Coating. Three anti-paint is a kind of specially formulated paint, used to protect circuit boards and related equipment from environmental erosion, thereby increasing and prolonging their service life, ensuring the safety and reliability of use.

Under realistic conditions, such as chemical, vibration, high dust, salt spray, humidity and high temperature, the circuit board may have corrosion, softening, deformation, mildew and other problems, which may cause the circuit board to malfunction. The three-proof paint is coated on the surface of the circuit board to form a layer of three-proof protective film (three-proof refers to anti-moisture, anti-salt spray, and anti-mildew). Under conditions such as chemical substances (for example: fuel, coolant, etc.), vibration, humidity, salt spray, humidity and high temperature, the circuit board that is not used with the three-proof paint may be corroded, mold growth and short circuit, etc., leading to the circuit In the event of a failure, the use of three-proof paint can protect the circuit from damage, thereby improving the reliability of the circuit board, increasing its safety factor, and ensuring its service life. In addition, because the three-proof paint can prevent leakage, it allows higher power and closer printed board spacing. Thereby, the purpose of miniaturization of components can be met.

PCBA Conformal coating is also known as: PCBA protective oil, PCBA waterproof glue, PCBA insulating paint.

It has three functions of waterproof, moisture-proof and dust-proof to PCBA.

 

1.What are the coating methods for PCBA Conformal coating?

1) Impregnation

It is more economical for large-scale equipment, but the thickness after coating will be affected by factors such as immersion temperature, time, extraction speed, vertical flow time, and whether to add an air knife.

2) Spraying

It is more economical for small and medium-sized equipment. When spraying is used, it is like spraying paint. The uniformity of coating depends on the relative moving speed, spraying position, spraying pressure, and whether there are higher parts.

In addition, the bottom of the part cannot be sprayed, and additional treatment may be required.

3) Brushing

It is more economical for small equipment. When coating, it is easy to cause uneven coating due to the skill and proficiency of coating. In addition, pay attention to the problem of hair brushing. The bottom of the part is also difficult to coat.

4) Selective coating

Although coating has many benefits, it is often time-consuming and labor-intensive. You can also choose to coat where you need it.

2.What tools are needed to apply PCBA Conformal coating?

Conformal coating;

Paint box

Rubber gloves;

Masks or gas masks;

brush;

American tape

tweezers;

Ventilation equipment;

Drying rack

oven.

3.What are the technical requirements for PCBA coating?

Before applying the three-proof paint, make sure that the PCBA has been tested, inspected, and thoroughly cleaned;

The used brush should be kept clean and it is forbidden to use it for other operations; when the brush is painted, be careful not to drip to the part that does not need to be painted; after use, the brush should be cleaned with thinner, etc.;

The coating layer should be transparent, and evenly cover the PCB board and components, with uniform color and consistency;

The process steps are: painting side A → surface drying → painting side B → curing at room temperature;

Spraying thickness: The spraying thickness is 0.1mm~0.3mm;

All coating operations should be carried out under the conditions of no lower than 16℃ and relative humidity lower than 75%. PCB as a composite material will absorb moisture. If it does not remove moisture, the three-proof paint cannot fully protect it. Pre-drying and vacuum drying Most moisture can be removed.

4.What are the process requirements for PCBA coating?

1) Clean and bake the board to remove moisture and moisture

Before brushing, the dust, moisture and rosin on the surface of the PCBA board to be brushed must be removed, so that the three-proof paint adheres to the surface of the circuit board well.

Drying plate conditions: 60°C, 30-40 minutes, take it out of the oven and apply it while it is hot. The effect is better.

2) According to the product size and the layout of the board components, choose the correct brush to use, pour the three-proof paint into the container, and then use the brush to glue the appropriate glue to evenly brush the circuit board.

3) The brushing area should be larger than the area occupied by the device to ensure that the device and the pad are fully covered;

4) When brushing, the PCBA board should be placed as flat as possible. After brushing, there should be no dripping, and the brushing should be flat and there should be no exposed parts. The thickness of the brushing should be between 0.1-0.3mm.

5) After brushing, the plug-in components are placed horizontally on the air-drying rack with one side up and surface dry curing (heating method can accelerate the curing of the coating).

6) When applying three-proof paint on the PCB, all connectors, sockets, switches, radiators (sheets), heat dissipation areas, etc. (not to be painted with three-proof paint components, see remarks) are not allowed to be painted with three-proof paint , Use masking paper to cover and protect when painting.

7) If a thicker coating is desired, it can be obtained by applying two thinner coatings (it is required that the second layer is allowed to be applied only after the first layer is completely dried).

5.What are the operating requirements for PCBA coating?

The conformal coating work should be carried out in a separate enclosed room, and the operation room must have good ventilation facilities;

Smoking, eating, drinking, and drinking are prohibited in the operation room, and alcoholic beverages should not be used before work;

Wear masks or gas masks, rubber gloves, chemical protective glasses and other protective equipment during operation to avoid injury to the body;

After the work is completed, clean the used utensils in time, arrange and test tools and equipment, and cover tightly the container with the three-proof paint;

The workplace should be clean and dust-free, and there should be no flying dust, and irrelevant personnel should be prohibited from entering;

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

Do not overlap PCBA during operation, PCB board should be placed horizontally;

Before using each batch of raw materials, a small sample curing test (3~5PCS) should be done.

6.What are the quality requirements for PCBA coating?

The surface of the PCB must be free of paint, dripping, or semi-wetting;

The three anti-paint layer should be smooth, bright, uniform in thickness, and protect the surface of pads, pasted components or conductors;

The surface of the paint layer must not have orange peel, bubbles, pinholes, or ripples;

There is no need to brush the three-proof paint on the parts or components that do not need protection;

The printed board after the three preventions should be clean and tidy, and there should be no damage to the components;

There are no defects such as dirt, fingerprints, ripples, shrinkage holes, dust, etc. and foreign objects on the board and components, no chalking, no peeling phenomenon.

7.What are the storage requirements for PCBA coating?

Raw materials should be stored in a cool and dry warehouse (the room temperature should not exceed 30 degrees), with explosion-proof ventilation systems and equipment installed, and should be kept away from heat sources;

It should be stored separately from other types of chemicals, and must have clear material identification, and avoid mixed storage;

Pay attention to fire prevention and equip fire-fighting equipment;

The storage warehouse should be equipped with leakage emergency equipment and reasonable storage materials (such as sand);

The warehouse should be ventilated to prevent accidents caused by the accumulation of leaking gas;

The effective date of use should be indicated on the storage container;

Storage racks or equipment should be well grounded, and equipment and tools that are prone to sparks are prohibited.

8.What are the precautions for applying PCBA Conformal coating?

The use of three anti-paints beyond the shelf life is prohibited;

The storage container should be kept tightly closed after opening;

It is forbidden to pour the remaining three-proof paint back into the original storage container, and keep it separately and airtight;

If the working room or storage room is not opened for a long time (more than 12 hours), it should be ventilated for 15 minutes before entering;

If you accidentally spill the glasses, open the upper and lower eyelids immediately, rinse them with running water or normal saline, and then seek medical treatment;

If you feel uncomfortable when brushing, you should leave the work site to a place with fresh air quickly. Give oxygen when breathing is difficult, and then seek medical attention.

9.Which PCBA components cannot be coated with conformal coating?

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

Dip switch, adjustable resistance, buzzer, battery holder, insurance holder (tube), IC holder, touch switch;

All types of sockets, pin headers, terminal blocks and DB headers;

Plug-in or paste-type light-emitting diodes, digital tubes;

Other parts and devices that are not allowed to use insulating paint specified in the drawings;

The screw holes of PCBA boards cannot be painted with conformal paint.

10.Application

Typical uses include the following ranges:

1.Civil and commercial applications

Three-proof paint (common film) can provide protection for electronic circuits in household appliances, so that they can resist:

(1) Water and detergent (washing machine, dishwasher, bathroom products, outdoor electronic LED screen)

(2) Unfavorable external environment (display screen, anti-theft, fire alarm device, etc.)

(3) Chemical substance environment (air conditioner, dryer)

(4) Harmful substances in offices and homes (computers, induction cookers)

(5) All other circuit boards that need three-proof protection

2.Automobile industry

The automobile industry requires the three-proof paint to protect the circuit from the hazards of the following situations, such as: gasoline vapor, salt spray/brake fluid, etc. The application of electronic systems in automobiles continues to grow rapidly, so the use of three anti-paints has become a basic requirement to ensure long-term reliability of automobile electronic devices.

3.Aerospace

Due to the particularity of the use environment, the aviation and aerospace environments have strict requirements on electronic equipment, especially under the conditions of rapid pressurization and decompression, still maintaining good circuit performance. Therefore, the pressure stability of the three anti-paints has been widely used.

4.Nautical

Whether it is fresh fresh water or salty seawater, it will cause harm to the electrical circuits of ship equipment. The use of three-proof paint can maximize the protection of the equipment on the water surface and even the submerged and underwater equipment.

5.Medical

The three-proof paint can protect electronic equipment from external chemical agents and special use environments to ensure its continuous stability.

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