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PCB Tech

PCB Tech

PCB Tech

PCB Tech

PCB conformal coating standard
2021-09-03
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Author:Belle

PCB three-proof paint is also called PCB protective oil, PCB waterproof glue, and PCB insulating paint. Because it has three functions of waterproof, moisture-proof and dust-proof on PCB, it is called "PCB three-proof paint".
 
What are the coating methods for PCB conformal paint?
1. Dipping: It is more economical for large-scale equipment, but the thickness after coating will be affected by factors such as dipping temperature, time, extraction speed, vertical flow time, whether to add an air knife or not.
2. Spraying: More economical for small and medium-sized equipment. When spraying is used, it is just 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 brush lint. The bottom of the part is also more difficult to coat.
4. Selective coating (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.
 
What tools are needed to coat PCB three-proof paint?
Three anti-paints, paint boxes, rubber gloves, masks or gas masks, brushes, American tape, tweezers, ventilation equipment, drying racks, ovens.
 
What are the technical requirements for coating PCB tri-proof paint?
1. The protection of the three-proof paint must be tested, inspected and thoroughly cleaned before PCB assembly.
2. 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 parts that do not need to be painted; after use, the brush should be cleaned with thinner.


3. The coating layer should be transparent and cover the and components evenly, with uniform color and consistency.
4. The process steps are: painting side A → surface drying → painting side B → curing at room temperature
5. Spraying thickness: The spraying thickness is 0.1mm—0.3mm
6. All coating operations should be carried out under the conditions of not lower than 16℃ and relative humidity lower than 75%. PCB as a composite material will absorb moisture. If it is not removed, the three-proof paint cannot fully protect it. Pre-drying and vacuum drying can remove most of the moisture.
 
What are the process requirements for coating PCB three-proof paint?
1. Clean and bake the board to remove moisture and moisture. Before brushing, the dust, moisture and rosin on the surface of the PCB 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 full coverage of the device and pads.
4. When brushing, the PCB board should be placed as flat as possible. After brushing, there should be no dripping. 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 the three-proof paint on the PCB, all connecting components, 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 the three-proof paint Yes, use masking paper to cover and protect when painting.
7. If you want to get a thicker coating, 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).

PCB board

 
What are the operating requirements for coating PCB three-proof paint?
1. The three-proof work should be carried out in a separate enclosed room, and the operation room must have good ventilation facilities.
2. Smoking, eating, drinking, and drinking are prohibited in the operating room, and alcoholic beverages should not be used before work.
3. Wear masks or gas masks, rubber gloves, chemical protective glasses and other protective equipment during operation to avoid injury to the body.
4. After the work is finished, clean the used utensils in time, arrange and test tools and equipment, and cover tightly the container with the three-proof paint.
5. The workplace should be clean and dust-free, and there should be no flying 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 overlap PCBA during operation; PCB boards should be placed horizontally.
8. Before using each batch of raw materials, a small sample curing test (3-5PCS) should be done.
 
What are the quality requirements for coating PCB three-proof paint?
1. The surface of the PCB must not have paint flow, dripping, or semi-wetting.
2. The three-proof paint layer should be flat, bright, uniform in thickness, and protect the surface of the pads, pasted components or conductors.
3. The surface of the paint layer must not have orange peel, bubbles, pinholes, or ripples.
4. There is no need to brush the three-proof paint on the parts or components that do not need protection.
5. The printed board after the three proofings should be clean, tidy and free of component damage.
6. There are no dirt, fingerprints, ripples, shrinkage holes, dust and other defects and foreign objects on the board and components, no chalking, no peeling phenomenon.
 
What are the storage requirements for coated PCB tri-proof paint?
1. The 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.
2. It should be stored separately from other types of chemicals, and must have clear material identification, and avoid mixed storage.
3. Pay attention to fire prevention and equip fire-fighting equipment.
4. The storage warehouse should be equipped with leakage emergency equipment and reasonable storage materials (such as sand).
5. The warehouse should be ventilated to prevent accidents caused by the accumulation of leaking gas.
6. The effective date of use should be indicated on the storage container.
7. Storage racks or equipment should be well grounded, and equipment and tools that are prone to sparks are prohibited.
 
What are the precautions for coating PCB three-proof paint?
1. The use of the three-proof paint exceeds the shelf life and is forbidden to use.
2. The storage container should be kept tightly closed after opening.
3. It is forbidden to pour the remaining three-proof paint back into the original storage container, and keep it separately and tightly.
4. 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.
5. If you accidentally splashed into the glasses, open the upper and lower eyelids immediately, rinse them with running water or saline, and then seek medical treatment.
6. 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 treatment.
 
Which PCB components cannot be coated with conformal paint?
1. High-power belt cooling surface or radiator components, power resistors, power diodes, cement resistors.
2. Dip switch, adjustable resistance, buzzer, battery holder, insurance holder (tube), IC holder, touch switch.
3. All types of sockets, pin headers, wiring terminals and DB headers.
4. Plug-in or paste-type light-emitting diodes and digital tubes.
5. Other parts and devices that are not allowed to use insulating varnish specified in the drawings.
6. The screw holes of the PCB  board cannot be painted with conformal paint.