PCBA three-proof paint general process

PCBA conformal coating is an extremely important means of protection in the field of electronic manufacturing, and has an irreplaceable and important role. It aims to improve the moisture-proof, mildew-proof and dust-proof performance of PCBA boards, enhance stability and durability, and ensure the stable operation of electronic equipment in various harsh environments. In the whole operation process of PCBA conformal coating, there are strict regulations on all aspects such as process specifications, quality requirements, storage and precautions. The process specification contains the basic content such as the scope of operation, the use of materials and tools, and clarifies the technical requirements, such as the conditions for inspection, cleaning, and drying before painting, the steps of painting and curing in the painting process, and the treatment methods for different components. In terms of operational requirements, it pays attention to the safety and independence of the working environment, emphasizing personnel protection and the correct use and maintenance of equipment and tools.

"PCBA Conformal Coating General Process Specification".

 1. Content and scope of application This operating procedure clearly stipulates the operation specifications, process requirements and quality requirements of all types of PCBA board brushing conformal coatings of the company.

 2. Materials and tools to be used: conformal paint, paint box, rubber gloves, masks or gas masks, brushes, adhesive tape, tweezers, ventilation equipment, drying racks, ovens.

3. Technical requirements

Conformal coating protection must be tested, inspected and thoroughly cleaned before PCBA assembly.

The brushes used should be kept clean and should not be used for other operations; When painting the brush, care should be taken to avoid dripping into the parts that do not need to be painted; After use, the brush should be cleaned with thinner, etc.

The coating layer should be transparent, evenly covering the PCB board and components, and uniform in color and consistency.

The process steps are: painting surface A→ surface dry→ painting surface surface → curing at room temperature.

喷涂厚度：0.1mm - 0.3mm。

All coating operations should be carried out at a minimum of 16°C and a relative humidity of less than 75%. Since PCB is a composite material, it will absorb moisture, if it does not go to moisture, the conformal coating can not give full play to the protective effect, and pre-drying and vacuum drying can remove most of the moisture. Fourth, the process requirements for brushing conformal paint

Clean and dry the plate to remove moisture and moisture. Before brushing, the dust, moisture and rosin on the surface of the PCBA board must be cleaned up, so that the conformal coating can be well attached to the surface of the circuit board. Drying conditions: 60°C, 30 - 40 minutes, remove from the oven and apply while hot for better results.

According to the size of the product and the layout of the board components, the brush is correctly selected, the conformal paint is poured into the container, and then the brush is dipped in an appropriate amount of glue to evenly brush the circuit board.

The brushing area should be larger than the area occupied by the device to ensure complete coverage of the device and pads.

When brushing, the PCBA 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, and the thickness of brushing should be 0.1 - 0.3mm.

After brushing, the side with more plug-in elements is placed horizontally upwards on the air-drying rack for surface curing (the coating can be accelerated by heating).

When applying conformal paint to the PCB, all connected plug-in devices, sockets, switches, radiators (pieces), heat dissipation areas, etc. (see remarks for non-conformal coating components) are not allowed to be brushed, and masking paper should be used to cover and protect them.

If you want to get a thicker coating, you can do this by applying two thinner coats (the first layer must be completely dried before the second coat is allowed). 5. Operational requirements

The three-proof work should be carried out in a separate closed room, and the operation room must have good ventilation facilities.

Smoking, eating, drinking, and drinking are prohibited in the operation room, and alcoholic beverages are not consumed before work.

Wear protective equipment such as masks or gas masks, rubber gloves, and chemical protective glasses when operating to avoid physical injury.

After the work is completed, the used utensils should be cleaned in time, the tools and equipment should be sorted and wiped, and the container with conformal paint should be covered tightly.

The workplace should be clean and dust-free, free of dust, and unrelated personnel should be prohibited from entering.

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

Do not place the PCBA on top of each other during operation; The PCB board should be placed horizontally.

EACH BATCH OF RAW MATERIALS SHOULD BE SUBJECTED TO A SMALL SAMPLE CURING TEST (3 - 5PCS) BEFORE USE. Sixth, quality requirements

There should be no flow paint, dripping and semi-wetting on the surface of the PCB.

The conformal coating layer should be smooth, bright, and uniform in thickness, which can protect the surface of pads, adhesive components or conductors.

The surface of the paint layer should not have orange peel shape, bubbles, pinholes, and ripples.

Devices or components that do not require protection do not need to be conformal coated.

The printed board after the three proofs should be clean and tidy, and there should be no component damage.

There are no defects and foreign substances such as dirt, handprints, corrugations, shrinkage holes, dust and other defects on the board surface and components, and there is no chalking and peeling. 7. Storage requirements The purpose of storage requirements is to ensure the safe storage of raw materials and prevent risks caused by improper storage. The precautions are to give countermeasures for special situations that may occur, such as the treatment of expired paint, the emergency treatment of splashing into the eyes, etc. These comprehensive and detailed regulations help the smooth development of PCBA conformal coating spraying, improve the protective performance of PCBA boards, and ensure the stable operation of electronic equipment in complex environments.

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

It should be stored separately from other types of chemicals, and there should be clear material identification, and it should not be mixed.

Pay attention to fire prevention and be equipped with fire-fighting equipment.

Storage warehouses should be equipped with leakage response equipment and reasonable containment materials (e.g., sand).

The warehouse should be ventilated to prevent the accumulation of leakage gases and cause accidents.

The expiration date should be indicated on the storage container.

Storage shelves or equipment should be well grounded, and it is forbidden to use equipment and tools that are prone to sparks. 8. Precautions

Conformal coating is beyond the shelf life and is forbidden to be used.

The storage container should be kept tightly closed after opening.

It is forbidden to pour the remaining conformal paint back into the original storage container, and it should be stored separately and sealed.

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

If it accidentally splashes into the eyes, immediately open the upper and lower eyelids, rinse them with running water or saline, and then seek medical treatment.

If you feel unwell when brushing, you should quickly leave the job site to a place with fresh air, give oxygen when you have difficulty breathing, and then seek medical treatment.

Note Elements that cannot be conformal painted:

High power with heat dissipation surface or heat sink element, power resistor, power diode, cement resistor.

DIP switches, adjustable resistors, buzzers, battery holders, fuse sockets (tubes), IC sockets, tactile switches.

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

Plug-in or stick-type light-emitting diodes, digital tubes.

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

The screw holes of the PCBA board cannot be coated with conformal paint. The quality requirements are to strictly control the state of the PCB board after painting to ensure that the surface is flawless and the protection is in place.