Three-proof paint process

1. Definition Conformal coating is a coating with a special formula, which is used to protect circuit boards and related equipment from environmental erosion, and has good high and low temperature resistance. The conformal coating is applied to the surface of the circuit board, and after curing, it will form a transparent three-proof protective film (the three-proof is moisture-proof, anti-salt spray, and mildew-proof).

2. The main application of conformal coating The PCB circuit board that has used conformal coating has the "three proof" properties of anti-fog, moisture-proof and mildew-proof, and also has the properties of cold and thermal shock resistance, aging resistance, radiation resistance, salt spray resistance, ozone corrosion resistance, vibration resistance, good flexibility and strong adhesion, so it is widely used. Typical application scenarios include the following:

<!--[if !supportLists]-->1.      <!--[endif]-->Residential & Commercial Conformal coatings (generic coatings) provide protection for electronic circuits in household appliances against the following:

<!--[if !supportLists]-->·        <!--[endif]-->water and detergents (washing machines, dishwashers, bathroom products, outdoor electronic LED screens);

<!--[if !supportLists]-->·        <!--[endif]-->Adverse external environment (display screen, anti-theft, fire alarm device, etc.);

<!--[if !supportLists]-->·        <!--[endif]-->chemical environments (air conditioners, dryers);

<!--[if !supportLists]-->·        <!--[endif]-->Harmful substances in offices and homes (computers, induction cookers);

<!--[if !supportLists]-->·        <!--[endif]-->All other circuit boards that require three-proof protection.

<!--[if !supportLists]-->2.      <!--[endif]-->Automotive Industry The automotive industry requires conformal coatings to protect circuits from hazards such as gasoline evaporatives, salt spray/brake fluids, etc. With the rapid growth of the use of electronic systems in automobiles, the use of conformal coatings has become a fundamental requirement to ensure the long-term reliability of automotive electronics.

<!--[if !supportLists]-->3.      <!--[endif]-->Aerospace Due to the special use environment, aviation and aerospace environment have strict requirements for electronic equipment, especially under the condition of rapid pressurization and decompression, it is still necessary to maintain good circuit performance, so the pressure stability of conformal coating has been widely used.

<!--[if !supportLists]-->4.      <!--[endif]-->Navigation Whether it is fresh water or salty seawater, it will cause harm to the electrical wiring of ship equipment, and the use of conformal coating can maximize the protection of equipment on the water surface and even submerged under water.

<!--[if !supportLists]-->5.      <!--[endif]-->Medical Conformal coating protects electronic equipment from external chemicals and special use environments, ensuring its continuous and stable operation.

<!--[if !supportLists]-->6.      <!--[endif]-->Outdoor electronics, etc

3. Conformal coating process specifications and requirements "Painting requirements"

<!--[if !supportLists]-->·   <!--[endif]-->喷漆厚度:漆膜厚度控制在0.05mm - 0.15mm,干膜厚度为25um - 40um。

<!--[if !supportLists]-->·   <!--[endif]-->Secondary coating: In order to ensure the thickness of products with high protection requirements, secondary coating can be carried out after the paint film has cured (whether to carry out secondary coating according to the requirements).

<!--[if !supportLists]-->·   <!--[endif]-->Inspection and repair: Visually inspect the coated circuit board to meet quality requirements and fix the problem. For example, when the pins and other protected areas are stained with conformal paint, you can use tweezers to clip absorbent cotton balls or clean cotton balls dipped in board water to scrub them clean, and pay attention not to wipe off the normal paint film when scrubbing.

<!--[if !supportLists]-->·   <!--[endif]-->Component replacement: After the paint film is cured, if you need to replace the component, you can do it as follows:

<!--[if !supportLists]-->·   <!--[endif]-->Solder the components directly with electrochrome iron, and then use a cotton cloth dipped in board water to clean the material around the pad;

<!--[if !supportLists]-->·   <!--[endif]-->soldering of alternative components;

<!--[if !supportLists]-->·   <!--[endif]-->Use a brush dipped in conformal paint to brush the welded area and allow the paint film to cure.

"Coating Process"

<!--[if !supportLists]-->7.      <!--[endif]-->Get ready

<!--[if !supportLists]-->·        <!--[endif]-->preparation of products, glues and other necessary items;

<!--[if !supportLists]-->·        <!--[endif]-->Determine the site of local protection;

<!--[if !supportLists]-->·        <!--[endif]-->Identify key process details.

<!--[if !supportLists]-->8.      <!--[endif]-->cleaning

<!--[if !supportLists]-->·        <!--[endif]-->It should be cleaned in the shortest time after welding to prevent welding residues from being difficult to clean;

<!--[if !supportLists]-->·        <!--[endif]-->Determine whether the main contaminant is polar or non-polar in order to select the appropriate cleaning agent;

<!--[if !supportLists]-->·        <!--[endif]-->If alcohol cleaning agent is used, attention should be paid to safety matters: there must be good ventilation and process rules for drying after washing to prevent the explosion in the oven caused by the volatilization of the residual solvent;

<!--[if !supportLists]-->·        <!--[endif]-->When cleaning with water, rinse the flux with alkaline cleaning solution (emulsion), and then rinse with pure water to clean the cleaning solution to meet the cleaning standard.

<!--[if !supportLists]-->9.      <!--[endif]-->Masking protection (if no selective coating equipment is employed), i.e. masking

<!--[if !supportLists]-->·        <!--[endif]-->Paper tape that does not transfer from self-adhesive film should be chosen;

<!--[if !supportLists]-->·        <!--[endif]-->Anti-static paper tape should be used for IC protection;

<!--[if !supportLists]-->·        <!--[endif]-->Some devices are shielded and protected according to the requirements of the drawings.

<!--[if !supportLists]-->10.    <!--[endif]-->Dehumidification PCBA (components) that have been cleaned and shielded must be pre-baked and dehumidified before coating; Determine the temperature/time of pre-baking according to the temperature that the PCBA (component) can allow.

The allowable temperature of the PCBA (component) determines the temperature/time comparison table for pre-baking

<!--[if !supportLists]-->11.    <!--[endif]-->Coating The process method of coating depends on the PCBA protection requirements, the existing process equipment and the existing technical reserves, and usually has the following implementations: [manual brushing].

<!--[if !supportLists]-->·        <!--[endif]-->Hand painting. Brushing is the most widely applicable process, suitable for low-volume production, complex and dense PCBA structure, and products with strict requirements for shielding and protection. Because the coating can be controlled at will by brushing, the parts that are not allowed to be painted can be protected from pollution;

<!--[if !supportLists]-->·        <!--[endif]-->Brushing consumes the least amount of material and is suitable for two-component coatings with a higher price tag;

<!--[if !supportLists]-->·        <!--[endif]-->The brushing process has high requirements for the operator, and the drawings and the requirements for coating should be carefully studied before construction, and the name of the PCBA components should be recognized, and the parts that are not allowed to be coated should be labeled with eye-catching marks;

<!--[if !supportLists]-->·        <!--[endif]-->The operator is not allowed to touch the printed insert with his hands at any time to avoid contamination.

【Hand dipping】

<!--[if !supportLists]-->·   <!--[endif]-->Manual dip coating method. The dip coating process can obtain the best coating effect, and can apply a uniform and continuous coating to any part of the PCBA. The dip coating process is not suitable for PCBAs with adjustable capacitors, trim cores, potentiometers, cup-shaped cores, and some devices with poor sealing.

<!--[if !supportLists]-->·   <!--[endif]-->Key parameters of the dip coating process:

<!--[if !supportLists]-->·   <!--[endif]-->Adjust the appropriate viscosity;

<!--[if !supportLists]-->·   <!--[endif]-->Control the speed at which the PCBA is lifted to prevent bubbles, usually not more than 1 meter per second.

【Spraying】 Spraying is the most widely used and easily accepted process method, which is divided into the following two categories: (1) Manual spraying is suitable for the situation that the workpiece is more complex and difficult to rely on automation equipment for mass production, and it is also suitable for the situation that the product line has many varieties but small quantities, and can be sprayed to a more special position.

<!--[if !supportLists]-->·   <!--[endif]-->Manual spraying. Manual spraying should be noted: paint mist can contaminate some devices, such as PCB inserts, IC sockets, some sensitive contacts and some grounding parts, and these parts need to pay attention to the reliability of masking protection. In addition, the operator should not touch the printed plug with his hands at any time to prevent contamination of the plug contact surface.

(2) Automatic spraying usually refers to the use of selective coating equipment for automatic spraying, which is suitable for mass production, good consistency, high precision and low environmental pollution. With the upgrading of industry, the increase of labor costs and the strict requirements of environmental protection, automatic spraying and spraying equipment is gradually replacing other coating methods.

<!--[if !supportLists]-->·   <!--[endif]-->Automatic spraying method.

【Key points of the coating process】 According to the requirements of IPC-A-610E (electronic assembly testing standard), it is mainly manifested in the following aspects: [Area].

<!--[if !supportLists]-->·   <!--[endif]-->Areas that cannot be applied:

<!--[if !supportLists]-->·   <!--[endif]-->Areas that require electrical connections, such as gold pads, gold fingers, metal through-holes, test holes;

<!--[if !supportLists]-->·   <!--[endif]-->batteries and battery holders;

<!--[if !supportLists]-->·   <!--[endif]-->Connector;

<!--[if !supportLists]-->·   <!--[endif]-->fuses and housings;

<!--[if !supportLists]-->·   <!--[endif]-->heat dissipation device;

<!--[if !supportLists]-->·   <!--[endif]-->Jumper;

<!--[if !supportLists]-->·   <!--[endif]-->lenses for optical devices;

<!--[if !supportLists]-->·   <!--[endif]-->Potentiometer;

<!--[if !supportLists]-->·   <!--[endif]-->Sensor;

<!--[if !supportLists]-->·   <!--[endif]-->There is no sealed switch;

<!--[if !supportLists]-->·   <!--[endif]-->Other areas where the coating will affect performance or operation.

<!--[if !supportLists]-->·   <!--[endif]-->Areas that must be applied:

<!--[if !supportLists]-->·   <!--[endif]-->All solder joints, pins, component conductor parts.

<!--[if !supportLists]-->·   <!--[endif]-->Areas that can be painted or not painted

<!--[if !supportLists]-->·   <!--[endif]-->No device green oil coverage area.

【Thickness】 The thickness range of each type of coating material is standard.

【Thickness test method】

<!--[if !supportLists]-->12.    <!--[endif]-->Dry Film Thickness Measurement Tools:

<!--[if !supportLists]-->·        <!--[endif]-->千分尺(IPC - CC - 830B)；

<!--[if !supportLists]-->·        <!--[endif]-->Dry film thickness gauge, micrometer, dry film meter.

<!--[if !supportLists]-->13.    <!--[endif]-->Wet film thickness measurement: The thickness of the wet film can be obtained by the wet film thickness gauge, and then the thickness of the dry film can be calculated by the proportion of the solid content of the glue, and the thickness of the wet film can be obtained by the wet film thickness gauge, and then the dry film thickness can be calculated.

【Quality Requirements】

<!--[if !supportLists]-->·   <!--[endif]-->There can be no paint flow and dripping on the surface of the circuit board, and attention should be paid to the part that does not drip to the local isolation when the brush is painted;

<!--[if !supportLists]-->·   <!--[endif]-->The conformal coating layer should be smooth, bright and uniform, and protect the surface of the pad, SMD component or conductor;

<!--[if !supportLists]-->·   <!--[endif]-->The surface of the paint layer and the components can not have bubbles, pinholes, corrugation, shrinkage holes, dust and other defects and foreign objects, no chalking, no peeling, note: before the paint film is dry, do not touch the paint film at will;

<!--[if !supportLists]-->·   <!--[endif]-->Locally isolated components or areas should not be coated with conformal coating.

Fourth, the common problems and solutions in the use of conformal coating

<!--[if !supportLists]-->14.    <!--[endif]-->Bubble problem

<!--[if !supportLists]-->·        <!--[endif]-->Problem performance: After coating, bubbles appear on the surface of the conformal paint layer, which will affect the protective performance and appearance of the paint layer.

<!--[if !supportLists]-->·        <!--[endif]-->Causes:

<!--[if !supportLists]-->·        <!--[endif]-->The lifting speed of PCBA during dipping is too fast, and if the lifting speed exceeds 1 meter per second in the dipping process, bubbles are easy to occur;

<!--[if !supportLists]-->·        <!--[endif]-->The surface of the circuit board is not completely dried before coating, and if the dehumidification is not complete, the residual moisture will form bubbles after coating;

<!--[if !supportLists]-->·        <!--[endif]-->If the paint is stirred too vigorously, air will be brought in and bubbles will be formed.

<!--[if !supportLists]-->·        <!--[endif]-->Solution(s):

<!--[if !supportLists]-->·        <!--[endif]-->For the dip coating process, the speed of lifting the PCBA is strictly controlled to ensure that it does not exceed 1 meter per second;

<!--[if !supportLists]-->·        <!--[endif]-->Before coating, ensure the effectiveness of the dehumidification process, and carry out pre-baking and dehumidification according to the temperature and time allowed by PCBA;

<!--[if !supportLists]-->·        <!--[endif]-->Stir the paint gently, such as using a low-speed agitator, and let it sit for a period of time to allow air bubbles to escape.

<!--[if !supportLists]-->15.    <!--[endif]-->Insufficient adhesion problems

<!--[if !supportLists]-->·        <!--[endif]-->Problem performance: Conformal coating is easy to peel off from the surface of the circuit board and cannot play a good protective role.

<!--[if !supportLists]-->·        <!--[endif]-->Causes:

<!--[if !supportLists]-->·        <!--[endif]-->The surface of the circuit board is not cleaned thoroughly, and there are contaminants such as oil stains and flux residues, which affects the combination of conformal coating and circuit board;

<!--[if !supportLists]-->·        <!--[endif]-->The type of conformal coating selected does not match the material of the circuit board, and different circuit board materials may require different formulations of conformal coating to ensure good adhesion.

<!--[if !supportLists]-->·        <!--[endif]-->Solution(s):

<!--[if !supportLists]-->·        <!--[endif]-->To ensure the quality of the cleaning process, select the appropriate cleaning agent according to the polarity or non-polarity of the main contaminants, such as using a suitable emulsion for polar contaminants, and then rinse with pure water;

<!--[if !supportLists]-->·        <!--[endif]-->When choosing conformal coating, the adaptability test is carried out according to the material of the circuit board to select the appropriate product.

<!--[if !supportLists]-->16.    <!--[endif]-->Localized misapplication problems

<!--[if !supportLists]-->·        <!--[endif]-->Problem manifestation: Conformal coating is applied in areas that should not be coated (such as gold pads, gold fingers, etc.), resulting in circuit connection problems or component performance being affected.

<!--[if !supportLists]-->·        <!--[endif]-->Causes:

<!--[if !supportLists]-->·        <!--[endif]-->Operator error during manual brushing or spraying, failure to effectively shield and protect areas that should not be coated, or careless coating to these areas;

<!--[if !supportLists]-->·        <!--[endif]-->In the case of automatic spraying equipment, the equipment is misapplied due to the wrong program setting or the equipment malfunction.

<!--[if !supportLists]-->·        <!--[endif]-->Solution(s):

<!--[if !supportLists]-->·        <!--[endif]-->For manual operation, improve the operator's skills and sense of responsibility, carefully confirm the area that should not be coated before coating and make eye-catching marks, and operate carefully during construction;

<!--[if !supportLists]-->·        <!--[endif]-->For automatic spraying equipment, carefully check the equipment program settings before use, and regularly maintain the equipment to ensure the normal operation of the equipment.

Fifth, the future development trend of conformal coatings

<!--[if !supportLists]-->17.    <!--[endif]-->R&D of environmentally friendly conformal coatings

<!--[if !supportLists]-->·        <!--[endif]-->With the increasingly stringent environmental protection requirements, the use of traditional conformal coatings containing volatile organic compounds (VOCs) will gradually be restricted. The research and development of low-VOC or even VOC-free environmentally friendly conformal coating has become an inevitable trend, which must not only meet the existing protective performance requirements, such as moisture-proof, anti-salt spray, anti-mildew, etc., but also minimize the impact on the environment and human health during production and use.

<!--[if !supportLists]-->18.    <!--[endif]-->High-performance multifunctional conformal coating

<!--[if !supportLists]-->·        <!--[endif]-->In the future, conformal coatings will develop in the direction of high performance and multi-function. For example, in addition to existing protection, it may have better thermal conductivity to meet the increasing demand for heat dissipation in electronic devices, as well as self-healing capabilities that automatically repair minor damage to the paint layer to maintain the integrity of the protective properties.

<!--[if !supportLists]-->19.    <!--[endif]-->Intelligent coating process

<!--[if !supportLists]-->·        <!--[endif]-->In terms of coating process, intelligence will be the direction of development. Using artificial intelligence and automation technology, the coating equipment can automatically adjust the coating parameters according to the structure and coating requirements of the circuit board, such as coating thickness, coating area, etc., which can not only improve the accuracy and consistency of coating, but also reduce human operation errors and improve production efficiency.