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PCBA conformal coating is a specially formulated coating used to protect circuit boards and their related equipment from the erosion of bad conditions, thus improving and extending their service life and ensuring the safety and reliability of use. The conformal coating has good resistance to high and low temperatures; it's curing into a transparent protective film, with superior insulation, moisture, leakage, shock, dust, corrosion, aging, corona resistance, and other properties. Circuit board three anti-paint from the chemical composition can be divided into acrylate, silicone, polyurethane, and conformal coating. Generally, brush, spray, dip, and other processes, coating drying, and curing, will form a protective film on the circuit board to play a moisture-proof, anti-salt spray, and anti-mold protection.
In practical applications, such as chemical, vibration, high dust, salt spray, humidity, and high-temperature environments, the circuit board may produce corrosion, softening, deformation, mold, and other problems, resulting in circuit board circuit failure. Moisture is the most prevalent and destructive major factor for PCB circuit boards. Excessive moisture will significantly reduce the insulation resistance between the conductor, accelerate high-speed decomposition, reduce the Q value, and reduce corrosion of the conductor.
The conformal coating process probably contains dross removal, cleaning, solder joints paste protection, solvent dilution, dip paint, drying, go to the protection process, the process is cumbersome, and relatively long hours, the entire process is completed more than 12 hours. Circuit board special nano waterproof coating is a colorless and transparent, non-toxic, non-combustible, non-combustible moisture-proof and salt spray corrosion of liquid nanomaterials, generally used in the form of brushing, spraying, soaking, and other processes. It is characterized by shorter film-forming time, surface drying and full drying time are significantly faster than ordinary conformal coating; the thickness of the film layer is thinner than the conformal coating after coating the PCB surface looks cleaner and neater; because the film layer is only a few microns, so the heat dissipation ability is stronger, and the heat evaporation is faster. But at present, the cost of nano waterproof coating is relatively high, mainly used for the current smart wear, portable smart terminals, and other electronic products PCB waterproof moisture.
PCB needs to be cleaned before using the conformal coating, and the processing methods are as follows:
(1) The PCB board is cleaned with washboard water, and alcohol cannot be used.
(2) PCB board completely cured before brushing conformal coating, cleaned board can be put into the oven to bake dry.
(3) If it is spraying conformal coating, shake the bottle before spraying, so that the paint inside can be uniform, and then sprayed against the board.
(4) If the paint is brushed on, mix the paint in the bucket well before brushing.
(5) All conformal coating curing time at room temperature is a few minutes to ten minutes, and fully cured are 24 hours. Can be heated to sixty degrees for half an hour to fully cure.
PCBA conformal coating operation method:
(1) Brush coating - commonly used, can produce an excellent coating effect on smooth surfaces.
(2) Spraying - the use of spray can type products can be easily applied to maintenance and small-scale production use, the spray gun is suitable for large-scale production, but the two spraying methods for the operation of the accuracy of the requirements of the higher, and may produce shadows (the lower part of the component is not coated with the conformal coating place).
(3) Automatic dipping - Dipping ensures complete coating without wasting material due to overspray.
(4) Selective coating - accurate coating without wasting material, suitable for high volume coating, but the requirements for coating equipment are higher.
Conventional non-coatable devices: paint high-power heat sinks, heat sinks, power resistors, high-power diodes, cement resistors, pull-code switches, potentiometers (adjustable resistors), buzzers, battery holders, fuse holders, IC holders, flick switches, relays, and other types of sockets, rows of pins, terminals, and DB9, plug-type or chip-type light-emitting diodes (non-indicating role), digital tubes, grounding screw holes.
Some standards of PCBA conformal coating:
(1) Spraying timing: conformal coating spraying must be tested, inspected, and thoroughly cleaned before PCBA assembly.
(2) Spraying coverage: when spraying paint, be careful not to spray to the part that does not need to spray paint. Conformal coating layer should be transparent, and uniform coverage of PCB boards and components, uniform color and consistency.
(3) Process steps: process steps for spraying A surface - surface drying - spraying B surface - room temperature curing.
(4) Coating thickness: spraying thickness is 0.1mm-0.3mm.
(5) Environmental conditions: All coating operations should be carried out at a temperature of not less than 16℃ and a relative humidity of less than 75%.
(6) Cleaning and baking: dust, moisture, and rosin must be removed from the surface of the PCBA board to be coated with conformal coating before spraying so that the conformal coating can adhere well to the surface of the circuit board. Baking conditions: 60 ℃, 30-40 minutes, in the oven after taking out while hot spraying better.
(7) Spraying area: the spraying area should be larger than the area occupied by the device to ensure full coverage of components and pads.
(8) Spraying thickness: the spraying should be smooth and even, there should be no bare parts, and the thickness of the coating should be between 0.1 mm and 0.3 mm.
(9) curing mode: after spraying the plug-in components more than one side upward horizontally place them in the air-drying rack on the table dry curing (baking methods can make the coating accelerate the curing).
(10) Avoid spraying area: when coating conformal coating on the PCB, all connecting plug-in devices, sockets, switches, heat sinks (tablets), and heat dissipation areas are not allowed to spray conformal coating.
(11) Multi-layer spraying: If a thicker coating is desired, it can be obtained by applying two thinner layers (it is required that the first layer must be completely dried before the second layer is allowed to be applied).