Conformal Coating in PCB
Anti-corrosion paint (Conformal Coating) is a kind of Coating on the circuit board to form a protective film, the method of the protective Coating is usually only a thin layer (about 30 ~ 210 (including m), it can be used to strengthen the electronic products of moisture-proof, antifouling and dust prevention, chemical pollution prevention ability, also can prevent the solder joint and the conductor is exposed to air and continue to corrosion problems, can rise to some electromagnetic interference shielding and eliminate, more can play the role of insulation
The conformal coating also has an additional purpose, which is to increase the wear resistance and solvent resistance of components, as well as to release the stress caused by high and low temperature changes.
Because of these advantages, conformal coating is often used in some products that need to be exposed to extremely harsh environments, such as multi-chemical environment, high pollution or dust environment, high humidity environment, very high or grade low temperature environment. In consumer electronics products are commonly used to protect or insulate certain motor products or electronic components such as motors, generators, transformers, solenoid valve switches... And so on.
Products used in gas stations or aircraft are required to comply with ATEX specifications, and conformal coating is one of the requirements, in order to avoid any electronic products in special circumstances may cause a short circuit, sparks and fire or explosion, resulting in loss of life accidents.
The coating materials for conformal coating include Silicone, Silicone, Acrylic, Urethane and other transparent materials. Some products also use Epoxy resin, but it is opaque, so it is seldom used.
Conformal coating curing method can be used room temperature curing and heating curing two.
The following are four types of conformal coating materials:
Silicone material usually presents a transparent and elastic rubber state after curing, which is more effective in preventing shock, and can also withstand the drastic stress change (-40°C~200°C) caused by large changes of high and low temperature.
Acrylic material is usually transparent and hard after curing. It has low moisture absorption, fast curing time, good abrasion resistance and insulation.
Urethane usually presents a transparent and hard coating after curing, which has excellent abrasion resistance and good moisture resistance. Its performance is especially stable at low temperature, but it is not resistant to high temperature.
Epoxy matrix coating material is very strong, usually is not transparent, has good moisture and moisture proof ability, its anti chemical corrosion and abrasion resistance performance is very good also, Epoxy also has good dielectric properties, dielectric properties).
Conformal coating precautions:
Anti-corrosion coating paint (conformal coating), need to pay attention to avoid coating to some subsequent processing needs to be done when the electrical contacts, or circuits connecting parts, such as Power socket (the Power jack), connectors (connector) of the contact piece, this is because the anti-corrosion paint (conformal coating) for insulation material, attached to these needs conductive components will cause poor electrical contact.
In addition, the buzzer, speaker is an open part with holes. Once the three-antifouling paint gets inside the part, it will affect the vibration frequency of the shrapnel and thus the sound.
Also, leds should not be coated, or the light from the leds may dim or change color.
Conformal coating can be divided into 3+1 coating methods:
Impregnation (dipping) : for large equipment is economic, but after the coating thickness are dipping temperature, time, velocity and the vertical flow of time, whether the wind knife... Etc.
Spraying: more economical for small and medium equipment. When the use of spray like spray paint, coating uniformity depends on the relative moving speed, spray position, spray pressure, whether there are higher parts and. In addition, the bottom of the part cannot be sprayed, which may require additional treatment.
Brush (for brushing) : for small equipment is more economic. Besmear when easy because of the skill of besmear skilled degree and cause besmear not even occurrence, also want to pay attention to the hair brush off the problem. Part bottom is also more difficult to coat.
Selective Coating (Selective Coating) : Coating, although a lot of benefits, but often time-consuming and time-consuming, you can also choose the required part of the location of Coating.
Conformal coating inspection
Because most Conformal coating is colorless and transparent after spraying, or a thin thin relatively light color, it is difficult to directly check the spraying effect with the naked eye. Therefore, most conformal coating materials will be added with trace amount of UV fluorescent agent, so as long as the installation of ultraviolet (UV) inspection machine can be used to check the coating status and uniformity.
When choosing conformal coating materials, it is also necessary to pay attention to its heating conditions. Some need to be cured at high temperature, while others can be cured at room temperature. High temperature curing usually higher hardness, can withstand wear, room temperature curing, elastic advantage of soft.
Equipment for vacuum extraction is needed when Spraying is applied; otherwise, Spraying material will be sprayed into the air and affect human health.