PCB Technical - Moisture-proof, insulating, anti-corrosion paint, circuit board surface coating

Moisture-proof, insulating, anti-corrosion paint,circuit board surface coating

Conformal Coating is a method of coating on a printed circuit board and forming a protective film. This protective film is usually only a thin layer (about 30-210 μm), which can be used to strengthen the moisture-proof and waterproof of electronic products. The ability of pollution, dust, and chemical resistance can also prevent the solder joints and conductors from contacting the air and continue to corrode. It can shield and eliminate some electromagnetic interference, and it can also play a role in insulation. This coating has an additional purpose, that is, it can increase the wear resistance and solvent resistance of components, and it can also release the stress caused by high and low temperature changes.

Because it has these various advantages, it is often used in products that need to be exposed to extremely harsh environments, such as multiple chemical atmospheres, highly polluted and dusty environments, high humidity environments, and extremely high or low temperature environments. In consumer electronic products, it is often used to protect or insulate some electrical products or electronic components, such as motors, generators, transformers, electrical delay valve switches, etc.

The conformal coating materials are basically three transparent materials such as Silicone (silicone, silicone), Acrylic (acrylic), and Urethane (polyurethane), and some use Epoxy (epoxy resin), but it is an opaque material. So fewer people use it.

The curing method of conformal coating can use room temperature curing and heating curing.

The characteristics and precautions of these four conformal coating materials are summarized below:

After curing, the Silicone material usually appears transparent and elastic rubber state, which is more effective in shock resistance, and can also withstand severe stress changes (-40°C~200°C) caused by large high and low temperature changes.

Acrylic material usually presents a transparent and hard coating after curing, with low moisture absorption and faster curing time, good wear resistance and insulation.

Urethane material usually presents a transparent and hard coating after curing. It has excellent abrasion resistance and good moisture resistance. Its performance in low temperature environments is particularly stable, but it is less resistant to high temperatures.

Epoxy-based coating material is very strong, usually opaque, has good moisture and moisture resistance, and its anti-chemical corrosion and wear resistance performance is also very good, in addition, Epoxy also has good dielectric properties (dielectric properties) .

When applying conformal coating, pay attention to avoiding some contact or circuit connection parts during subsequent processing, such as power jack, connector, speaker (buzzer, speaker). Because the conformal coating is an insulating material, attaching to these components that require conductive contact will cause poor electrical properties.

Conformal coating coating methods can be roughly divided into 3+1 types:

Dipping: It is more economical for large-scale equipment, but the thickness after coating will be affected by the temperature, time, extraction speed, vertical flow time, whether to add an air knife... etc.

Spraying: It is 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.

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.

Selective coating (Selective Coating): Although coating has many benefits, it is often time-consuming and labor-intensive. You can also choose to coat the part that is needed.

Because most of the Conformal coatings are transparent and colorless after spraying, it is difficult to check the spraying effect with the naked eye. Therefore, most of the conforma coating materials will add a small amount of ultraviolet fluorescent agent, so as long as the installation of ultraviolet light can be used to check the spraying condition and uniformity.

When choosing a conformal coating material, you also need to pay attention to its heating conditions. Some need to be cured at a high temperature, and some can be cured at room temperature. Those cured at high temperature usually have higher hardness and can be abrasion resistant, while those cured at room temperature have the advantage of elasticity and are softer.

1. When using the spraying method, vacuum equipment is required, otherwise the sprayed substance will be dispersed into the air and affect the health of the human body.

2. During the spraying operation, you can use a jig to cover some places and parts that cannot be sprayed, so as to prevent the insulating material from being sprayed to some places that need to be conductive contact.

3. When making conformal coating, you can also use non-residual stickers to stick to some parts that cannot be sprayed.

4. The sprayed PCBA board can use ultraviolet light to check the spraying condition.