The application of Conformal Coating in PCB
Conformal Coating is a method of coating on the circuit board to form a protective film. This layer of protective film is usually only 30 to 210 micron thickness, which can enhance the moisture -proof, pollution -proof, dustproof and chemical pollution capacity of electronic products, and also prevent the container and air conductor and the air conductor and the air corrosion. In addition, it can shield and eliminate certain electromagnetic interference and play an insulation role.
This coating also has an additional use, which is to improve the abrasion resistance and solvent resistance of components, and alleviate the stress caused by changes in high and low temperature. Therefore, Conformal Coating is often used in products that need to be exposed to harsh environments, such as multi -chemical gas, high pollution, multi -dust environment, high humidity, and extremely low or low temperature environment. In consumer electronics, it is often used to protect or inside some motor products or electronic component devices, such as motors, generators, transformers, and solenoid valve switches.
The products used on gas stations or aviation aircrafts need to meet the ATEX specifications. Coating Conformal Coating is one of its requirements. The purpose is to avoid short -circuit and sparks that may cause electronic products in special environments, causing fires or explosions, causing accidental losses.
The coating materials of Conformal Coating mainly have three transparent materials: Silicone, Acrylic, and Urethane. They also use EPOXY, but they are less used due to opaque. The solidification method can be curing or heating and curing at room temperature.
The following are the characteristics and precautions of the four types of Conformal Coating materials
- Silicone: After curing, it is usually transparent and elastic, which can effectively prevent shock-proof, and tolerate a large temperature change (-40 ° C ~ 200 ° C);
- Acrylic: transparent and hard after curing, low hygroscopic, short -curing time, abrasion resistance and good insulation;
- URETHANE: After curing, it is transparent and hard, with excellent abrasion resistance, good moisture -proof performance, stable performance in low temperature environment, but not high temperature;
- Epoxy: Strong and opaque, anti -humidity and prevention, good anti -chemical corrosion and abrasion resistance, and have good dielectric characteristics;
- When coating the Conformal Coating, you need to pay attention to avoid coating parts that require electrical contact or circuit connection, such as the contact film of the power socket and the connector, otherwise it will cause poor electrical. In addition, open parts such as beeur and speakers have an open hole, and the entry of the coating will affect the frequency of vibration and sound. LED should not be coated, otherwise the light will become darker or color changes.
The coating method of Conformal Coating mainly has the following
- Dipping: Suitable for large devices, the thickness of the coating is affected by temperature, time, drawing speed, vertical time, and wind knife;
- Spraying: Suitable for small and medium -sized devices, similar to spray paint, uniformity depends on the movement speed, spray position and pressure, etc. The bottom of the parts needs to be treated with additional treatment;
- Brush: Suitable for small devices, which are easy to be uniform because the skills are not familiar. Pay attention to the problem of brushing hair loss, and it is difficult to apply at the bottom of the part;
- Selective Coating: Despite time -consuming and consumable, selective coating required;
- CONFORMAL Coating tests are usually achieved by adding ultraviolet fluorescent agents. Most materials are transparent or lighter after spraying, and it is difficult to directly check the naked eye. Therefore, UV light (UV) inspection machine detect the spray effect and uniformity.
When selecting the Conformal Coating material, it is necessary to pay attention to its solidification conditions. Some need high temperature curing, and some only require room temperature. High temperature curing is usually high in hardness, and abrasion resistance; room temperature curing is elastic and soft.
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