PCB Technical - PBT engineer talks about the three-proof coating of PCBA

The three-proof paint refers to coating a layer of uniform and common three-proof paint on the area where PCBA needs to be maintained. It can effectively block the area and electronic components that need to be maintained by PCBA, as well as its operating environment, and adequately maintain PCBA from Damage, thereby improving the reliability of PCBA, and further improving the reliability of electronic equipment. The PCBA of electronic equipment operating in harsh environments such as high humidity, high salt, dust, and vibration is susceptible to system failures caused by salt spray, moisture, and mold. Therefore, PCBA's three-proof coating technology is attracting increasing attention .

1. Three-proof coating technology and application process

Before applying the three-proof paint, we need to clean the PCBA to ensure a clean appearance to ensure that the three-proof paint adheres well. Three anti-coating processes include spraying, brushing and dip coating and other different process methods. The coating process is different, the three anti-paint viscosity requirements are also different. When selecting the spraying process,

the three-proof paint requires the lowest viscosity to meet the "spraying" ability requirements, while the dipping requires the highest viscosity of the three-proof paint. The viscosity of the three-proof paint is determined by the solid content of the three-proof paint. The manufacturers of the three-proof paint generally have their own thinners to dilute products with different concentrations and are used to different coating process requirements. The PCBA cleaning machine of Bo Yi Sheng adopts a fully pneumatic method and does not connect to the power source at all, so there is no risk of fire. At the same time, it uses environmentally friendly water-based solvents, which will not harm the environment or people's health. It is safe and environmentally friendly. of.

PBT engineer talks about PCBA's three-proof coating technology

Second, the basic coating method of three anti-paint

Usually hand spraying, dipping and brushing methods. Although the operation is simple and does not require any equipment investment, the coating quality is difficult to be guaranteed. There are poor coating film thickness commonality, large loss of three-proof paint, pollution to the environment, and coating. Sometimes it is easy to splash and contaminate adjacent sockets, selective spraying cannot be completed, the need to manually stick adhesive paper to cover the devices that need to be protected before coating, and some slits between the components and the side of the components cannot be sprayed. The existence of these problems has affected the quality of the products and is urgently needed to be dealt with. The selective active coating machine is the perfect solution to the above problems. It can complete the accurate spraying of PCBA, the spraying head can avoid the non-stick paint components, and the spraying thickness is uniform and common.

3. Selective active coating equipment performance

To ensure the high quality of the three-proof coating, the selective active coating machine should meet the following technical parameters and performance requirements:

1. On-line fully active flow operation, reducing manual turnover procedures;

2. It has functions such as point/line/surface/arc/circle continuous connection of irregular curves and three-axis linkage;

3. Multiple different spraying heads can be hung at the same time, and the equipment can be automatically switched according to different spraying requirements to meet the requirements of different spraying areas;

4. CCD vision centering system can be selected to eliminate PCBA or fixture positioning errors and improve spraying accuracy;

5. It can accurately control the spraying volume of the three-proof paint.

Four, three anti-coating process requirements

To complete high-quality three-proof coating, it is necessary to satisfy the following process requirements during the three-proof coating:

1. For components that cannot be stained with three-proof paint, such as connectors, connectors, buttons, light-emitting diodes, and gold fingers, when using brush coating, dipping or manual spraying, it is necessary to attach masking tape. Even if the fully active selective coating machine is used, if the coating area is too close (less than 5 mm) to the non-paintable position, barrier precautions must be taken.

2. Before coating, it is necessary to clean the surface of PCBA and remove foreign matter on the surface of PCBA. For products with strict requirements such as automobiles, aerospace, sailing and military industries, PCBA is required to be washed and dried before coating, but the requirements are not high. For general products, dry high-pressure air can be used to remove dirt such as dust on the surface of the PCBA.

3. Before selecting the selective active coating machine for mass production, it is necessary to pay attention to the first piece inspection operation. Make sure that there are no problems such as missing coating, less coating, more coating, and air bubbles. The devices or areas that are forbidden to be coated, such as connectors, must not have adhesive paint, and the thickness of the coating is uniform before baking.

4. The humidity of the working environment should be controlled below 65% RH during the three-proof coating. PCB as a composite material will absorb moisture. If it absorbs moisture, the three-proof paint will not have sufficient maintenance effect. Therefore, the three-proof coating process should be carried out as soon as possible after the circuit board is assembled. If the PCBA is left for a long time and then sprayed with the three-proof paint, it is best to pre-bake the PCBA before spraying. The baking temperature is 60 degree Celsius and the time is 24h.