In pcb manufacturing process silicone three-anti-paint application
In pcb manufacturing process ,PCBA’s three-anti-coating technology is receiving increasing attention due to the fact that PCBA, which is operated in harsh environments such as high humidity, high salt, dust and vibration, is susceptible to system failure due to salt spray, moisture and mold. Three anti-paint refers to the application of a uniform thickness of three anti-paint in the area where PCBA needs to be protected. It can effectively isolate the area and electronic equipment that PCBA needs to protect and its working environment, and fully protect PCBA from Damage, thereby improving the reliability of the PCBA and further improving the reliability of the electronic device.
1.Three- anti-coating technology and application technics
Before using the three-anti-paints, it is necessary to ensure that the surface of the PCBA is clean to ensure good adhesion in pcb manufacturing. The three-anti-coating processes include different technics such as spraying, brushing and dip coating. The coating technics is different, and the three anti-paint requirements are not the same. When using the spraying technics, the three anti-coating paints have the lowest viscosity requirements to meet the “spraying” capability requirements, while the dip coating requires the three anti-paints to have the highest viscosity.
The viscosity of the three-anti-paints is determined by the solid content of the three-anti-paints in pcb manufacturing process. The three anti-paint manufacturers generally have their own diluents to dilute the products with different concentrations to meet different coating technics requirements
2.The basic coating method of the three- anti-paint
Hand spray, dip coating and brushing method, although the operation is simple, no equipment investment is required, but the coating quality is difficult to be ensured, the thickness of the coating film is poor consistency, the three-anti-paint loss is large, the environment is polluted, It is easy to splash and pollute to adjacent sockets when plating, can not achieve selective spraying, requires manual adhesive tape to cover the protective device before coating, some components between the slit and the side of the component can not be sprayed. The existence problems has affected the quality of the products and needs to be solved urgently. The selective automatic coating machine is the perfect solution to the above problems. It can achieve precise spraying of PCBA. The spraying head can avoid the three-anti-paint not attach components and ensure the coating thickness is uniform in pcb manufacturing process.
3.Selective automatic coating equipment performance
To ensure high quality of the three-anti-coating, the selective automatic coating machine should meet the following technical parameters and performance requirements:
A.Online automatic flow operation to reduce manual turnover;
B. It has the functions of irregular continuous curve and three-axis linkage such as point/line/face/arc/circle;
C. Multiple different spraying heads can be hung at the same time. The equipment can be automatically switched according to different spraying requirements to meet different spraying area requirements in pcb manufacturingprocess;
D. CCD visual alignment system can be selected to eliminate PCBA or fixture positioning error and improve spraying accuracy;
E. Can accurately control the amount of three-anti-paint spray.
F. Three-anti-coating technics requirements
To achieve high-quality three-coating, the following technics requirements are required for three-anti-coating:
For components that cannot be stained with three-anti-paints, such as connectors, plug-in device, buttons, light-emitting diodes and gold fingers, when using brush coating, dip or manual spraying, it is necessary to add masking tape. Even with a fully automatic selective coater, if the coated area is too close to the non-stickable position (less than 5 mm), isolation prevention is required in pcb manufacturingprocess.
The surface of PCBA needs to be cleaned before coating to remove abnormal matter on the surface of PCBA. For products such as automotive, aerospace, marine and military, which require strict requirements, the coating can be applied after the PCBA is washed and dried, but for the low requirements general products, dry high pressure gas can be used to remove dirt such as dust on the surface of PCBA.
Before using the selective automatic coating machine for mass production, it is necessary to pay attention to the first piece of inspection work. It is confirmed that there are no problems such as leakage coating, less coating, multiple coating, and air bubbles. The device or the area where the coating is prohibited from being coated cannot be adhered, and the thickness of the coating is uniform, and baking can be performed in pcb manufacturingprocess.
The working environment humidity should be controlled below 65% RH when the three- anti-coating is applied. The PCB will absorb moisture as a composite material in pcb manufacturingprocess. If moisture absorption occurs, the three anti-paint will not fully protect. Therefore, after the assembly of the circuit board, the three-anti-coating technics should be carried out as soon as possible. If the PCBA is left for a long time and then sprayed with three-anti-paints, it is best to pre-bake before spraying. The baking temperature is 60 ° C and the time is 24 h.
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