PCB Tech - The role of PCB solder mask and flux

The role of PCB solder mask and flux
The Internet era has broken the traditional marketing model, and a large number of resources have been gathered together to the greatest extent through the Internet, which has also accelerated the development speed of FPC flexible circuit boards, and then as the development speed accelerates, environmental problems will continue to appear in PCB factories. In front of him. However, with the development of the Internet, environmental protection and environmental informatization have also been developed by leaps and bounds. Environmental information data centers and green electronic procurement are gradually being applied to the actual production and operation fields.
Solder mask is an important part of today's printed circuit board skills. The use of PCB solder mask has become so common, it is the most unusual to see that printed circuit boards without any solder resist coverage, except for some home-built circuits today, and even many prototype boards have solder masks, so their use is commercialized The production of printed circuit boards can be said to be common.
The purpose of printed circuit board soldering

As the name suggests, solder mask covers the area of printed circuit boards that are used to protect the circuit boards, printed circuit boards, from taking solder. In this way, only a solder-covered area is actually required, that is, where the component is the area to be soldered, the solder resist is free, and soldering can be performed, which provides many advantages. The most important thing is that only whereit has solder, and reach some areas by the solder, to avoid small short circuits caused by solder bridges can be significantly reduced. This is more and more important, because the very fine distance of many printed circuit boards today means that the small solder tracks in the soldering process can easily cause bridges and short circuits. Use solder mask to limit the areas where components will be welded where this problem is, and these areas can be designed accordingly.

In addition to its ability to prevent the solder from causing small bridges, the solder of the printed circuit board also serves as the substrate of the protective layer. Solder mask provides electrical insulation and protection against oxidation and corrosion. This over a period of time can improve the overall reliability of the printed circuit board, especially if it is exposed to harmful reagents.

What is PCB flux?

Printed circuit board solder resist is a permanent resin-based coating applied to the printed circuit board during the manufacturing process of the bare board. Solder mask is a permanent coating of resin formulations, usually green in color, which encapsulates and protects all the surface features of the printed circuit board, unless it is necessary to form a specific area of the solder joint.

Although green is the most widely used color as solder resist, almost any color can be used. Although it can be difficult to maintain accurate colors, it is possible to make them almost any color. However, from green, other popular colors are red and blue.

Use PCB solder mask

In order to make the solder mask of the printed circuit board meet the very accurate requirements of today's surface mounting skills, SMT printed circuit board, liquid photosensitive (LPI) solder resist is used. Previously, the soldering of printed circuit boards used the stencil printing used by the silk screen resisting application program.

The process of LPI is very different from the stencil printing used for solder mask. LPI separates coating and imaging operations to achieve the highest level of precision. The material used in the PCB solder mask by the bare printed circuit board manufacturer is in a liquid photopolymer method, and it uses epoxy or epoxy-acrylate resin technology and the entire board is coated with the material. The thickness of the material is usually about 30 microns to 20 microns or more copper on the bare PCB board. Once the resist material after the flux coating is dried, it is exposed to the desired image pattern, and then unfolded to obtain the desired solder resist pattern. Then developed a solder mask post-curing to ensure that it provides a tough and durable heat dissipation.