PCB circuit board because of many processes, in the production time is also very particular, the inner and outer layer etching method is not the same, the more obvious difference is the inner layer of

the general line width line distance is larger, the outer layer of the line is more dense.

Inner layer: development → etching → stripping

Outer layer: development → tinning → stripping → etching → stripping

Because the outer line is very dense, the space is not enough, so at this time, you need to find a way to achieve the purpose of making the line in the insufficient space. The ability of alkali corrosion

can reach 1~2mil ring, but acid corrosion requires about 5mil, so it is necessary to use tin to protect the required line.

It should be noted that PCB boards should not be done in places where corrosion can be avoided, because the cost of corrosion is higher than acid corrosion. The etching factor is the manufacturing

capacity of a plant, which cannot be improved by the process. Acid-base etching has different etching abilities.