The basic requirement for the etching quality of circuit board processing is to be able to completely remove all copper layers except for the corrosion-resistant layer, that's all. Strictly speaking, in order to accurately define, etching quality must include the consistency of wire line width and the degree of lateral etching. Due to the inherent characteristics of the current corrosive solution, it not only etches downwards but also in all directions, so side corrosion is almost inevitable.

Side etching is a frequently discussed issue in etching parameters, defined as the ratio of side etching width to etching depth, known as the etching factor. In the printed circuit industry, its range of variation is very broad, from 1:1 to 1:5. Obviously, a small lateral etching degree or low etching factor is the most satisfactory.

The structure of etching equipment and the different compositions of etching solution will have an impact on the etching factor or side etching degree, or in optimistic terms, it can be controlled. The use of certain additives can reduce the degree of lateral corrosion. The chemical composition of these additives is generally a trade secret, and their respective developers do not disclose it to the outside world. As for the structural issues of etching equipment, the following chapters will specifically discuss them.

In many ways, the quality of etching already existed before the printed circuit board entered the etching machine. Because there are very close internal connections between various processes or techniques in printed circuit processing, there is no process that is not affected by other processes and does not affect other processes. Many issues identified as etching quality problems actually exist in the process of film removal or even earlier. For the etching process of outer layer graphics, due to the prominent "inverted stream" phenomenon it reflects compared to most processes, many problems are ultimately reflected on it. At the same time, this is also due to the fact that etching is the last step in a long series of processes starting from self coating and photosensitive, after which the outer layer pattern is successfully transferred. The more links there are, the greater the likelihood of problems occurring. This can be seen as a very special aspect of the production process of printed circuits.