Common PCB Etching Types
It is a complex physical and chemical process to convert a bare board into a board with obvious graphics.
Presently, the typical process of printed circuit board processing is the pattern plating process. That is, first pre-plated an anti-etching lead-tin layer on the retained copper foil parts of the outer part of the board, and then chemically etching the remaining copper foil, and this process is known as PCB etching.
It should be noted that there are two layers of copper on the board when etching. Only one layer of copper has to be etched away and the rest will form the final required circuit. The character of this pattern plating type is that copper plating layer only exists below the anti-etching lead-tin layer.
Another method is plating copper on the entire board, areas except photosensitive film are just tin or anti-etching lead-tin layer. This process is called full plate copper plating process.
Compared with the pattern plating process, the biggest disadvantage of the full plate copper plating process is that the plate must be plated with copper twice and must be eroded away when etching. Therefore, when the conductor with very fine width will generate a series of problems. At the same time, side corrosion can seriously affect the uniformity of the lines.
Currently, tin or lead-tin is the most commonly used anti-corrosion layer, which is used in the etching process. Ammonia etchants are commonly used chemicals and do not react chemically with tin or lead-tin. They are mainly refer to ammonia chloride or ammonia etching solution.