At present, the printed circuit board (PCB) processing of typical process using "pattern plating method". On the copper part of the outer layer of the need to retain the Board first, is the graphical portion of the circuit on a layer of lead corrosion resistance of tin plating layers, and then the remaining copper corrosion by chemical way, called etching. To note is that when Board is covered with two layers of copper. outer layer etching process is just a layer of copper in all must be etched away, the rest of the circuit will form the final need.
In the outer circuit of the printed circuit board processing process, there is another method, is to use photographic film to replace metal plating resist. This method is very similar to the inner layer etching process, you can see an inner layer etching in the fabrication process. At present, the corrosion resistance of Tin or lead-Tin is the most common, used in ammonia Etchant for etching process. ammoniacal etching agent is a chemical commonly used in liquid, without any chemical reaction with Tin or lead Tin. Ammoniacal etching agents mainly refer to the ammonia/ammonium chloride Etchant. In addition, in the market you can buy ammonia/ammonium sulphate etching liquid.
The sulfate-based etching liquid after use, of which copper can be separated by electrolysis method, it can be reused. Due to its corrosion rate is low, in General is rare in practice, but is expected to be used in chlorine-free etching. Sulfuric acid-hydrogen peroxide Etchant for testing corrosion of outer shape. Due to both economic and waste processing and many other reasons, this technology has not been widely used in the commercial sense is. further, sulfuric acid-hydrogen peroxide and cannot be used for lead and Tin resist etching, and this process is not a PCB layer in the main method, most people rarely of interest.