The typical process of PCB processing is using "Pattern plating Method". First of all, to retain the needed copper part of the outer layers, that is, to pre-plate a layer of tin plating on the part of circuit, then etching the rest of the copper foil in a chemical way is called etching.
Outer Layer: developing → two copper tinned → peeling → etching → stripping tin
Inner Layer: developing → etching → peeling
There are two layers copper on the PCBA board, only one layer of copper must be etched off in the outer etching process, and the rest will form the final circuit.
There is another method in the process of printed circuit board outer layer circuit, which is to use photosensitive film instead of metal coating to resist corrosion.
At present, tin or lead tin is the most commonly used corrosion layer, used in the ammonia etchant of the etching process. Ammonia Etchant is a commonly used chemical liquid, and tin or lead tin doesn’t occurs any chemical reaction. Ammonia Etchant mainly refers to ammonia / ammonium chloride etching solution. In addition, ammonia / ammonium sulfate etching liquid can also be bought in the market.
The line width of inner layer is generally larger, so the Ring is enough; The line of outer layer is generally more dense and space is not enough, so this time it is necessary to find ways to achieve the purpose of making line in the small space.