PCB Etching Types
The fabrication process of a printed circuit board is a complicated process of physical and chemical reactions that make a bare board into an advanced complex board. This article analyzes the last step during the fabrication process- PCB etching.
Presently, the graphic plating method is the typical PCB process way. That is to pre-plate a lead-tin resist layer on the retained copper part, and then chemically etch the rest of the copper foil, the whole process is known as PCB etching. It should be noted that there are two copper layers on the board. During the outer layer etching process, only one copper layer must be etched out, and the rest will be formed into the final desired circuit. This graphic plating type is characterized by the copper plating layer only put below the lead-tin resist layer.
Another method is to plate copper on the entire board, and area outside photosensitive film is only tin or lead tin resist layer. This process is called full board copper plating. Compared with the graphics plating, the biggest drawback of the full board copper plating is the board surface must be plated copper twice and they must be totally etched out later. So if the wire width is very fine, a series of problems will be produced. At the same time, side corrosion will seriously affect the line uniformity on the PCB board.
There is another way to fabricate PCB outer circuit, which is to use the photosensitive film instead of metal coating to do the etching resist layer. This method is very similar to the inner layer etching process.
At present, tin or lead-tin is the most commonly etching resist layer used in the etching process of ammonia etchant. Ammonia etchant is a commonly used chemical liquid which does not cause any chemical reaction with tin or lead-tin. Ammonia etchant mainly refers to ammonia/ ammonium chloride etchant.