PCB Etching Problems
The basic requirement for good PCB etching is to completely remove all the copper layers except the resist layer. Strict speaking, a good etching effect requires the consistency of the wire width and good side etching degree. Due to the inherent characteristics of the current corrosion solution, the etching effects to the down, the left and right direction, so the side etching is almost inevitable.
When consider the etch parameter, the side etching problem is often discussed, which is defined as the ratio of the side etching’s width to its depth, also called the etching factor. In PCB board industry, it varies widely from 1:1 to 1:5. Obviously, small side etching degree or low etching factor is the most satisfactory.
The structure of the etching apparatus and the etching solution of the different compositions have effects on the etching factor or the side etching degree. The usage of some additives can reduce side etching degrees. However, chemical compositions of these additives generally are business secrets, their developers won’t disclose them to the public.
In theory, the ideal state of graphics plating process during the etching stage is that total thickness of plated copper and tin or copper and lead-tin shouldn’t exceed the thickness of the plating-resist photosensitive film. However, the thickness of coating graphics fabricated by worldwide manufacturers is always much thicker than the photosensitive graphics in reality. In the process of electroplating copper and lead-tin, the lateral stacking problem arises as the coating exceeds the photosensitive film.