The plated panel is now ready to be resist stripped, this is carried out by spraying a chemical at the resist, which swells the resist and then removes it from the copper surface. Track patterns which are isolated are difficult to strip, if poorly stripped, they will lead to short circuits. The best fix for this is to fill unused areas with circular dots, to even out the plating, and hence make the resist stripping easier.
The resist stripped panel is now ready for etching. An etching solution is then sprayed at the panel, this solution will attack the copper not covered by the tin resist. The amount of time the panel spends in the etch chamber dictates the amount of copper etched, i.e. etching 2 oz (70 micron copper) is half the speed of etching 1 oz (35 micron copper).
The etching of controlled impedance tracks is more critical, and a sample should be measured to ensure desired track width.
The panel is now etched and ready for tin stripping. The only function of the tin was to protect the copper tracks and plated holes. A chemical is now sprayed at the tin, which then chemically attacks the tin, but does not attack the copper. Leaving the tin stripped panel with bright shiny copper.
Tin Stripped ready to Solder
Once Tin Stripped, sectional view look as follows, copper tracks and copper holes