The PCB manufacturing process can be complicated or simple, depending how much "finish" must be present in the final process.
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More on surface finishes
An Expert’s Guide to PCB Surface Finishes | Bay Area Circuits
Applying the surface finish is one of the last steps of manufacturing a printed circuit board. The surface finish on a PCB is typically applied after the soldermask process and is designed to prevent oxidation of the remaining exposed copper, …
Peter Brissette
DIY Fabrication
DIY etching with 3D printer-drawn photomask
CNC etched PCBs