The complete PCB manufacturing process is series of steps, which takes Gerber data as input. Gerber data is set of files which includes various parts of double-side prototype pcbas different set of layers (this is not layers in PCB). Normally Gerber data is printed on films in 1:1 aspects ratio with impression on scale. For e.g., copper layer, solder mask, silkscreen, vias, etc are printed separately.
In general, further raw materials are selected, which is PCB surface. Normally it is FR-4 board laminated with copper layer. Then drilling is done on board. This is initial process of manufacturing. Drill position and size is determined Gerber file. It has particular file for the same. As purpose of vias is to conduct two layers, electrographic film plating is done on holes/vias. This electrography is very raw which is later thickening and smoothen during electrolysis process. Just to surprise, that a good CNC (Computer Numeric Control) machines rotate at 100000 rpm.
Then the entire PCB is coated and applied with photo-resist. Photo-resist is sensitive to light exposure and it may become soluble or insoluble depending upon its nature. Normally, a positive photo-resist is used, which becomes soluble after exposure to light. The film developed in first stage is taken into use here. After photo resist is applied, the film is placed on the surface and it is exposed to ultra-violet light under extreme pressure. The portion which is not exposed to light remains on the surface to form substrate. The electroplating is done for appropriate thickness to custom PCB boards layer and contacting vias with layers. It is further laminated with TIN to protect loss of conducting layer.
Then multiple chemical process starts. The exposed area not containing TIN layer is dipped into chemical to remove extra copper, photo resist, etc. This process is repeated till a neatly TIN covered surface is obtained. Later on TIN is dipped into chemical solution to get it removed and have a neatly developed copper lining.
Solder mask is applied as dry film or a dense liquor. This can be put as paste or dipped in casts and then excess is removed. Then it is sprayed for protect vice coating. Solder mask is important as it covers most of the copper area, especially tracks from oxidizing and providing insulation during assembly. Only pads to be soldered are kept exposed.
Then silkscreen is provided which has names, logos and other printable items. It is very similar to normal printing, but again done on scale as per details provided in Gerber data.
The prototype circuit boards are almost final and then it is required to coat the exposed copper with requisite. Mostly lead and TIN solder or Immersion silver is used for the purpose as it provided excellent surface for soldering. Based upon soldering precision and signal speed, immersion gold can be used as gold is excellent conductor.
This is mostly the case with single layer or two layers PCB. In case it is multi-layer PCB, then after tin is removed, layers of PCB is pressed under high temperature of 200 degree and glued. This gluing is hour long process.