PCB reduction process

Historically, the reduction method, or etching process, was developed later, but today it is most widely used. The substrate must contain a metal layer, and when the unwanted parts are removed all that is left is the conductor pattern. By printing or photographing all exposed copper is selectively coated with a mask or corrosion inhibitor to protect the desired conductive pattern from damage, and then these coated laminates or copper sheets are placed into etching equipment which sprites heated etching agents onto the surface of the plate. The etching agent chemically transforms the exposed copper into a soluble compound until all the exposed areas are dissolved and there is no copper left. A film remover is then used to chemically remove the film, removing the corrosion inhibitor and leaving only the pattern of copper. The cross-section of the copper conductor is somewhat trapezoidal, because even though the vertical etching rate has been maximized in the optimized spray etching design, the etching still occurs both downward and sideways. The resulting copper conductor has a side wall tilt that is not ideal, but can be used. There are also some other conductor graphic fabrication processes that can produce vertical sidewalls.

The method of reduction is to selectively remove part of copper foil on the surface of copper-clad laminate to obtain conductive pattern. Subtracting is the main method for the manufacture of printed circuit nowadays. Its main advantages are mature, stable and reliable process.

The reduction method is mainly divided into the following four categories:

Screen printing: (1) good upfront design circuit diagrams are made into silk screen mask, silk screen don’t need the circuit on part will be covered by wax or waterproof materials, and then put the silk mask in the above blank PCB, on the screen will not be etched on besmear again protectant, put circuit boards in the etching liquid, are not part of the protective cover will be corrosion, finally the protective agent.

(2) optical printing production: good upfront design circuit diagram on the pervious to light film mask (the simplest approach is to use the printer printed slides), to be part of the opaque color printing, then coated with light-sensitive pigment on blank PCB, will prepare a good film on the plate into the exposure exposure machine, remove the film after the circuit board with developer of graphical display, finally carries on the circuit etch.

(3) Carving production: the parts not needed on the blank line can be directly removed by using spear bed or laser engraving machine.

(4) Heat transfer printing: The circuit graphics are printed on the heat transfer paper by the laser printer. The circuit graphics of the transfer paper are transferred to the copper clad plate by the heat transfer printing machine, and then the circuit is etched.