There are three main coating methods of solder resist application:
A method of transparent printing whereby a fabric cloth (the screen) is placed on top of the board and solder resist applied to the screen is printed onto the board by applying pressure using a rubber board known as a "squeegee".
A method whereby solder resist that has been adjusted to a viscosity suitable for coating is atomized using a spray gun and sprayed onto the board to produce a membrane. Various methods exist, including airless spraying, air spraying, and rotational bell spraying.
A method in which low-viscosity solder resist is dropped in a curtain and boards are passed through it, covering the entire surface of the board in solder resist.
There are several types of solder resist, but currently the most commonly used types are, photoimageable (PI) solder resist and particularly alkaline developable solder resist, which was first developed by Taiyo Group. When using photoimageable solder resist, the solder resist pattern is created by washing away unnecessary parts using developer after solder resist has been applied to the entire surface of the board and exposed to light under the process described below (photolithography).
Copper circuit pattern formed.
Solder resist is applied to the entire surface.
Heated at 80°C for 20 to 30 minutes and dried to a tack-free finish.
・Exposed to UV light through negative film.
・Areas that have been exposed to UV light are cured.
・Uncured areas are washed away using developer.(rare alkaline aqueous solution)
・Heated at 150°C for 50 to 60 minutes and cured.
・Solder resist pattern formation completed.