What is the purpose of PCB exposure in PCB manufacturing process
The process of solder mask exposure and development in PCB manufacturing is PCB with solder mask after screen printing. The solder pad on PCB board is covered with diazo film, so that it will not be exposed to UV during the exposure process, while the solder mask protective layer is more firmly attached to PCB board surface after UV irradiation, because the solder pad is not exposed to UV light, the solder pad can be exposed, so as to lead tin in hot air leveling.
The purpose of circuit board exposure is to produce optical polymerization reaction through ultraviolet irradiation and phenanthrene block, transparent place of film and dry film. That is to say, under ultraviolet irradiation, the photoinitiator absorbs light energy and decomposes into free radicals, which are then led to the polymerization and crosslinking reaction of photoinitiator. After reaction, the large molecular structure insoluble in dilute alkali solution is formed. Film is brown, UV light can't penetrate, film can't polymerize with its corresponding dry film. The exposure is generally carried out in the automatic double-sided exposure machine.
There are two kinds of exposure: line exposure and resistance welding exposure. The function is to solidify the irradiated local area by UV light, and then develop it to form circuit pattern or solder mask pattern.
The process of line exposure is to stick a photosensitive film on the copper clad plate first, and then put it together with the line graphic negative to expose with ultraviolet light. The photosensitive film irradiated by ultraviolet light will polymerize. The photosensitive film here can resist the scouring of Na2CO3 weak alkali solution during development, while the part not sensitive to light will be washed off during development. In this way, the circuit pattern on the negative film is successfully transferred to the copper clad plate;
The process of solder mask exposure is the same: apply photosensitive paint on the circuit board, and then cover the place to be welded during exposure to make the pad exposed after development.