hi my question is:why is a PCB exposed to UV light. what does the light do to the board?Cheers Av
PCBs start as a board covered by a solid sheet of copper and then a special photo-resist layer. The photo-resist is such that when developed it only remains if it has not been exposed to UV light, and it resists acid eating away the copper layer. In other words, the area exposed to UV light, when dipped in acid, is eaten away. Those areas not exposed to UV light 'resist' the acid and remain. By exposing to UV light through a drawn or printed pattern, you can precisely control what areas are or are not exposed. If you didn't expose to UV light before the acid dip, all the photo-resist would remain and you would end up with a solid copper sheet left on the board rather than traces and part pads.
PCBs start as a board covered by a solid sheet of copper and then a special photo-resist layer. The photo-resist is such that when developed it only remains if it has not been exposed to UV light, and it resists acid eating away the copper layer. In other words, the area exposed to UV light, when dipped in acid, is eaten away. Those areas not exposed to UV light 'resist' the acid and remain. By exposing to UV light through a drawn or printed pattern, you can precisely control what areas are or are not exposed. If you didn't expose to UV light before the acid dip, all the photo-resist would remain and you would end up with a solid copper sheet left on the board rather than traces and part pads.
