Custom PCB 2 Layer PCB Board
PCB procedure---- exposure.
First of all, before exposure start，check if the exposure frame of the polyester film and glass frame is clean, if not clean should be promptly wiped with anti-static cloth.
Then, open exposure machine power switch, then open the vacuum button to choose exposure, shake the shutter, before not formally exposure, should let exposure machine "empty exposure" five times, "the empty exposure" role is to make the machine to enter the working state of the saturated, the most important is to make the uv exposure lamp energy into the normal range.The energy of the exposure lamp may not be optimal if it is not "air-exposed".During the exposure will cause problems with the printed circuit board. after five times of "Air exposure", the exposure machine has entered the best working state, before using the photographic substrate alignment, need to check if the substrate is qualified. Check whether there are pinholes and exposed parts of the drug film surface on the base board, and whether they are consistent with the figure of the printed board, because this will check the photographic base plate to avoid reworking or scrapping the printed circuit board for some unnecessary reasons.
Soldering resistance usually adopts visual positioning, use silver salt base board, let the base board pad and printed board pad hole coincide, fixed with tape can be exposed.There are many problems in alignment. For example, because the substrate is related to temperature, humidity and other factors, if the temperature and humidity are not controlled properly, the photographic substrate may shrink or enlarge the deformation, so that in soldering resistance, the photographic substrate and the printed board pad is not completely consistent. When the base plate is reduced, see how much difference between the base plate pad and the PCB pad, if the difference is very small, can spray tin in hot air levelling, then there is no big problem can be selenium soldering.If the difference is very big, only turn round the board, try to make the base plate pad overlap.
Before alignment, we should also pay attention to whether the drug film surface of the base plate is inverted, should ensure that the drug film surface in alignment face down, if face up, so that the drug film surface is scratched, resulting in the exposure of the base plate, so that the printed board does not need to expose solder resistance,if serious will cause scrap of the printed board. In addition, also need pay attention to the bottom plate of the imposition will not coincide with the PCB graphics sometimes, usually the bottom plate of the imposition along the edge of the panel cut, and then single-match, exposure after the entire PCB on the good.The above problems should be paid attention to before the formal exposure of selenium resistance welding.
Then soldering, before exposure should check whether the printed board is vacuum box suction cover.The vacuum suction pressure should be sufficient without dew.If the air inside the graphics can make ultraviolet light along the side board, exposure causes shading, development not to drop, sometimes in case of single exposure, in this case, the single side did not have graphics is separated from the uv light exposure lamps with black cloth, if it's not black cloth, ultraviolet light through the side did not have graphics transmission to the welding plate make the resistance solder in welding plate hole after exposure, imaging.
When exposure the two sides inconsistent with the graphics, first screen printing one side resistance, and then to single exposure, after developing, resistanc on the other side of the screen printing. if the two sides screen printing exposure at the same time, there is a graphic complex welding pad, the part that needs shading much, and the other side needs shading part little, so that ultraviolet light through one side irradiation to the other side, after ultraviolet light irradiation for the side that has more shading, in the development of the shadow will not show off, will cause rework or scrap. During exposure, will meet the PCB after screen printing, in the case of curing without drying, in this case, the registration will make resistance solder stick to photoplate, moreover, PCB also want to rework, so for this statuion and most especially PCB without drying, will be back in on the oven drying. These situations are easy to appear in the process of exposure problems, so to check carefully, timely detection, timely solution.