In addition, it should be noted that sometimes the imposition base will not overlap with the printed circuit board graphics. Usually, the imposition base is cut along the edge of the imposition, and then single-piece alignment is performed, and the entire printed board is aligned and exposed. The above problems are the ones that should be paid attention to before the formal exposure of selenium solder mask.
Then, operate solar resistance soldering, and check whether the printed board is sucked and covered by the vacuum box before exposure. The pressure of the vacuum suction cover should be sufficient and no air is present. If the air is exposed, the ultraviolet light will be irradiated into the pattern along the side of the board, causing the shading part to be exposed, and the development will not be off. Sometimes, single-sided exposure is encountered. In this case, use a black cloth to separate the side with no patterns on one side from the ultraviolet light emitted by the exposure lamp. If the black cloth is not used, the ultraviolet light will pass through the side without patterns and be transmitted into the pad to make the hole in the pad hole. The solder resist cannot be developed after exposure.
When exposing printed boards with inconsistent patterns on both sides, first screen-print one side of the solder mask, then perform single-sided exposure, and after development, screen-print the other side of the solder mask. Because if both sides are screen-printed and exposed at the same time, one side has more complex patterns and needs more shading parts, while the other side needs less shading, so that the ultraviolet light is transmitted through one side to the other side, and the more shading side passes through the ultraviolet light. Irradiation, the image will not drop during development, which will cause rework or scrap.
During the exposure process, it is also encountered that the printed board after screen printing is not dried during curing. In this case, the solder resist will stick to the photographic plate during alignment, and the printed board will also need to be reworked, so if it is found that it does not dry, especially if most of the printed boards are not dried, they must be re-dried in the oven. These situations are easy to appear in the process of exposure, so it is necessary to check carefully, find out in time, and solve it in time.
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