Matters needing attention in PCB splicing

1. FPC flexible circuit board lines or single lines are developed to produce bubbles

    The main reason: the bubbles between two or more lines are mainly due to the narrow spacing of the lines and the excessively high lines. The screen printing prevents the solder from being printed on the substrate, resulting in air or moisture between the solder resist and the substrate. In the curing and exposure, the gas is heated and expanded to cause the single line to be mainly caused by the line being too high. When the blade is in contact with the line, the line is too high, and the angle between the blade and the line is increased, so that the solder resist cannot be printed on the root of the line. There is a gas between the side of the root of the line and the solder resist layer, and bubbles are generated after being heated.

    Solution: When screen printing, visually check whether the screen printing material is completely printed on the substrate and the sidewall of the line, and strictly control the current during plating.


    2. FPC flexible circuit board hole has solder mask and graphics with pinhole

    The main reason: FPC flexible circuit board did not print paper in time when screen printing, causing excessive residual ink in the screen, printing residual ink into the hole under the pressure of the doctor blade, and the mesh number is too low, which will also cause holes. Solder resistance. The dirt on the photographic plate caused the FPC flexible circuit board to see no light during the exposure process, resulting in pinholes in the pattern.

    Solution: Print the paper in time and select the high-mesh screen for plate making; often check the cleanliness of the photographic plate during the exposure process.

   3. There are signs of blackening on the copper foil lines under the solder mask of the FPC flexible circuit board.

    The main reason is that the water of the FPC flexible circuit board is not dried after the board is wiped off, and the surface of the printed board before the solder resist is splashed by liquid or by hand.

Solution: Check whether the copper foil on both sides of the printed board is oxidized during screen printing.


4. FPC flexible circuit board surface is dirty and uneven

    The main reason is that dirt on the surface is caused by flying debris such as flying hair in the air. The uneven surface is caused by not paying attention to printing paper in time during screen printing, and removing residual ink of the screen to cause surface unevenness.

    Solution: The clean room should fully guarantee the cleanliness of the operator, avoid unrelated personnel to walk through the clean room, regularly clean the clean room, and timely remove the residual ink from the screen when printing on the screen.


    5. FPC flexible circuit board has ghosting and cracking

    The main reason: ghosting is because the FPC flexible circuit board is not firmly positioned during screen printing and the residual ink on the screen is not removed in time to deposit on the printed board, causing regular ink spots along the entire FPC pad. The crack is Due to the insufficient exposure during the FPC exposure process, there are fine cracks on the board surface.

    Solution: Fix the strong and timely paper with the positioning pin to remove the residual ink on the screen; measure the exposure so that the integrated value of the exposure lamp energy, exposure time and other parameters reach the level of 9-11, within this range There will be no cracks.

   6. FPC flexible circuit board color inconsistency on both sides and flashing whitening problem

    The main reason: the number of knives on both sides of the screen is very different, and there is a mix of old and new inks. It is possible to use a new ink that is stirred, and the other side is used to leave the old ink for a long time. The flashing is due to the excessive plating current and the thick plating, which causes the graphic lines to be too high. When the screen printing FPC flexible circuit board is screened, the scraping knife and the screen printing frame are screened at a certain angle, so the lines are too high on both sides of the line. Another reason is that the scraper knife has a gap, and the gap does not drop ink, causing a jump.

    Solution: Try to keep the number of screen printing tools consistent, avoid mixing of new and old inks; mainly control the plating current and check whether the scraper knife has a gap.