Solutions to Common Quality Problems with Flex PCB(Part 1)

1. Small bubbles

There are small air bubbles between the wire frames of the FPC printed circuit board or the side of a wire frame after development. The key reason: the small bubble between two or more branch wire frames is because the wire frame spacing is too narrow and the wire frame is too high. During screen printing, the solder mask material cannot be printed on the plate, resulting in gas or gas between the solder mask material and the plate. Moisture exists. The key to the shrinkage of a wire frame when the vapor is heated during drying and exposure is caused by the wire frame being too high. When the scraper touches the wire frame, the wire frame is too high, and the scraper and the wire frame are too high. The viewing angle between the wire frames becomes larger, so that the solder resist material cannot be printed on the root of the wire frame, so that vapor exists between the side of the root of the wire frame and the solder mask layer, which will cause small bubbles when heated.

The solution is: During screen printing, visually check whether the screen printing material is completely printed on the outer wall of the board and wire frame, and strictly control the amount of current during the electroplating process.

2. Solder mask in the hole

The reason is that the paper is not printed immediately during the screen printing, which causes too much residual printing ink to be deposited on the screen. The residual printing ink is printed into the hole under the working pressure of the squeegee. The solution is to print the paper immediately. There are also metal screens. If the screen mesh is too low, it will also lead to solder resistance in the holes. Use a high mesh metal screen to make the board. The viscosity of the printing material is too low. Use a high-viscosity printing material. The screen printing angle of the squeegee will increase the squeegee appropriately. From the perspective of screen printing, the scraper wound becomes round and sharpens scraper wound.

3. Skimprinting

The key is that the electroplating process current is too large and the coating is thick, resulting in too high pattern wireframes. When screen printing FPC printed circuit boards, because the squeegee and the screen printing frame form a certain angle of view, the two sides of the wireframe are If the wireframe is too high, the ink cannot be removed: it leads to skip printing. Another reason is that the squeegee has a gap, and the ink cannot be removed at the gap, which leads to skipping printing. The key to the processing method is to manipulate the electroplating process current and check the squeegee There is no gap.

4. Air oxidation

The copper foil wire frame under the solder mask of the FPC cable printed circuit board is a sign of blackening. The cause is that the water has not dried after the board is wiped, and the surface of the printed circuit board is splashed by liquid before the solder mask is printed or hand-molded However, the processing method is to visually inspect the double-sided copper foil of the printed circuit board for air oxidation during screen printing.

5. The pattern has a pinhole

The reason is that there is waste on the photographing base plate, so that part of the printed circuit board that should be exposed to light is not visible during the whole process of exposure, resulting in pinholes in the pattern. The solution is to often check the cleanliness of the photographing base plate during the whole process of exposure. degree.