10 Common Problems of FPC Flexible Board Surface Defects

With the gradual development of electronic products, they turn to become short, small, light and thin, the advantages of FPC flexible board is are very obvious, the market demand is also increasing. Due to the mass production process of flexible board, the board defects often caused by improper operation. Here I compiled a list of 10 common problems, let’s have a look.

10 Common Problems of FPC Flexible Board Surface Defects

1、Bubble

FPC printed board between the lines or a single line side, there are bubbles after the developing. The main reason: two or more lines between the bubble is mainly due to the line spacing is too narrow and lines are too high, screen printing so that the solder resist can not be printed on the substrate, resulting in the presence of air or moisture between the solder resist and the substrate, in the curing and exposure of gas expansion caused by heat single lines is mainly due to the lines are too high.

In the squeegee and the line contact, the line is too high, the angle between the squeegee and the line increases, so that the solder resist material can not be printed to the root of the line, so that the side of the root of the line and the solder resist layer between the gas exists, the heat produces bubbles, the solution has: screen printing should be visually inspected when the screen printing material is completely printed to the substrate and the side wall of the line, plating when strictly control the current.

2、Welding in the hole

The cause is not timely printing paper in the screen printing, resulting in the accumulation of residual ink in the screen too much residual ink printed in the hole under the pressure of the squeegee, the solution is to print paper in a timely manner, and screen mesh is too low, will also cause the hole in the blocking welding, to use high mesh screen plate, the viscosity of the printing material is too low, replaced with a large viscosity of the printing material, the size of the squeegee screen printing angle, appropriate adjustment of the squeegee screen printing angle, squeegee knife mouth rounded, and Sharpen the squeegee blade.

3、Skip printing also known as blank

Mainly due to the plating current is too large, thick plating, resulting in graphic lines too high, in the screen printing FPC printing board, due to the squeegee knife and screen printing frame into a certain angle screen printing, so on both sides of the line due to the line is too high, it is not ink: resulting in jumping, another reason is the squeegee knife gap, the gap is not ink, resulting in jumping, the solution is mainly to control the plating current and check whether the squeegee knife has a gap.

4、Oxidation

FPC printed board solder resist layer under the copper foil lines on the signs of blackening, the cause of the wipe the board after the water is not dried, printed solder resist before the surface of the printed board was splashed with liquid or with hand mold, the solution is to screen printing visual inspection of the printed board on both sides of the copper foil whether there is oxidation.

5、Pinholes on graphic

The reason is that there is dirt on the photographic plate, so that the printing plate in the exposure process should see the light of the part did not see the light, resulting in pinholes in the graphics, the solution is to frequently check the cleanliness of the photographic plate in the exposure process.

6、Surface dirt

Because the FPC printing board screen printing room is a clean room, so, at the screen printing extraction should be an electrostatic line to play the role of adsorption of airborne debris such as flying hair, so in order to reduce the surface dirt, we must fully ensure the cleanliness of the clean room and the appropriate implementation of some specific measures: such as entering the clean room to fully ensure the cleanliness of the operator, to avoid irrelevant personnel walking through the clean room, regular cleaning of the clean room, etc.

7、Uneven surface

In the screen printing did not pay attention to the timely printing paper to clear the residual ink of the screen, resulting in an uneven surface, the solution is to print paper in time to clear the residual ink of the screen.

8、Heavy shadow

The entire FPC printing board pads next to the presence of regular ink dots, the reason for the appearance of the screen printing FPC printing board positioning is not secure and the residual ink on the screen did not remove in time to accumulate on the printing board, the solution is to use the positioning pin fixed firmly and timely printing paper to remove the residual ink on the screen.

9、The color is not consistent on both sides

The reason for this is that there may be a big difference in the number of knives between the two sides of the screen printing, there is also a mix of old and new ink, there may be a side with a good mix of new ink, while the other side is used to place the old ink for a long time, the solution is to try to avoid the appearance of the above two situations.

10. Crack

In the process of FPC exposure, the exposure is insufficient, resulting in small cracks on the board surface. The solution is to measure the exposure so that the comprehensive values of exposure lamp energy, exposure time and other parameters reach between 9-11 exposure stages, and there will be no cracks in this range.