PCB Tech - What are the problem of screen printing FPC demand research?

Analyze the key points of the screen printing technology of the upper double-sided flexible circuit board

Before screen printing, choose the raw materials to be used, and pre-baking the materials in advance, so that there will be no shrinkage and deformation problems in the screen printing, otherwise there will be many problems in the subsequent processing links, which will directly affect the screen printing. quality. In order to meet the design requirements, some of the double-sided flexible circuit boards require high dimensional accuracy, so they may be numbered A, which is distinguished by fraud and basic circuit B. Usually, carbon ink material is used to screen-print the A-side circuit. In the screen printing operation, the thickness of the ink must be controlled. After the ink thickness reaches the design requirements, the resistance requirements of all the circuits can be reached to ensure normal operation in the future. use.

Analyze the main points of concern when punching and filling carbon holes

Incorporating the summary of previous work experience, the diameter of the carbon filling hole is usually at the boundary of 0.8 ~ 1.0mm. In the process of filling the carbon hole, the size of the hole must be appropriate. If the carbon filling hole is too large, it is in the process of screen printing of the basic circuit.

If too much carbon ink penetrates through the carbon filling hole, the remaining ink will flow through the carbon filling hole. This kind of ink is not easy to finish. If it cannot be completely eliminated, it will remain on the screen printing table for a long time, which will not only affect the overall The aesthetics also easily cause short circuit problems in the circuit.

In addition, the width of the circuit is limited, so the size of the carbon hole cannot exceed this width boundary. If the diameter of the carbon filling hole is too small, there will be certain problems. There will be greater trouble in the future manufacturing of stamping dies, and PET is usually used. As a raw material, the blanking is not easy and scattered after the carbon filling hole is punched, and manual peeling can only be used. Otherwise, the carbon filling hole will be covered in the next process, which is not conducive to the effective flow of ink, and directly causes the upper layer and the base layer. There is an obstacle to continuity.

On the other hand, when the configured carbon filling hole is too small, the amount of ink penetrating is small, which makes the upper and lower layers of the circuit difficult to conduct. In view of this situation, the upper circuit surface must be studied when the carbon filling hole is stamped., Requires it to always face upwards, the key goal is to make the jagged rise, flashing, etc. face the side that is not screen-printed, which is conducive to the manipulation of the next process.

In order to increase the probability of the two layers of lines being turned on, it is better to add a carbon filling hole at the same point. The detailed interval of the configuration should be combined with the decision of the essential width, and the difference should not be too large or too small. Usually the carbon filling holes are relatively small, and the spacing between each other is relatively close. It is very troublesome to manufacture stamping dies. Usually, the craftsman will make two sets of dies. During the stamping process, it is better to punch one small hole at a time, that is, fill half of the carbon. The hole is completed in two times to achieve an excellent effect.

Analyze the concerns of screen printing grassroots circuits

In the process of screen printing double-sided FPC, the positioning hole should be used as a reference, and the base layer circuit should be printed on the side that has not been screen-printed. The upper layer also covers up a layer of ink. After the screen printing is completed, it has strong fluidity due to the effect of gravity, so that the carbon ink is very easy to fill the carbon holes, and the control is finally well connected to the upper line, so A side It is well connected with the B side, but if the drape faces the A side, the ink will flow to the A side line through the carbon filling hole when screen printing on the B side. Under the blocking effect of the drape, it is better to set the drape height as h. In this way, the ink will not flow through the front, and it will not be well connected with A. It can be seen that in this situation, the A-layer circuit and the B-layer circuit are basically impossible to conduct. The fluidity of the screen printing conductive ink is also very important for the conduction of the carbon filling holes. The inks usually used are relatively dense and have poor intrinsic fluidity, resulting in a low probability that the upper and lower lines can be conducted. Therefore, the PCB factory is in When performing screen printing double-sided FPC, when the mechanical printing method is selected, and the vacuum suction device is used on the worktable, the fluidity of the conductive ink is improved. However, this countermeasure also has a flaw, that is, manipulation Afterwards, a large amount of ink will remain on the workbench. If the residual ink is not eliminated in time, the quality of the circuit will be reduced. When the manual printing method is selected, no vacuum suction device is installed on the workbench, and the network of the circuit is completed. After the printing operation, the circuit board should be placed for a period of time according to the essential conditions, and then placed in the drying oven for drying treatment, so that the ink can flow fully, so that the upper circuit and the base circuit will be well connected. However, the thickness of the ink must be effectively controlled during detailed screen printing, so that the line resistance value and design can be guaranteed.