Analysis and Discussion of Common Problems in Pre-Processing of PCB Silkscreen

Analysis and discussion of common problems in the pre-processing of PCB screen printing:
(1) Dotted oxidation on the copper surface

There are oxidation spots on the copper surface, which can cause the solder mask to fall off during hot air leveling. Generally, after the printed board is delivered for use, the lines with oxidation spots are easy to break. This kind of oxidation point can be seen when the board is connected. After the problem is found, the squeezing roller and the cold air drying section should be checked.

(2) A large area of ​​copper is darkened after being blocked by printing.

After printing is blocked, a large area of ​​copper becomes dark, and the ink on the board looks inconsistent in color, and it also affects the adhesion of the ink and the copper layer, so it should be reworked immediately. Before rework, check the temperature of the squeezing roller of the brushing machine and the hot air drying section to see if the squeezing effect is good and whether the displayed temperature of the drying section is consistent with the actual temperature.

(3) Some places are not brushed
There are two types of places that are not brushed: there are obvious brush marks on the left side of the same printed board, but not on the right side; there are brush marks on the middle part of the same printed board.

The first is caused by the non-parallelism between the brush rollers. This is mainly caused by placing the small board on the right side. Over time, the brush roller has changed from a cylindrical shape to a truncated cone shape, which appears when it encounters a large board. The second is caused by the uneven placement of the board by the operator. The brush roller should be checked frequently in normal times. The inspection method is: put a substrate directly under (upper) of the brush roller, without driving, turn on the brush roller, which will leave abrasion marks on the substrate. Under normal circumstances, the edge line of the wear scar is required to be two substantially parallel lines.

Equipment maintenance:

In order to reduce the increased production cost of pre-processing rework, the pre-processing equipment should be maintained on a regular basis. The maintenance of the equipment is not to wipe off the outer surface of the machine. The function of maintenance is to keep the machine in normal working condition.
Always check whether the brush roller is in the working state. It should not be refurbished with a sandboard of the same length as the brush roller. Usually, check whether the nozzle is blocked or not, so as not to affect the pretreatment effect. The maintenance of the squeezing roller is very important. When the squeezing roller works in a dry and hard state, the effect of pre-treatment is not achieved, and the service life of the squeezing roller is shortened. This is also to protect the squeezing roller from being half dry. The reason for the status.