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, affecting the adhesion of the ink and the copper layer. 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 ensure good squeezing effect and consistent displayed temperature with 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 non-parallelism between the brush rollers due to placing the small board on the right side, leading to brush roller deformation. The second is caused by uneven board placement by the operator. The brush roller should be checked frequently. Inspection method: place a substrate under the brush roller without driving, turn it on to leave abrasion marks. The wear scar edge line should be two substantially parallel lines.
Equipment maintenance:
To reduce production cost, pre-processing equipment should be regularly maintained. Maintenance is not just wiping the outer surface, but ensuring the machine works properly. Check the brush roller’s working condition and avoid refurbishing with a sandboard. Check for blocked nozzles to maintain pretreatment effect. Squeezing roller maintenance is crucial; ensure it works in a proper condition to achieve pre-treatment effect and prolong its service life. Protect the squeezing roller from half-dry status.
(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, affecting the adhesion of the ink and the copper layer. 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 ensure good squeezing effect and consistent displayed temperature with 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 non-parallelism between the brush rollers due to placing the small board on the right side, leading to brush roller deformation. The second is caused by uneven board placement by the operator. The brush roller should be checked frequently. Inspection method: place a substrate under the brush roller without driving, turn it on to leave abrasion marks. The wear scar edge line should be two substantially parallel lines.
Equipment maintenance:
To reduce production cost, pre-processing equipment should be regularly maintained. Maintenance is not just wiping the outer surface, but ensuring the machine works properly. Check the brush roller’s working condition and avoid refurbishing with a sandboard. Check for blocked nozzles to maintain pretreatment effect. Squeezing roller maintenance is crucial; ensure it works in a proper condition to achieve pre-treatment effect and prolong its service life. Protect the squeezing roller from half-dry status.
