PCB screen printing is an important link in the PCB manufacturing process. So, what are the common faults in the screen printing of PCB circuit boards?
1. Faults at the screen level
1. Blocking holes
The reasons for this kind of situation are: the printing material is too fast, the screen is dry and blocked, the printing speed is too fast, and the strength of the scraper is too high.
The solution is to use an organic solvent with slow volatiles to adjust the printing material, and use a soft cloth dampened with the organic solvent to gently clean the screen.
2. Screen ink leakage
The reasons for this type of failure are: there is dust and dirt on the surface of the pcb board or the printing material, which damages the screen during screen printing; in addition, during the printing plate making, the screen mask glue is not exposed enough, causing the screen mask to dry. Solid is not complete, resulting in ink leakage.
The solution is to stick it on the small round hole of the screen with tape or tape, or repair it with screen-making glue.
3. Screen damage and reduced precision
Even a screen of very good quality, after long-term application, its precision will gradually decrease or be damaged due to damage from scraping and printing pressure. The service life of the immediate legal screen is longer than that of the indirect legal screen. Generally speaking, the immediate legal screen is used for mass production.
4. Failure caused by excessive printing pressure
Too much pressure on the squeegee will not only cause a large amount of printing material to pass through, causing the squeegee to be bent and deformed, but will also cause a small amount of printing material to pass through, making it impossible to print a clear image on the screen, and will continue to cause damage to the squeegee and screen mask falling off, The wire mesh becomes longer and the image distorts.
Second, the failure caused by the PCB printing material level
1. Blocking holes
The printing material on the screen blocks a part of the mesh of the screen, resulting in less or no passing of the printing material in this part, resulting in poor packaging and printing graphics. The solution is to clean the screen carefully and carefully.
2. The back of the PCB board is dirty with printing material
Because the polyurethane coating of the printed material on the pcb board is not completely dry, the pcb boards are stacked together, causing the printing material to stick to the back of the pcb board and cause contamination.
3. Poor adhesion
The pre-treatment of the pcb board is very harmful to the bonding compressive strength, resulting in poor bonding; or the printing material used does not match the printing process, resulting in poor bonding.
4. Sticky net
There are many reasons for the sticking of the web: because the printing material is affected by the working pressure and temperature, which causes the web to stick to the web; or because the screen printing standard is changed, the printing material is too thick to cause the web to stick.
5. Needle eyes and blisters
The eye of the needle problem is one of the most important inspection items in quality control. The causes of pinholes are: a. Dust and dirt on the screen lead to pinholes; b. The surface of the pcb board is polluted by the environment; c. There are bubbles in the printing material. Therefore, it is necessary to carry out a careful inspection of the screen version, and find that the pinhole is repaired immediately.
The above are some common fault analysis of PCB circuit board screen printing, have you learned it?