What are the common faults of PCB screen printing?

PCB screen printing is an important link in the PCB manufacturing process, then, what are the common faults of PCB board screen printing? 

1, The screen level of the fault  

1), plugging holes   

The reasons for this kind of situation are: printing material dry too fast, in the screen version dry hole, printing speed is too fast, scraper strength is too high.  Solution, should use volatile slow organic solvent printing material, with a soft cloth dipped in organic solvent gently cleaning screen.  

2), screen version ink leakage  

 Causes of this kind of failure are: PCB board surface or printing material in dust, dirt, screen printing screen plate damage; In addition, when printing plate making, screen mask glue exposure is not enough, resulting in screen mask dry solid is not complete, resulting in ink leakage.  The solution is to use tape paper or tape to stick on the small round hole of the screen, or repair it with the glue of the screen. 

3), screen damage and precision reduction  

 Even if the quality of the screen is very good, after long-term application, due to the damage of the plate scraping and printing damage, its precision will slowly reduce or damage.  The service life of the immediate screen is longer than that of the indirect screen, generally speaking, the mass production of the immediate screen.  

4), printing pressure caused by the fault  

Scraper pressure is too large, not only will make the printing material through a large amount, resulting in scraper bending deformation, but will make the printing material through less, cannot screen printing a clear image, will continue to cause scraper damage and screen mask down, wire mesh length, image deformation 

2, PCB printing layer caused by the fault  

 

1), plugging holes  

 

The printing material on the screen will block part of the screen mesh, leading to the part of the printing material through less or not at all, resulting in poor packaging printing pattern.  The solution should be to clean up the screen carefully.  

2), PCB board back is dirty printing material  

Because the printing polyurethane coating on THE PCB board is not completely dry, the PCB board is stacked together, resulting in the printing material sticking to the back of the PCB board, resulting in dirt. 

3). Poor adhesion  

The former solution of PCB board is very harmful to the bonding compressive strength, resulting in poor bonding; Or the printing material is not matched with the printing process, resulting in poor adhesion.  

4), the twigs  

There are many reasons for adhesion: because printing material by the working pressure and temperature harm caused by adhesion; Or because of the transformation of screen printing standards, printing material is too thick resulting in sticky mesh.  

5). Needle eye and bubbling  

Pinhole problem is one of the most important inspection items in quality control.  

The causes of pinhole are:

a. Dust and dirt on the screen lead to pinhole; 

b. PCB board surface is polluted by environment;  

c. There are bubbles in the printing material.  

Therefore, to carry out careful inspection of the screen, found that the eye of the needle immediately repair.