Common Quality Problems And Improvement Measures In Welding Process Of Custom Pcb

Common quality problems and improvement measures in welding process of custom pcb


1. Exposed copper

The reason:

A. The cleanliness of clean room is not standard.

B. There are debris in the screen, film or exposure glass or Mylar.

C. Clean work is not done well.

Improvement measures:

A. WF screen room and exposure room to be Class 10,000(1 cubic meter of space ≤ 0.5um  dust ion shall be ≤ 10,000. Weekly dust ion test)

B. Two doors of the transfer window cannot be opened at the same time to prevent air from generating convection 

C. Clean room must be positive pressure state. When washing net plate, it must be cleaned according to more than three processes.

D. Check the screen plate before loading, if there is dry ink, wash the net water with the paper to wipe clean.

E. Resistance to soldering field, exposure glass, Mylar as required on the SOP requirements for cleaning.

F. Technician level and above shall be confirmed by needle printing, prevent needle scratch.

 6 layers PCB with BGA for LCD TV.jpg

2. Yellow hole

The reason:

A. The plug hole is not full

B. Or when screen printing the oil ink of the orifice is thin.

Improvement measures:

A. The ink of the plug hole does not allow to add diluent.

B. Select a good thixotropic ink oil to do plug hole.

C. For boards that do not allow holes to be yellowish, when doing plug hole ≥ 80% of the hole diameter . The back should be slightly convex.

D. The viscosity of the plug hole oil ink is controlled above 300 dpa . S .

E. Green oil back washing board,the oil ink in the hole must be vibrated through,then can return the plug hole.

F. When the net is installed, it is carried out with the scrap field, and the position of the silk screen is adjusted accurately.

G. Carefully check the first board and the self - inspection, Do not allow the phenomenon that the plug hole is biased

H.  After the plug hole ,the board should be finished silk screen oil in 15 minutes . Do not stagnate for too long.


3. SM without oil through

The reason:The main parameters of screen printing are inappropriate

Improvement measures:

A. Adjust the appropriate speed, printing pressure, ink viscosity.

B. Use flat blade without concave and convex, and adjust the appropriate angle of attack.

C. Adjust the blade angle, the appropriate network distance.

D. A careful examination of the screen before installing the screen .