Reasons for falling off of green oil in resistance welding of circuit board and what problems will be caused by too thick green oil

Usually, we see a green surface film on the surface of the circuit board. In fact, this is the circuit board solder resist ink. It is printed on the PCB mainly to prevent welding, so it is also called solder resist ink. The most common PCB solder resist inks are green, blue, white, black, yellow and red, as well as a variety of other rare colors. This layer of ink can cover unexpected conductors other than pads, avoid welding short circuit and prolong the service life of PCB in the process of use; It is generally called resistance welding or anti welding; However, during PCB processing, there are many problems from time to time, and one of the most common problems is the drop of solder resist green oil on the circuit board. What is the reason for the drop of ink on the circuit board?

There are three main reasons for the falling off of green oil for resistance welding of circuit board:

One is that when printing ink on PCB, the pretreatment is not done in place. For example, there are stains, dust or impurities on the surface of PCB, or some areas are oxidized. In fact, the simplest way to solve this problem is to do the pretreatment again, but try to clean the stains, impurities or oxide layer on the surface of PCB;

The second reason is that it may be because the circuit board is baked in the oven for a short time or the temperature is not enough, because the circuit board must be baked at high temperature after printing the thermosetting ink. If the baking temperature or time is not enough, the strength of the ink on the board surface will be insufficient, and finally the solder resistance of the circuit board will fall off.

The third reason is the ink quality problem or ink expiration. Both of these reasons will cause the ink on the circuit board to fall off. To solve this problem, we can only replace the ink supplier.

The IPC standard of the circuit board industry does not specify the green oil thickness itself. Generally, the green oil thickness on the line surface is controlled at 10-35um; If the green oil is too thick and too much higher than the pad, there will be two hidden dangers:

One is that the plate thickness exceeds the standard. Too thick green oil thickness will lead to the plate thickness is too thick, which is difficult to install or even can not be used;

Second, the steel mesh is jacked up by green oil during SMT, and the thickness of solder paste printed on the pad is lump by lump, which is easy to cause short circuit between pins after reflow soldering.