PCB Tech - What are the reasons for the peeling off of the solder mask green oil on the circuit board? What are the precautions for using the circuit board ink?

We usually see a green film on the surface of the circuit board. In fact, this is a circuit board solder resist ink. It is printed on the PCB to prevent soldering, so it is also called solder resist ink. Let's talk about the reasons for ink shedding during production and the precautions for use.

Reasons for the green oil falling off the circuit board:
1. When the PCB is printing ink, the pre-treatment is not in place. For example, there are stains, dust or impurities on the surface of the PCB, or some areas are oxidized. In fact, it is very simple to solve this problem. Just do the pre-treatment again, but It is necessary to clean up the stains, impurities or oxide layer on the surface of the circuit board. This is caused by the mistakes in the operation of the production staff and the lack of strict management.

2. The baking time of the circuit board is short or the temperature is not enough, because the circuit board must be baked at a high temperature after printing the thermosetting ink, and if the baking temperature or time is insufficient, the strength of the board surface ink will be insufficient. The subsequent process flowed down and the final product was shipped. The customer received the board for patch processing. The high temperature of the tin furnace during the patch processing caused the ink on the circuit board to fall off.

3, ink quality problems or ink expired, or purchase of unknown brand ink, this will also cause the circuit board ink to fall when passing through the tin furnace. In some small board factories, the purchased ink has not been used up for a long time, and the color of the ink is different after repeated use, the performance is also greatly reduced, and the ink is more likely to fall off.

Precautions for using circuit board ink
1. Temperature requirements. In any case, the temperature of the ink must be kept below 20-25°C, and the temperature cannot change too much, otherwise it will affect the viscosity of the ink and the quality and effect of screen printing. Especially when the ink is stored outdoors or at different temperatures, it must be placed in the ambient temperature for a few days before use or the ink tank can reach a proper operating temperature.

This is because the use of cold ink will cause screen printing failures and cause unnecessary trouble. Therefore, in order to maintain the quality of the ink, it is best to store or store in the process conditions at room temperature.

2. The ink must be manually or mechanically stirred evenly before use. If air enters the ink, let it stand for a period of time when using it. If you need to dilute, you must first mix it thoroughly, and then check its viscosity. The ink tank must be sealed immediately after use. At the same time, never put the ink on the screen back into the ink tank and mix with the unused ink.

3. It must be equipped with a special cleaning agent for ink cleaning, and it must be very thorough and clean. No matter what color the ink is, it must be cleaned once. It is best to use a clean solvent, so that it will not affect the use of other colors of ink.

4. When the ink is dried, it must be done in a device with a good exhaust system to ensure that the quality of the ink will not change significantly.