Why does the PCB's insulating green paint peel off when the PCB is in an automatic tin furnace?

Why does the PCB's insulating green paint peel off when the PCB is in an automatic tin furnace?

 

After the PCB is over the automatic tin furnace, the insulating green paint on the under-board line will peel off. Don't know why? What is the reason for S/M Peeling after the gold?

 

There are three major possibilities for green paint peeling. The first is that the green paint itself is not sufficient to withstand the tin furnace test. This may be due to the failure of the green paint to expire or the poor operation. Green paint used by the industry almost always carries out test procedures such as heat resistance and reliability. Therefore, there should be no problem with normality. In this respect, it is necessary to review whether the material itself has changed or the process has changed.

 

The second possibility may be the influence of external force, including flux supply and mechanical collision, especially in the case of high temperature, the green paint characteristics are no longer high hardness like normal temperature environment, and the green paint surface of the circuit board is subjected to any external impact. It is easy to cause scratches and peeling.

 

The third major possibility is that the board is bursting due to moisture absorption before or during storage of green paint. When the water vapor is heated and vaporized, the volume expands nearly three hundred times. The instantaneous temperature rises and the green paint softens. It is easy to cause the green paint to peel off. Such problems may occur in the tin-spraying process of circuit board fabrication, and may also occur in assembly processes such as wave soldering and reflow soldering.

 

There are several possibilities for SMPEELING after gold. The first one may be unsatisfactory treatment in front of copper, the second may be insufficient drying before S/M coating, and the third may be due to excessive stagnation time to produce oxide layer. It may be that the material of the green paint itself is not suitable for the gold process, the fifth may be the lack of polymerization of the green paint. Sixth, if you do more than one high temperature process, such as: gold and gold plating together or two Sub-dip gold may also occur. Because there are many possibilities, you have to do detailed analysis to clarify one by one, but in general it is very important to use the S/M category.

 

Some special green paints react slowly to UV light, requiring anaerobic and relatively high exposure energy to achieve high polymerization. If the degree of exposure polymerization is insufficient, there is no way to achieve the desired polymerization strength after subsequent baking. If you use such materials, you should clearly inform the operator to handle the method correctly, otherwise there will be problems, the above is for your reference.

 

Green paint peeling:

Green paint peeling

 

SMPEELING after gold:

SMPEELING after gold

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