Why PCB Solder Mask Peeling Off When Welding?

Why the insulation solder mask on the board will peel off after the PCB passes the automatic soldering furnace.

There are three major possibilities for solder mask peeling off:

The first possibility is that the nature of solder mask oil is insufficient to withstand the test of solder furnace. This may be due to the failure of the solder mask oil due to expiration or poor operation.Green Solder mask oil used by the industry are almost always subjected to test procedures such as heat resistance and reliability.Therefore, there should be no problem with normality. In this regard, it is necessary to review whether the material itself has changed or the process has changed.

The second possibility is the influence of external forces,include flux supply and mechanical collisions,Especially under high temperature conditions, solder mask oil properties no longer have a high hardness like normal temperature environment.At this point, the solder mask surface of the circuit board is easily scratched and peeled off by any external force.

The third major possibility is PCB circuit board bursts due to moisture absorption before or when solder mask is applied,Water vapor expands nearly three hundred times in volume when heated and gasified.Instant warming plus green paint softening,It’s very easy to make solder mask peel off.This kind of problem will occur in the process of hot air solder leveling produced by the circuit board, and it may also occur in the assembly processes such as wave soldering, reflow soldering, and so on.

There are several possibilities for SMPEELING after ENIG

• The treatment in front of the copper is not perfect.
• Insufficient drying before S/M coating.
• The stagnation time is too long to generate an oxide layer.
• The material of the solder mask itself is not suitable for the gold process.
• The fifth may be insufficient solder mask polymerization
• More than one high temperature process.For example, gold and gold plating together or gold leaching twice may also occur

There are many possibilities, you have to do a detailed analysis to clarify each item, but in general it is important to use S/M types.Some special solder mask, slow response to UV light,it requires anaerobic and relatively high exposure energy to reach a high degree of polymerization.If the exposure polymerization is insufficient, there will be no way to fully achieve the required polymerization intensity in subsequent baking.If you use such materials, you should clearly inform the operator of the correct method, otherwise the problem will continue.