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The relationship between residual debris and humidity after lead-free solder paste soldering

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Update time : 2022-11-10 10:47:33
In order to further improve the soldering effect, flux must be added to the solder paste. However, due to the active ingredients of the flux and acidic liquids such as organic acids, there will be corrosive problems after the soldering process. If it is not cleaned, it may lead to to component safety and reliability. Among such acidic liquids, "weak organic acids" are relatively common, such as carboxylic acids, which are polar compounds and have certain compatibility with water. In the reflow soldering process, a large part of the organic acid will be disassembled after being subjected to the effect of high temperature, but there will still be a very small amount of residue on the underside of the PCBA device, which will absorb the moisture of the ring mirror and convert it into corrosiveness during aging. liquid.
In view of the loss caused by the conversion of corrosive residues to temperature and humidity, some scientific research and technical personnel used acidity display gel to do a test test. These kinds of lead-free solder pastes were selected for scientific experiments, and the experiments were conducted under different temperature and humidity. Derivation of active agents.
R&D process:
Immediately after welding:
Acidity shows that the gel can react with acid and is marked red, so it is often used to determine the presence of acidic corrosive compounds. After seeing the acidity of these lead-free solder pastes just after the soldering process, slight coloring can be observed, but because the soldering process is just performed, the acidity remains relatively small.
The solder joints that have just been welded and processed:
Loss due to working ambient temperature at low working ambient temperature:
After 14 days in a low working environment temperature environment, the red circle can be clearly felt from the details. In addition, in the case of a very low working environment temperature of 60%RH, the ambient humidity and the time of exposure do not have a significant effect on the amount of residues around the solder joints.
Solder joints after 14 days at low operating ambient temperature:
Loss due to working ambient temperature at high working ambient temperature:
After being placed in the same working environment for 14 days, these lead-free solder pastes also have the problem of short-term retention. Specifically, the working environment temperature can also lead to the existence of residues. Under the precondition of the same working environment temperature, the residue film will also crack, and the acid liquid may be transformed. At the same time, the effect of high ambient humidity on the derivative of the residue becomes somewhat obvious, and a better working temperature will cause more obvious residue film cracking.
Solder joints after 14 days at working ambient temperature:
Experimental results:
The hygroscopicity of lead-free solder paste as acidic residue makes it immersed in humid weather and tends to transform into a thicker acidic water film on the surface of the PCB board. The water mist has good electrical conductivity, which greatly increases the possibility of electric leakage at the welding process, thus causing the pcb board to be corroded.
Aggressive residues are converted to less in the case of too low humidity. Similarly, there are more residues at high working ambient temperatures. Thus, the high operating ambient temperature environment is a major factor in the formation of aggressive deposits. For this precondition, the loss caused by the working ambient temperature becomes more intuitive. Therefore, after soldering, you need to pay attention to quickly clean up the residual debris, or use no-clean solder paste directly.
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