A brief discussion on the relationship between residual impurities and humidity after lead-free solder paste soldering?

In recent years, the temperature environment in the south has been variable. The influence of many factors such as the manufacturing process design of electronic components and user demands has also attracted widespread attention. Today, the solder paste manufacturer will lead everyone to understand the relationship between the residual impurities after solder paste soldering and humidity.

To further enhance the soldering effect, flux is always added to the solder paste. However, due to the active active ingredients and acidic liquids such as organic acids in the flux, corrosive problems may occur after the soldering process. If not cleaned, it may affect the safety and reliability of the components. Among such acidic liquids, "weak organic acids" are relatively common, such as carboxylic acids, which are polar compounds and have a certain degree of solubility in water. During the reflow soldering process, after being exposed to a relatively high temperature, a large part of the organic acids will be separated, but there will still be a very small amount of residuePCBAThe lower side of the device will absorb moisture from the mirror and turn into corrosive liquid as it ages.

In response to the losses caused by the transformation of corrosive residues due to temperature and humidity, some scientific researchers and technicians conducted an experiment using acidity display gel. The scientific experiment selected these lead-free solder pastes to test the evolution of active agents under different temperature and humidity conditions.

Research and development process

Just after the welding processing:

The acidity indicator gel can react with acid and is marked in red, and thus is often used to determine whether acidic corrosive compounds exist. The acidic display of these lead-free solder pastes right after the soldering process can already show subtle discoloration. However, since the soldering process has just been carried out, the acidic residue is always relatively small.

The weld points just welded and processed:

Losses caused by working environment temperature at low working environment temperature:

Place in a low working environment temperature environment14Within a day, it can be clearly felt from the details that a large number of red circles have been added. Besides, in60%RHUnder extremely low working environment temperatures, environmental humidity and the time of placement do not have a significant effect on the quantity of residues remaining around the solder joint.

Placed in a low working environment temperature14The welding points of Tianhou:

Losses caused by working environment temperature under high working environment temperature:

It was placed under the same working environment temperature14Within a few days, these several types of lead-free solder pastes also experienced the problem of residual substances forming over a short period of time. Specifically, the working environment temperature can also lead to the presence of residues. Under the same working environment temperature conditions, the remaining film may still crack, and acidic liquids may undergo transformation. At the same time, the effect of high environmental humidity on the evolution of the retained substances becomes somewhat obvious, and a better working temperature will cause relatively obvious cracking of the retained substance film.

Set it at the working environment temperature14The welding points of Tianhou:

Experimental result:

Lead-free solder pasteThe hygroscopicity of acidic residues often causes them to be soaked in damp weatherpcbThe surface of the plate transforms into an additional layer of relatively thick acidic water film. This water mist has good electrical conductivity, which significantly increases the possibility of leakage at the welding processing site, thereby causingpcbThe board is corroded.

Under conditions of excessively low humidity, the transformation of corrosive residues is relatively small. Similarly, there are more residues at high working environment temperatures. Therefore, a high working environment temperature is a major factor in the formation of corrosive residues. For this prerequisite, the loss caused by the working environment temperature becomes more and more intuitive. Therefore, after welding, it is necessary to pay attention to quickly cleaning up the remaining debris, or directly use the no-cleaning solder paste.