Reflow soldering will have various failures during work. Among them, the reflow soldering chip wicking phenomenon is one of the problems. Below, Guang Shengde will briefly analyze the reflow soldering wicking problem.

Reflow wicking

1.The positive temperature of reflow soldering is higher than the back temperature.

In the reflow soldering process, the reflow temperature should be set according to the material, size, component specifications and component density of the PCB. Of course, it also depends on whether it is a double-sided soldering process. If the PCB is thinner and the size is smaller, When doing the double-sided soldering process, a 128PIN or larger QFP must be mounted. This issue must be taken into account when setting the temperature.

Because in the double-sided soldering process, it is necessary to consider that the back component will have high parts or even drop parts due to the secondary reflow. Therefore, the back temperature setting should be slightly lower than the positive temperature. But if the setting is improper, the back temperature is lower than the positive temperature. If the temperature is too much, the result is that the PCB heat is lower, and the component heat is higher. Due to the flow of the solder after melting, the solder will naturally not adhere to the PAD, but to the pins of the QFP with high temperature. When it climbs up, the phenomenon that occurs is that the PAD has less tin and the QFP's pins are bridged and connected to the tin.

2.PAD oxidation.

If the OSP material PCB is not put into production on the BOT surface in time (24 hours) after the TOP surface is completed, then the PAD will be oxidized, and the PAD's ability to eat tin will be severely reduced during soldering. Of course, the solder will climb to the pins of the component. As a result, the pins of the PAD less tin component are connected to the tin.

The above reflow soldering chip wicking countermeasures:

1.When setting the reflow soldering temperature, the difference between the positive temperature and the back temperature is controlled at 15, and the measured temperature difference is controlled at 5 degrees.

2. Use two production lines, and put the BOT surface into production immediately after the TOP surface is completed. If two lines cannot be opened, the produced PCB must be moisture-proof.