Wicking phenomenon, also known as core pulling phenomenon, is one of the common welding defects, which is more common in gas phase reflow welding. The wicking phenomenon causes the solder to escape from the pad and travel up the lead to between the lead and the chip body, usually resulting in a serious virtual soldering phenomenon. The reason for this is as long as the thermal conductivity of the component pins is large, so the temperature rises rapidly, so that the solder preferentially wets the pins, and the wetting force between the solder and the pins is much greater than the wetting force between the solder and the pads. Upturning will exacerbate the wicking phenomenon.

Solution：

3.1 For gas phase reflow soldering, the SMA should be fully preheated first and then put into the gas phase furnace;

3.2The solderability of the PCB pads should be carefully checked, and PCBs with poor solderability cannot be used for production;

3.3 Pay full attention to the coplanarity of components, and devices with poor coplanarity cannot be used for production.

In infrared reflow soldering, the organic flux in the PCB substrate and solder is a good absorption medium for infrared rays, but the pins can partially reflect infrared rays, so the solder melts preferentially, and the wetting force between the solder and the pad is less Will be greater than the wetting force between the solder and the lead, so the solder will not rise along the lead, so the probability of wicking is much smaller.