What causes solder joint voids in reflow soldering

The purpose of applying solder paste is to evenly apply an appropriate amount of solder paste to the solder pads of the PCB, to ensure that the solder pads corresponding to the SMT components and PCB achieve good electrical connection and sufficient mechanical strength during reflow soldering. Solder paste is a paste made by mixing alloy powder, paste flux, and some additives, which has a fixed viscosity and good tactile properties. At room temperature, due to the fixed viscosity of solder paste, electronic components can be attached to the solder pads of PCBs. When the inclination angle is not too large and there is no external collision, the components generally do not move. When the solder paste is heated to a certain temperature, the alloy powder in the solder paste melts and flows again, and the liquid solder infiltrates the solder ends of the components and the PCB solder pads. After cooling, the solder ends of the components and the solder pads are interconnected by the solder, forming electrical and mechanical solder joints.

Reasons for the formation of voids in reflow soldering operations:

1. The matching relationship between holes and wires is severely imbalanced, and the small wave peak welding of large hole leads almost results in hole phenomena

2. PCB punching deviates from the center of the pad

3. Incomplete solder pads

4. Burrs or oxidation around the hole

5. Lead oxidation, dirt, and poor pre-treatment.