Void (connection technology)

As voids , also voids or cavities, called inclusions in the solder joint in the component connections during soldering referred.

Solder paste printing

The solder paste is printed on the circuit board prior to SMD assembly . This is a contiguous area of ​​solder paste.

Melting the solder paste

During the reflow soldering process or vapor phase soldering , the solder paste is heated and the solder components contained in it melt. The flux it contains ensures that the component connection metallization and the copper surface of the circuit board are wetted.

Effect of the flux

The melting solder contracts due to the surface tension and largely displaces the flux contained in it to the outside when it is wetted. Dissolved oxide residues from the connection metallization of the component and the copper surface of the circuit board are also dissolved and displaced to the edge of the soldering point.

Formation of the void

Especially with larger areas, the flux has to cover a further distance from the center of the paste depot to the edge. The greater this distance, the greater the risk that the flux will not be completely displaced by the liquid solder and that it will accumulate as a defect within the actual solder point. Furthermore, the oxides loosened by the flux can collect in this area.

In addition to the inclusion of flux residues and oxide residues within the soldering point, the following effect can also occur. The remaining residues of the flux and oxide residues can, in unfavorable cases, while the solder is liquid, escape explosively. This can result in solder balls , among other things .

Minimizing the risk

The risk of voids can be reduced by printing multiple adjacent small areas of solder paste instead of a single large area of ​​solder paste. The flux contained can escape more easily through the inserted webs.

Furthermore, solder pastes with a lower proportion of flux tend to have less of a tendency to form voids.