Voids are air inclusions or flux or oxide residues that remain in the solder and impair the thermal connection of the component. The blowholes exhibit significantly poorer thermal conductivity than the solder material. The blowholes are detected by X-ray analysis or ultrasound microscopy.

In classic metal processing, voids are referred as defects caused by shrinkage during solidification of the metal – i.e. shrinkage cavities.