These voids occur when the solder solidifies. Most metals reduce their volume during the transition from the liquid to the solid phase. The missing volume leads to shrinkage in the solder layer during uncontrolled solidification. These shrinkage voids can be recognized as long and thin defects with bulges that run inwards from the edge of the solder layer. Due to their appearance, they are also known as fjord voids, or wormtrenches.

Shrinkage cavities occur more frequently in solder materials with a wide melting range, i.e. when the solidus and liquidus are more than 5°C apart.

Shrinkage cavities can be prevented by directional solidification and/or slower cooling from the peak temperature to the solidus temperature.