Voids in surface mount joints occur due to either volatile gas not escaping or non metallic material not being displaced before the solder solidifies. Basic profiles are provided by the paste suppliers but it is still necessary to make adjustments to these profiles to improve voiding, the visual appearance of the joint surface and the amount of flux left after reflow is complete.

Voids will often be seen under leads, the heel of gull wing leads and in Ball Grid Array terminations. Excessive voiding will reduce joint pull strength it does not necessarily reduce the reliability of the joint.