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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 (BGA)terminations. Excessive voiding will reduce joint pull strength it does not necessarily reduce the reliability of the joint

Figure 1: Excessive voiding reduces joint pull strength, but doesn't necessarily reduce joint reliability.

Chip Leaching	Component Cracking	Cracked Joint	Crystallized Joints	Failure to Reflow
Joint Failure	Joint Voiding	Lifted Component	Open Joints	PCB Measelling
Plastic Coplanarity	Plastic Softening	Poor Pad Wetting	Poor Solderability & Wetting	Solder Beading
Solder Short	Solder Wicking