Meaning
A manufacturing defect characterized by the presence of small air bubbles or empty spaces inside a solder joint. In surface-mount electronics assembly, solder voiding occurs when volatile gases generated by the solder paste flux are unable to escape before the metal solidifies. Quality control inspectors use x-ray inspection equipment to calculate the total percentage of these voids within the solder joints of critical components.
This phenomenon must be minimized to ensure the mechanical and electrical integrity of the board.
Gas Entrapment
Rapid heating in the reflow oven can cause the flux to boil too quickly, creating pockets of trapped vapor. This is particularly common under large surface-mount packages like ball grid arrays that do not have open sides to vent gases. The size and location of these pockets vary depending on the paste composition and the board finish.
Reliability Consequence
Empty spaces reduce the effective contact area of the solder connection, which raises electrical resistance and decreases thermal conductivity. These hollow spots can also lead to joint cracking under thermal cycling or physical vibration.
Process Optimization
Adjusting the reflow profile to include a longer soak phase gives the volatile components more time to escape before the solder melts. Stencil designs can also be modified to use cross-hatch paste patterns that create escape routes for the gases.