Voiding is the presence of cavities in solder joints, formed when flux volatiles and gases cannot escape before the solder freezes. Large thermal pads under QFNs and power parts suffer most, along with BGA balls and unfilled via-in-pad. Acceptance limits for BGA balls sit at 25 to 30 percent of the ball area on X-ray, while thermal pads are judged by their effect on heat transfer. Window-pane stencil apertures, vacuum reflow and profile changes cut it down.
X-ray shows 40 percent voiding under the MOSFET thermal pad, split the stencil aperture into a window pane.
Also heard as
- voids
- solder voids
Related terms
Via-in-pad
Via placed directly in a component pad, filled and plated over so solder cannot drain down it.
Reflow
Soldering surface mount parts by melting printed solder paste in an oven that follows a set temperature profile.
Head-in-pillow
BGA defect where a solder ball rests in melted paste but never fuses with it, leaving a hidden weak joint.
Stencil
Thin laser-cut metal sheet used to print solder paste onto board pads before parts are placed.