Electrical Shorts
Accidental connections formed by solder between adjacent pads or leads create electrical short circuits that render the circuit board non-functional. The solder bridging defect typically occurs during the stencil printing or component placement stages, where solder paste is smeared between pads. This connection is then melted and solidified during reflow, creating a permanent metallic bridge.
It is one of the most common failure modes in fine-pitch assemblies, requiring manual rework or automated repair. In a production line, these shorts are identified using automatic optical inspection before reflow, or functional testing and x-ray inspection after reflow. Adjusting the stencil print alignment and reducing paste deposit volume are standard ways to minimize this defect.
Solder Mask Integrity
The presence of a solder mask dam between adjacent copper pads acts to prevent molten metal from flowing together. If the spacing between pads is too narrow, a solder mask dam cannot be printed, increasing the likelihood of a bridge forming. This constraint must be considered during the initial design phase of the circuit board layout.
Placement Pressure Effects
Excessive placement force from the pick-and-place machine squeezes the printed solder paste outward, bridging the gap between adjacent pads. Calibrating the height and pressure of the component placement nozzles keeps the paste contained. This pressure adjustment is critical when mounting heavy or fine-pitch components.
