Solder Continuity
Unintended conductive paths formed by molten solder connecting two or more adjacent conductors during the assembly process describe a common defect. While bridging often occurs during the stencil printing phase due to paste slump, it typically solidifies during reflow to create a short circuit. This condition violates the isolation requirements of IPC-A-610 standards.
Deposition Control
Solder paste volume and placement accuracy determine the likelihood of such connections. Excess paste or misaligned apertures cause the material to squeeze out between pads under the weight of the component. Thin stencils reduce the available material to prevent overflow.
Fine-pitch components with spacing below 0.5 mm require precise stencil tension to maintain separation.
Post-Reflow Inspection
Automated optical inspection systems identify these shorts by comparing the captured image against a golden board or CAD data. If a bridge remains undetected, it leads to electrical failure or thermal damage when the assembly is powered. Manual rework involves removing the excess solder with a braid or specialized vacuum tool.
Verification of the repair ensures no residual conductive beads remain on the substrate. The inspector must confirm that the underlying solder mask was not scorched during the desoldering process because damaged mask allows future migration. High-reliability applications often demand x-ray inspection to check for hidden shorts under ball grid array packages where optical lenses cannot reach.
