Quantifying Netlist Interconnect Fault Coverage Using Boundary Scan ATPG Vectors
Quantifying boundary scan interconnect fault coverage pairs extracted netlist node universes with modified counting sequence vector execution logs.
Bridging Faults
Solder Connectivity
Electrical conduction between two distinct circuit traces or component terminals occurs through unintended contact of conductive material. Bridging faults represent a physical short circuit caused by excessive solder volume or insufficient clearance between pads during the assembly process. These anomalies create permanent signal paths that bypass designed circuit logic.
Automatic optical inspection systems identify these unwanted connections by scanning for solder extrusions that span the gap between isolated features.
Process Variation
Precision stencil printing and component placement control the occurrence of solder bridges on a printed circuit board. Excess solder paste deposition increases the probability of bridging when reflow temperatures turn the alloy into a liquid state. Fine pitch devices require specific aperture designs to limit the amount of paste applied to individual pads.
Engineers adjust the stencil thickness and stencil opening dimensions to maintain consistent solder volumes. Small gaps between adjacent pads become susceptible to bridging if the solder mask between them lacks sufficient height or structural integrity. Surface tension forces occasionally pull molten solder across the gap toward a neighboring termination.
Electrical Consequence
Current leakage through a bridge changes the expected impedance of a circuit segment and prevents functional operation of the hardware. Signal integrity suffers because low resistance paths redirect voltage into unintended nodes. Microprocessors or logic gates connected to such a bridge often experience permanent damage from drawing excessive current.
Reliability standards categorize these connections as primary failure modes that require immediate rework or board scrapping during production testing. Logic signals that should remain independent become coupled, which leads to incorrect data processing and catastrophic system failure.