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.
Uncovered Nets
Copper Exposure
Exposed conductive features on a printed circuit board denote areas where the dielectric substrate lacks the required protective solder mask layer. Uncovered nets occur during the fabrication process when liquid photoimageable solder mask fails to bridge narrow gaps between traces or over copper features due to improper registration or inadequate volume. This condition exposes bare metal to oxidation, moisture ingress and potential bridging by external contaminants during assembly or service.
Process Variation
Precision photolithography ensures that mask openings align with copper patterns within specific positional tolerances to prevent accidental exposure of active signal paths. Variations in the alignment of the stencil or film relative to the underlying copper geometry create situations where uncovered nets breach the isolation requirements of the design. Technicians inspect these deviations under magnification to determine if the exposed area risks electrical shorting or signal degradation under load.
Factors such as solder mask shrinkage during the curing cycle or over-etching of the copper traces frequently contribute to these geometric mismatches.
Manufacturing Constraint
Engineering specifications define the minimum allowable distance between a solder mask opening and a copper feature to maintain reliable board performance. Production lines manage these clearances by applying strict tolerances to the alignment equipment and adjusting the viscosity of the mask material to facilitate complete coverage. When the mask layer remains insufficient to bridge the gap between traces, the resulting physical discontinuity represents a latent failure point that compromises the electrical integrity of the entire finished product.