Short Anomaly
Defective chemical etching or mechanical foil handling during multilayer circuit board fabrication causes unintended copper connections between adjacent internal traces. An inner layer copper bridge forms an electrical short circuit buried within the solid dielectric core of an unpopulated board laminate. This shorting fault disrupts signal distribution and causes power supply overload when the circuit assembly powers up.
The scope of this defect definition excludes outer layer copper bridges created by solder bridging during surface mount assembly processes.
Formation Mechanism
Photolithographic imaging failures, such as airborne dust particles on photoresist artwork or incomplete resist development, leave residual photoresist strips over copper foil surfaces. During subsequent acid etching baths, the protected copper regions remain unetched, leaving narrow metallic filaments between closely spaced conductor paths. When inner layers undergo oxide treatment and press lamination, these metallic bridges become permanently embedded within fiberglass epoxy dielectric matrices.
High-voltage electrical testing identifies these low-resistance bridges before drilling and surface plating steps occur. Automated optical inspection systems scan inner layer cores prior to lamination, flagging residual copper features that violate design spacing rules.
Screening Test
Flying probe testers and bed-of-nails continuity fixtures detect buried electrical shorts during post-fabrication quality screening. Residual copper bridging that escapes optical inspection creates catastrophic board failures during final assembly burn-in testing. High-potential dielectric withstand testing verifies that adjacent isolated networks retain required insulation resistance under high voltage stress.
