Fabrication Defect
Empty spaces within the copper plating of a small laser-drilled hole can compromise the electrical and mechanical reliability of a high-density interconnect. Microvia voids typically form during the electrolytic plating process if air bubbles are trapped or if the chemistry fails to reach the bottom of the hole. These defects are often invisible to surface inspection.
Presence Analysis
Presence of microvia voids reduces the cross-sectional area of the conductor which increases the local current density and resistance. During thermal cycling the air trapped inside a void expands and exerts pressure on the surrounding copper. This stress leads to circumferential cracking or the complete separation of the microvia from the target pad.
Such failures are particularly dangerous because they may appear as intermittent signals during operation rather than an immediate open circuit. Automated X-ray inspection is the primary tool used to detect these internal gaps in a production environment. Process engineers adjust the surfactant levels and agitation in the plating tanks to ensure a void-free fill.
Verification Integrity
Verification of microvia integrity involves cross-sectioning samples from the production lot and performing highly accelerated thermal stress tests. A passing result shows a solid copper structure with no evidence of separation.
