Case 386 ยท Public preview
Rough Drilled Walls and Thin Copper Can Leave Vias Unable to Survive Z-Axis Expansion
Multiple signal nets opened at plated-through vias that showed no externally visible indication of failure.
Electrical continuity testingMetallographic microsectioningSEMPlating-thickness measurementFailed-to-functional via comparison
What the evidence preview establishes
The vias opened through circumferential barrel cracks near the center PWB layers. Poor drilled-hole quality created stress risers, while copper plating averaging approximately 0.64 mil near the failing region was insufficient to withstand z-axis thermal-expansion stress.
Why this case matters
An externally normal via can contain a mechanically weak barrel. Cross-section failed and nearby functional vias through the board center, then evaluate drilling damage and copper thickness together because rough walls and low throwing power can combine to produce latent opens.
Full evidence reserved for MEMBER and STOREThe complete case includes the evidence sequence, four interpreted figures, alternative explanations, limitations, and practical application guidance.