Material Fracture
Subsurface structural separation occurs within a conductive trace or through-plated hole wall due to thermal fatigue or mechanical stress. A micro-fracture develops when cyclic expansion and contraction exceed the elastic limit of copper deposits during reflow cycles or operating shifts. Small internal ruptures propagate along grain boundaries until electrical continuity fails across the affected segment.
This degradation mode typically appears during automated optical inspection or via cross-sectional analysis in a failure laboratory.
Propagation Mechanism
Temperature fluctuations force the base material to expand at a rate distinct from the plated metal. Differential expansion creates shear forces that pull the interface apart near the substrate anchor points. Constant vibration or high torque during fastener installation accelerates the separation process along the barrel of a via.
Small fissures initiate at the thinnest portion of a plating void or where copper thickness falls below design specifications.
Detection Standard
Electrical testing captures open circuits when the separation prevents current flow through the path. Automated probes identify high resistance signals that suggest internal discontinuities. Advanced imaging techniques show the path of the crack through the crystalline structure of the conductor.
Visual inspection often fails to identify the condition because the outer surface remains intact despite internal damage. Permanent degradation of the physical link dictates the effective lifespan of the assembly.
