Microvia Target Pad Interfacial Separation under Reflow Thermal Stress
Microvia target pad separation stems from z-axis thermal expansion strain exceeding electroless copper interfacial bond strength during assembly reflow.
Microvia Base Crack
Structural Integrity
A vertical separation occurring at the junction between the copper plating of a blind via and the copper pad of the underlying layer describes a microvia base crack. High thermal stress during reflow soldering often causes this mechanical failure. Different coefficients of thermal expansion between the dielectric material and the copper structures generate intense localized strain.
Such strain exceeds the ductility limits of the thin copper deposit. Repeated heating cycles propagate the initial discontinuity through the full thickness of the base metal.
Mechanical Determinant
The failure mechanism originates from inadequate plating thickness or poor copper adhesion at the interface. Manufacturers monitor these geometries through cross sectional analysis of production coupons. High magnification inspection identifies the horizontal fissure along the transition zone.
Failure to maintain uniform plating chemistry leads to grain boundary weakness in the electrodeposited copper. Corrective actions involve adjusting the pulse plating parameters to increase metal density.
Acceptance Boundary
Performance standards disqualify assemblies showing any separation that compromises electrical continuity. Reliability testing requires rigorous thermal cycling to detect latent fractures invisible to standard optical inspection. These discontinuities eventually lead to open circuits in dense interconnect architectures.
A compromised base structure inevitably results in total loss of signal integrity within the affected interconnect.