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.
Interconnect Connection Defect
Structural Continuity
Metallic discontinuity within a high-density vertical pathway prevents the electrical transition between conductive layers of a printed circuit board. An interconnect connection defect interrupts the signal path due to barrel cracking, plating voids or improper pad-to-trace integration. This physical separation prevents charge transfer across layers and results in an open circuit at the site of the transition.
The failure persists even if the surface pads maintain visual contact because the internal barrel integrity remains insufficient to sustain current.
Inspection Modality
Automated optical inspection and cross-section analysis verify the structural state of the via at the post-lamination stage. A technician identifies the interconnect connection defect by measuring electrical resistance through the vertical pathway during an in-circuit test. High impedance readings across the barrel demonstrate that the material contact is insufficient to bridge the dielectric gap.
Resistance measurements vary according to the geometry of the via and the thickness of the copper deposition.
Operational Consequence
Thermal cycling induces mechanical stress on these junctions because copper and the surrounding laminate expand at different rates. The interconnect connection defect propagates during these temperature fluctuations as the barrel wall separates further from the pad or fractures along the drill axis. Electronic systems fail when the internal signal path snaps, causing intermittent malfunctions or permanent loss of communication between board layers.
A latent break typically forces the rejection of an entire assembly.