Interface‐Controlled Reliability of HDI Microvias: A Critical Review and Perspective

High‐density interconnect (HDI) microvias are foundational to modern information technologies, enabling high‐density routing in advanced computing, 5G, automotive, and aerospace electronics. As microvia dimensions shrink and stacked architectures become ubiquitous, reliability gains have stagnated despite continued geometric optimization. Growing evidence shows that reliability in advanced HDI microvias is increasingly governed by the coupled effects of via geometry, materials selection, and time‐dependent degradation at the buried electroless–target copper interface, where nanoscale void nucleation, progressive interfacial decohesion, and locally thinned copper layers control damage evolution and early failure. This interface constitutes a heterogeneous copper material system whose microstructure and bonding integrity are critically shaped by manufacturing physics, including laser drilling, surface conditioning, seed‐layer continuity, and electroplating dynamics, yet remain weakly represented in geometry‐focused qualification standards. Recent advances in nondestructive evaluation, data‐driven defect analysis, and physics‐informed modeling now enable progressive interface degradation to be detected, characterized, and assessed prior to field exposure. Treating the electroless–target interface as a functional materials system and a primary design variable provides a pathway toward predictive, mechanism‐based reliability frameworks for next‐generation electronic substrates.