 Microvia reliability research has focused on experimental assessment of the reliability of single-level unfilled microvias, as well as finite element analysis on stress/strain distributions in single-level microvias and microvia fatigue life estimation.Microvia failures identified from the research include interfacial separation (separation between the base of the microvia and the target pad), barrel cracks, corner/knee cracks, and target pad cracks (also referred to as microvia pull out).These failures result from the thermomechanical stresses caused by coefficient of thermal expansion (CTE) mismatch, in the PCB thickness direction, between the metallization in a microvia structure and the dielectric materials surrounding the metal.