Rigid Flex Stackup Selection against Discrete Board Interconnects
Rigid-flex stackup selection replaces failure-prone discrete connectors with continuous polyimide trace runs, trading lower bare-board cost for reliability.
Plated through Hole Barrel Crack
Mechanical Stress
Axial elongation along the copper wall arises during thermal excursions because the coefficient of thermal expansion along the z axis exceeds the expansion rate of the substrate material. Plated through hole barrel crack develops when mechanical strain from high temperature reflow exceeds the ultimate tensile strength of the deposited copper. Microsection analysis reveals transverse or horizontal separations within the copper deposit along the vertical walls of the interconnection.
Fabrication Defect
Electroplating chemistry anomalies during board production lead to uneven copper deposition and localized thinning inside the vertical interconnect. Plated through hole barrel crack originates at sites where organic addition agents co deposit into the metal structure and create internal voids during subsequent heat treatments. Process control parameters including current density and bath agitation require strict monitoring to prevent high stress grain structures from forming during the metallization cycle.
Thermal Audit
Resistance measurements taken during accelerated temperature cycling detect intermittent continuity failures caused by structural separations inside the circuit board. Plated through hole barrel crack grows progressively under cyclic loading until total electrical open failure occurs during assembly or field operation. Microscopic examination of cross sectioned coupons after thermal shock testing confirms the mechanical integrity of the vertical copper wall.