Interconnect Stress Testing Resistance Drift Correlation with Multilayer PCB Microsections
Interconnect stress testing detects sub-micron post separations through dynamic resistance drift before static optical microsections show physical cracks.
Barrel Fracture
Structural Defect
Metallurgical structural defects in printed circuit board plated through-holes feature complete or partial circumferential copper separation along the via wall. A barrel fracture occurs when differential thermal expansion along the vertical axis forces the electrodeposited copper beyond its tensile ductility limit during thermal shock or reflow processing. Acceptance boundaries defined in IPC-A-600 reject any internal copper crack that reduces the minimum conductor thickness below specified design thresholds.
Thermal Strain
Z-axis movement during assembly reflow generates heavy tensile stress within the copper cylinder as the surrounding organic dielectric expands at rates up to five times greater than the metal. Poor copper elongation properties accelerate crack initiation along internal grain boundaries, especially near mid-plane regions where expansion forces concentrate. Thin electroplated deposits under fifteen micrometres and low-ductility acid copper chemistry increase failure rates under thermal cycling.
Drilling damage, such as gouging or resin smear that leaves an uneven hole wall, creates local stress risers that concentrate mechanical strain. When thermal stress exceeds copper yield strength during wave soldering or assembly rework, microscopic tears propagate circumferentially around the wall perimeter until electrical continuity breaks.
Inspection Criterion
Microsectioning along the via vertical center line provides the definitive test method for identifying internal wall cracks under optical magnification. Thermal stress testing according to IPC-TM-650 Method 2.6.8 forces bare boards through simulated assembly temperatures prior to metallographic polishing. Electrical resistance measurements during thermal cycling detect intermittent open circuits before complete mechanical separation occurs.
A verified barrel fracture requires board scrap or scrap of affected subassemblies because internal plating repairs remain impossible under standard workmanship guidelines.