Structural Fracture
Fatigue failures within the copper plating of a vertical interconnect access point compromise the electrical path between board layers. Via barrel cracking occurs when the copper wall of a hole breaks, typically along the circumference, due to the expansion and contraction of the surrounding material. This issue often results in intermittent signals or complete circuit failure after the board has been in the field.
Material Stress
The mismatch between the coefficient of thermal expansion of the copper and the epoxy resin is the primary driver of this defect. During soldering or operational heating, the laminate expands much faster in the vertical direction than the copper plating can stretch. This tension results in via barrel cracking by stressing the thin metal wall at its weakest point.
Thicker plating can mitigate this risk, but it is harder to achieve in very small holes or high-aspect-ratio designs. Designers often specify high-performance laminates with lower expansion rates to protect the integrity of the vias in harsh environments. Failure is most common during the thermal shock of wave soldering or when the device undergoes rapid temperature swings in use.
Detection Method
Micro-sectioning and thermal cycling tests are used to identify the presence of these cracks. Because the breaks are often microscopic, they may not be visible on a standard X-ray.
