Definition

A barrel crack is a fracture in the copper plating wall of a plated through-hole, typically caused by Z-axis thermal expansion mismatch between the plating and laminate. During thermal cycling, the laminate expands more than the copper barrel, creating tensile stress that can crack the plating. Barrel cracks cause intermittent opens or increased resistance. Risk factors include high aspect ratio, thin plating, thick boards, and numerous thermal cycles (especially above Tg). High-reliability designs specify minimum plating thickness and controlled CTE materials.