Definition

Bow and twist are measurements of PCB flatness. Bow is the deviation where a board is cylindrically curved (edges curve up while center remains flat, or vice versa). Twist is the deviation where one corner lifts relative to the other three corners. IPC specifies maximum allowable bow and twist (typically 0.75% for surface mount, 1.5% for through-hole). Excessive warpage causes assembly problems: solder paste printing issues, component placement errors, and solder joint opens. Symmetric stackups and proper material handling minimize warpage.