Bow means the board curves like a shallow dish or a section of tube while its four corners still sit on one plane; twist means it is wrung along a diagonal so one corner rises off the plane of the other three. Both are measured as a percentage of the board length or diagonal, and IPC-6012 caps them at 0.75 percent for boards with surface mount parts and 1.5 percent for others. Unbalanced stackups, uneven copper and thin panels in reflow are the usual causes, and warpage drives defects such as head-in-pillow.
Bow and twist is over 1 percent on the thin panels, add a stiffener rail or run them in a reflow carrier.
Also heard as
- warp
- warpage
Related terms
Stackup
Ordered arrangement of copper layers, cores and prepregs that makes up a multilayer board, with each thickness.
Head-in-pillow
BGA defect where a solder ball rests in melted paste but never fuses with it, leaving a hidden weak joint.
Panelization
Arranging several boards on one production panel so they are fabricated and assembled together.