20 – Unevenness of printed circuit boards (twist and warp)

The warp is determined as a percentage of the deflection with reference to the length of the deflected edge, where the four corners of the PCB are lying on a single plane.
To determine the warp, the PCB is placed on an even surface with the convex side uppermost. The largest measured height of the PCB, minus the measured thickness of the PCB – with reference to the length of the PCB – gives the value for the warp.

The twist is defined as PCB deformation along a diagonal or parallel to it. Here, one PCB corner will not be on the same plane as the other three. To determine the twist, the PCB is placed on a level surface with the convex side facing downwards (3 corners in one plane). The maximum height to the level, minus the thickness of the PCB, gives the value for the twist with reference to the diagonal length.

Unless otherwise stated in the order documentation, the maximum permitted value for the warp and distortion is 1,0%.

Warp

Twist

Side view

Determining warp and twist
Warp K is determined as a percentage of the deflection t_k with reference to the length L of the deflected edge:

db electronic

If the deflection occurs both lengthways and crossways, then the larger value shall apply .