Rigid-flex printed circuit boards often differ not only in their application-specific design but also in the stackup and coating of the flex areas. While the rigid areas are covered with a standard green solder resist, as with rigid PCBs, two different coatings are used for the flexible areas: flexible solder resist, or flex mask for short, and Coverlay.
But: What exactly differentiates the two options and when is a choice actually possible?
