How do you calculate correct length of flex part of a rigid flex structure to allow for minimum bend radius?

FAQ about printed circuit boards › FLEX/RIGID-FLEX

Detailed recommendations can be found in IPC-2223, sections 5.2.3.3 for both static and dynamic bends and should be used for final design verification. However, some basic guidelines based upon the thickness of the flex material can be seen below:

Illustration of a correct length of flex part of a rigid flex structure
FLEX TYPEMINIMUM BEND RADIUS
Single sided flex3 – 6 x circuit thickness
Double sided flex7 – 10 x circuit thickness
Multilayer flex10 – 15 x circuit thickness
Dynamic application20 – 40 x circuit thickness