Design Requirements about Rigid-Flex PCBs
Rigid-flex printed circuit boards are unique in terms of integrated construction of both rigid and flex circuit technologies. Unique construction comes with unique requirements that should be reviewed and implemented during the rigid-flex PCB Gerber layout phase of the design process. In this article, regulations deal with the mechanical flexibility and reliability of the flex areas when the parts are bent into the required shape are outlined.
External Layer Copper
a. 025” min. spacing is the best design offering sufficient space for film adhesion and a reliable imaging process.
b. Min. spacing between external layer copper to flex transition zone is 0.025”.
c. Sufficient spacing is a must to allow for reliable external layer imaging processing.
d. Rigid layers, while in production panel configuration and prior to final lamination process, are required to have the flex areas removed. This creates in internal edges, created by the height difference between the rigid area and the flex area, which the external layer image transfer films must transition.
Trace Layout ，
a. Keep traces straight and parallel can eliminate potential mechanical stress concentrators which may lead to breakage when flex area is bent into position.
b. Keep stagger traces on adjacent layers can improve board’s flexibility and reliability.
a. It is better to avoid via holes in your flex circuit area.
b. If you really needs, please ensure vias are located away from the specific bend location in flex sections, and let your manufacturer review your design to evaluate if any risk factors exist.
c. Potentially creates mechanical stress concentrators in flex layers which may lead to breakage if part is bent in the vicinity of these vias.