Rigid flex PCB are special with their incorporated building of both rigid PCB and flex PCB circuits innovations. Being unique includes a number of special needs that should be examined and carried out throughout the rigid flex PCB layout stage of the design process.
The first two requirements relate to minimum area demands, as measured to the Flex Transition Zone within the design, of plated through openings (PTH) and exterior layer copper features. The 2nd two handle the mechanical flexibility and integrity of the flex PCB locations when the components are bent into the required form.
The Flex To Rigid Transition Zones
The “Flex Transition Zone” is specified as the size of the rigid area outline at which the layer framework modifications from a rigid area to a flex PCB area only.
The Flex Change Area are produced by the need to expand the flex PCB location coverlays by a tiny range right into the rigid areas. This allows the flex coverlays to be caught by the lamination of the rigid location layers and make certain a gapless shift in between the flex PCB areas and the rigid locations. The flex coverlays do not expand throughout the rigid locations as called for by IPC 2223C design criterion for flexible PCB.
Layered With Opening to Flex Transition Area min. spacing = 0.050″
– Ensures layered with opening integrity by protecting against any PTH from being drilled via the flex coverlays as they involve and are captured by the Rigid location layer lamination.
– Coverlays are laminated to the flex PCB layers utilizing a flexible adhesive, either acrylic or epoxy based. These adhesives have a very high co-efficient of thermal growth.
– A plated via hole pierced with a coverlay will certainly undergo considerable Z-Axis growth and contraction anxiety during both the assembly re-flow process and possibly throughout the procedure of the finished product. This has actually been determined as a key source of broken opening layering resulting in either instant product failing or long-term latent failing integrity problems.
– This requirement is called out in IPC2223C Sec. 18.104.22.168.
Exterior Layer Copper feature to Flex Transition Zone min. spacing = 0.025″
– Makes sure enough spacing to allow for reliable outside layer imaging processing.
– Rigid layers, while in production panel arrangement and prior to final lamination process, are called for to have the flex PCB areas got rid of. This develops in inner sides, created by the height difference in between the rigid area and the flex location, which the exterior layer image transfer films need to transition.
– Min. spacing 025″ supplies enough area for film attachment and a dependable imaging process.
Flex PCB Location Via Holes
– Not suggested and should be stayed clear of if design permits.
– Includes substantial cost as a result of the extra drilling and layering processes.– Requires blind via manufacturing processes.
Possibly creates mechanical stress concentrators in flex PCB layers which may cause breakage if part is bent in the vicinity of these vias.
– If design does need flex area vias:
-Make certain vias lie away from the certain bend place(s) in flex areas.
-Have PCB supplier review design to assess and determine if any risk aspects exist.
Flex PCB Location Trace Layout
-Traces ought to be maintained directly and parallel, if design enables.
-If trace direction adjustments are required utilized curved corners and minimize as much as feasible.
-Aids get rid of possible mechanical tension concentrators which could bring about breakage when flex PCB area is curved right into placement.
-Stagger traces on surrounding layers, if design permits.
-Improves adaptability and integrity by reducing the “I-Beam” impact of traces placed straight above one another from layer to layer.