Rigid flex PCB are distinct with their integrated building of both rigid PCB and flex PCB circuits technologies. Being distinct features a variety of distinct needs that must be reviewed and executed during the rigid flex PCB layout phase of the design process.
The first 2 needs relate to minimal room requirements, as gauged to the Flex Transition Area within the design, of plated through holes (PTH) and exterior layer copper functions. The 2nd 2 deal with the mechanical flexibility and integrity of the flex PCB areas when the parts are bent into the called for form.
The Flex To Rigid Transition Areas
The “Flex Transition Zone” is specified as the length of the rigid area lay out at which the layer framework modifications from a rigid location to a flex PCB location only.
The Flex Shift Zone are created by the demand to extend the flex PCB location coverlays by a little range into the rigid areas. This allows the flex coverlays to be captured by the lamination of the rigid area layers and ensure a gapless shift between the flex PCB locations and the rigid locations. The flex coverlays do not extend throughout the rigid areas as needed by IPC 2223C design criterion for flexible PCB.
Layered Via Hole to Flex Transition Area min. spacing = 0.050″
– Makes certain plated through hole integrity by avoiding any type of PTH from being drilled through the flex coverlays as they engage 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 really high co-efficient of thermal growth.
– A plated through opening pierced with a coverlay will go through substantial Z-Axis growth and contraction tension during both the assembly re-flow process and possibly throughout the operation of the finished product. This has actually been determined as a primary root cause of cracked opening layering leading to either prompt product failing or long term latent failure reliability problems.
– This demand is called out in IPC2223C Sec. 22.214.171.124.
External Layer Copper function to Flex Transition Zone minutes. spacing = 0.025″
– Makes certain enough spacing to permit reliable external layer imaging processing.
– Rigid layers, while in production panel configuration and before last lamination process, are required to have the flex PCB locations got rid of. This creates in internal edges, created by the height distinction in between the rigid location and the flex location, which the exterior layer photo transfer movies must transition.
– Min. spacing 025″ offers adequate space for film attachment and a trusted imaging process.
Flex PCB Area Via Holes
– Not advised and will be stayed clear of if design permits.
– Includes significant expense as a result of the extra drilling and layering processes.– Needs blind via manufacturing processes.
Potentially creates mechanical tension concentrators in flex PCB layers which might bring about damage if part is curved in the vicinity of these vias.
– If design does require flex area vias:
-Guarantee vias are located far from the certain bend place(s) in flex areas.
-Have PCB manufacturers testimonial design to assess and establish if any kind of risk variables exist.
Flex PCB Location Trace Layout
-Traces need to be maintained directly and parallel, if design permits.
-If trace direction adjustments are required utilized rounded edges and minimize as long as feasible.
-Aids remove prospective mechanical anxiety concentrators which may bring about breakage when flex PCB location is curved right into setting.
-Stagger traces on surrounding layers, if design enables.
-Improves versatility and reliability by reducing the “I-Beam|” effect of traces positioned directly over one another from layer to layer.