Are you considering making use of a rigid flex PCB for an application? If so, the first and also most evident answer to the question ‘why?’ is to make use of the adaptability and to permit motion between 2 conventional boards– even if the movement is restricted to supplying vibration resistance.
Flex circuits that actually flex in routine use can, nevertheless, be considered a special case; quite typically, the intent is to offer an effective interconnect between two boards that do not lie in the same airplane. In such situations, the flexible part could just flex during last assembly of the item and also never do so again.
Rigid flex PCB can be considered as an alternate interconnect technique or as wire substitute. One flexible circuits section replaces, at a minimum, a cable television plus 2 connectors– which may be worthwhile for expense of products factors– as well as releases the quantity the adapters would certainly have occupied. This is significant for such products as wearables, where every mm3 within the enclosure is made use of, as well as in systems where two or more PCBs must be folded into area in last assembly. PCB makers report that products where area and also weight go to a costs are among the fastest growing adopters of rigid flex PCB technology
Other advantages include: boosted reliability, with fewer ports and linked solder joints; and also control of the signal path in between the wiring on the boards at either end of the flex.
Today, the design procedure is assisted by 3D capable PCB design software program; if you are attempting to make optimal usage of space, you need to ensure there is no disturbance in between part profiles. Progressively, design software application can likewise model the flexed state of the non rigid part to establish parameters such as bend span– as well as do so dynamically, to check the entire path of system where the two rigid elements move, in normal use.
Fully grown modern technology.
Rigid flex PCB fabrication is a fully grown modern technology, with well developed regulations for success. The very first is to develop and also keep a dialogue with the rigid flex PCB manufacturer and to guarantee that any type of adjustments to design guidelines or design checks (DRC) are imported right into the layout plan being used and followed.
A number of the standards for an effective result of a rigid flex PCB design circulation from the properties of the products being used. The base material for the stiff part is most likely to be FR4, while the flex is usually a polyimide film (typically called Kapton, after DuPont’s material) with copper aluminum foil applied and a coverlay film imposed in place of the solder mask.
Some idea is required concerning how the material homes match the activity as well as this promptly reveals where care must be taken. The copper-to-film bond is a junction in between different products; the tighter the bend distance, the greater the stresses at the limit as well as the greater the danger of delamination. The tracks, although slim, are copper and if the bend radius is too small, repetitive flexing brings the risk of stress fracture.
The transition between stiff as well as flexible circuits is additionally an essential area; just like cable television discontinuation, flexing forces must not be imposed at the transition as this could produce really small bend radii over a small distance. Once again, dynamic modelling of folding in 3D is useful as well as the make-up of the layer rigid flex PCB stack-up is crucial for integrity and manufacturability.
Several usual errors can be prevented by focus on a few bottom lines in the design procedure. One aspect is the need for a bigger copper ring around any opening drilled in the flex as well as, as a relevant point, the need to leave a larger splitting up between drill hole/pad as well as surrounding tracks. The flexible circuits movie is simply that and the impact of that adaptability is to raise normal (unavoidable) resistances. Therefore, if a drilled hole misses out on concentricity with its pad by a small margin, the hole will certainly still plate as well as connection through the via will be untouched– yet there is a danger of a brief to a track passing also close.
Reducing vias in the flex circuits region is preferable in itself; the expense of vias is more than in the inflexible, presuming the design needs a double sided flex circuits. This is one area where the configuration of the rigid flex PCB stack-up that comprises the full PCB is essential. The rigid flex PCB manufacturing procedure remains in component subtractive– there will be layers over and under the flex in fabrication that are gotten rid of uniquely to release the flex circuits segment prior to the process is full. The stack-up must be set up to make sure the polyimide layer is completely sustained with any boring. Visualising a drill little bit attempting to pass through a thin, deformable movie will immediately reveal why.
Transition
Merely taking vias in the flexible location back right into the inflexible part– the flex layer runs throughout the total area of the rigid flex PCB and gives flexibility only where it is revealed– is not adequate. For PCB manufacturing reasons, the shift from flex to rigid is not at the very same point throughout all layers, so any kind of (potentially hidden) vias in the flex layer should go back into the inflexible location by a larger margin compared to may be noticeable. Where tracks sign up with round pads in the copper of the flex circuits layer, teardrops must constantly be used; the steady change from linear to round removes a possible tension point at the joint.
Use of copper on the flexible circuits layer or layers likewise contributes to the listing of ‘special rules’ and also imagining just what is happening when the flexible section is called into action will certainly reveal why.
A common error is to have excessive copper on the flexible circuits layer– huge aspects of steel foil bound to the polyimide will certainly hinder flexing. If continuous copper is required, after that an appropriate level of cross-hatching will be needed. For comparable reasons, tracks need to be directed perpendicularly to the bend line. All copper needs to be derived the initial aluminum foil as plating on the flexible circuits surface area has the tendency to generate crystalline metal that is too fragile to ensure long life.
A version on the rigid flex PCB formula is the application of stiffening to a portion of the flexible circuits layer. Effectively, this defines an area of the assembly that is stiff, but which does not bring components. Stiffeners could give support throughout assembly and can constrain the shape of the flexed circuits or they can offer framework and also minimum thickness where the flex circuits layer ends by going into an absolutely no insertion pressure connector. Although only offering mechanical assistance, the exact same collection of regulations puts on avoid creating problem aspects.
Those developing flexible PCBs have actually typically located worth in making paper versions of their boards– ‘paper dolls’. Today, 3D representation of the design can give that insight into real world geometry, while applying the parameters the rigid flex PCB manufacturer needs for high return. By attracting precise part accounts from its data source, engineers can be particular from the beginning that the bent as well as folded item will certainly fit together as meant, with no interference.