Are you considering using a rigid flex PCB for an application? If so, the initial and most apparent solution to the inquiry ‘why?’ is making use of the flexibility and also to allow activity between two traditional boards– even if the motion is limited to providing resonance resistance.
Flex circuits that really flex in regular usage can, however, be considered a special case; very usually, the intent is to give a reliable interconnect in between 2 boards that do not depend on the very same plane. In such instances, the flexible component may only flex throughout final assembly of the item as well as never do so once more.
Rigid flex PCB can be viewed as an alternate interconnect strategy or as cable substitute. One flexible circuits area replaces, at a minimum, a wire plus 2 connectors– which could be worthwhile for costs of materials factors– and releases the quantity the adapters would have inhabited. This is substantial for such products as wearables, where every mm3 within the enclosure is made use of, and in systems where two or even more PCBs need to be folded right into area in last assembly. PCB suppliers report that items where room as well as weight go to a costs are amongst the fastest growing adopters of rigid flex PCB innovation
Other benefits include: enhanced integrity, with less connectors and connected solder joints; and control of the signal course in between the wiring on the boards at either end of the flex.
Today, the design procedure is aided by 3D capable PCB design software; if you are aiming to make optimal usage of area, you should make certain there is no interference in between element profiles. Increasingly, design software program can likewise model the flexed state of the non stiff component to develop parameters such as bend span– and do so dynamically, to inspect the entire path of system in which both inflexible aspects relocate, in typical usage.
Mature innovation.
Rigid flex PCB fabrication is a fully grown modern technology, with well developed policies for success. The first is to develop and also preserve a discussion with the rigid flex PCB manufacturer and also to make sure that any type of alterations to design rules or design checks (DRC) are imported into the layout plan in use and also abided by.
A number of the standards for an effective outcome of a rigid flex PCB design circulation from the residential properties of the products being employed. The base material for the stiff section is probably to be FR4, while the flex is typically a polyimide movie (typically called Kapton, after DuPont’s product) with copper aluminum foil applied as well as a coverlay film imposed in place of the solder mask.
Some thought is needed regarding how the product buildings match the job and this swiftly shows where care ought to be taken. The copper-to-film bond is a junction in between different materials; the tighter the bend radius, the better the tensions at the border and the greater the danger of delamination. The tracks, although slim, are copper and if the bend span is too tiny, repeated flexing carries the risk of stress crack.
The shift between rigid as well as flex PCB is additionally an important aspect; as with cable television termination, flexing forces should not be enforced at the transition as this can create very small bend distance over a tiny distance. Again, dynamic modelling of folding in 3D is helpful and also the structure of the layer rigid flex PCB stack-up is essential for reliability as well as manufacturability.
Several usual mistakes can be stayed clear of by attention to a couple of key points in the design process. One aspect is the requirement for a larger copper ring around any type of opening drilled in the flex and, as a relevant point, the have to leave a larger splitting up between drill hole/pad and also surrounding tracks. The flexible circuits movie is just that and also the impact of that adaptability is to increase regular (inevitable) resistances. For that reason, if a drilled opening misses concentricity with its pad by a tiny margin, the hole will certainly still plate as well as connectivity with the by means of will certainly be untouched– yet there is a risk of a brief to a track passing too close.
Reducing vias in the flex circuits area is preferable by itself; the expense of vias is above in the stiff, thinking the design needs a dual sided flex circuits. This is one aspect where the setup of the rigid flex PCB stack-up that comprises the complete PCB is vital. The manufacturing procedure is in part subtractive– there will be layers over and also under the flex in fabrication that are eliminated uniquely to release the flex circuits sector before the process is full. The stack-up ought to be configured to make sure the polyimide layer is completely sustained through any type of exploration. Thinking of a drill bit attempting to pass through a thin, deformable film will right away reveal why.
Change
Simply taking vias in the flexible location back right into the inflexible section– the flex layer runs throughout the total location of the rigid flex PCB and provides adaptability only where it is subjected– is not sufficient. For PCB manufacturing factors, the change from flex to rigid is not at the same factor throughout all layers, so any (potentially buried) vias in the flex layer have to step back into the rigid area by a larger margin than could be apparent. Where tracks join circular pads in the copper of the flex circuits layer, drops should always be used; the progressive shift from linear to round gets rid of a possible stress point at the joint.
Use of copper on the flexible circuits layer or layers likewise adds to the checklist of ‘unique policies’ and also imagining what is taking place when the flexible sector is called into action will show why.
A common error is to have way too much copper on the flexible circuits layer– big locations of steel aluminum foil bound to the polyimide will certainly inhibit flexing. If continuous copper is required, after that a proper degree of cross-hatching will certainly be called for. For comparable factors, tracks must be transmitted perpendicularly to the bend line. All copper must be derived the initial foil as plating on the flexible circuits surface area has the tendency to produce crystalline steel that is too fragile to assure long life.
A variant on the rigid flex PCB formula is the application of stiffening to a portion of the flexible circuits layer. In effect, this marks an area of the assembly that is inflexible, yet which does not lug elements. Stiffeners can offer support during assembly and can constrict the form of the flexed circuits or they could provide framework and also minimum thickness where the flex circuits layer terminates by getting in an absolutely no insertion force port. Although just giving mechanical assistance, the very same collection of regulations puts on prevent producing issue locations.
Those designing flexible PCBs have actually commonly discovered value in making paper models of their boards– ‘paper dolls’. Today, 3D depiction of the design can give that idea right into real world geometry, while using the specifications the rigid flex PCB manufacturer requires for high return. By drawing exact element accounts from its database, designers can be particular from the outset that the flexed as well as folded item will mesh as intended, with no disturbance.