Are you thinking of using a rigid flex PCB for an application? If so, the initial as well as most apparent answer to the concern ‘why?’ is to make usage of the adaptability and also to allow movement between two standard boards– even if the activity is restricted to giving vibration resistance.
Flex circuits that actually flex in regular use can, nevertheless, be considered a special case; extremely frequently, the intent is to give a reliable interconnect between 2 boards that do not lie in the very same airplane. In such situations, the flexible part might only flex during final assembly of the item as well as never ever do so again.
Rigid flex PCB can be viewed as an alternate interconnect strategy or as wire substitute. One flexible circuits section replaces, at a minimum, a cable plus 2 ports– which might be worthwhile for costs of materials reasons– and releases the volume the ports would have inhabited. This is substantial for such items as wearables, where every mm3 within the enclosure is used, and also in systems where two or more PCBs should be folded into location in last assembly. PCB makers report that items in which area and also weight go to a premium are amongst the fastest growing adopters of rigid flex PCB modern technology
Other advantages include: enhanced reliability, with less adapters and also connected solder joints; and also control of the signal path in between the circuitry on the boards at either end of the flex.
Today, the design process is assisted by 3D capable PCB design software application; if you are trying to make optimal use of room, you need to make sure there is no interference in between element accounts. Increasingly, design software program could also model the flexed state of the non stiff part to develop criteria such as bend radius– and also do so dynamically, to inspect the entire course of system where the two rigid elements move, in typical usage.
Fully grown technology.
Rigid flex PCB fabrication is a mature innovation, with well established policies for success. The very first is to establish and preserve a dialogue with the rigid flex PCB manufacturer and to guarantee that any adjustments to design regulations or design checks (DRC) are imported right into the layout bundle being used as well as stuck to.
Many of the guidelines for a successful outcome of a rigid flex PCB design flow from the homes of the materials being utilized. The base product for the stiff portion is most likely to be FR4, while the flex is generally a polyimide film (typically called Kapton, after DuPont’s material) with copper foil used and a coverlay film enforced in place of the solder mask.
Some idea is needed with exactly how the product homes match the task as well as this swiftly shows where treatment should be taken. The copper-to-film bond is a junction in between dissimilar products; the tighter the bend radius, the greater the anxieties at the limit and the higher the threat of delamination. The tracks, although slim, are copper as well as if the bend distance is as well tiny, repeated flexing brings the risk of anxiety crack.
The change between stiff and flex circuits is likewise an important aspect; just like cord discontinuation, flexing forces ought to not be imposed at the shift as this could produce quite tiny bend distance over a tiny range. Again, vibrant modelling of folding in 3D is useful and the composition of the layer rigid flex PCB stack-up is crucial for reliability and also manufacturability.
Numerous common errors can be avoided by attention to a couple of key points in the design process. One location is the requirement for a larger copper ring around any opening pierced in the flex and also, as an associated point, the need to leave a larger separation between drill hole/pad and adjacent tracks. The flexible circuits film is simply that as well as the impact of that adaptability is to increase typical (unavoidable) resistances. As a result, if a drilled opening misses out on concentricity with its pad by a tiny margin, the hole will certainly still plate and connectivity through the through will certainly be unaffected– yet there is a risk of a brief to a track passing too close.
Minimising vias in the flex PCB circuits region is preferable by itself; the cost of vias is greater than in the inflexible, assuming the design requires a double sided flex circuits. This is one area where the setup of the rigid flex PCB stack-up that composes the complete PCB is essential. The manufacturing process is in component subtractive– there will be layers over as well as under the flex in fabrication that are removed precisely to launch the flex circuits section prior to the process is full. The stack-up must be set up to make sure the polyimide layer is fully sustained with any kind of boring. Thinking of a drill little bit attempting to penetrate a slim, deformable movie will right away show why.
Shift
Simply taking vias in the flexible area back right into the inflexible part– the flex layer runs throughout the total area of the rigid flex PCB and also offers adaptability just where it is exposed– is not sufficient. For PCB manufacturing reasons, the change from flex to inflexible is not at the same point throughout all layers, so any kind of (potentially hidden) vias in the flex layer should go back into the stiff aspect by a bigger margin than might be obvious. Where tracks sign up with round pads in the copper of the flex circuits layer, teardrops must constantly be used; the progressive transition from direct to circular removes a possible tension point at the joint.
Use of copper on the flexible circuits layer or layers also contributes to the listing of ‘unique guidelines’ and visualising just what is occurring when the flexible sector is called into action will certainly show why.
An usual mistake is to have excessive copper on the flexible circuits layer– huge aspects of steel foil bound to the polyimide will hinder flexing. If constant copper is required, then a suitable level of cross-hatching will be called for. For comparable factors, tracks must be directed perpendicularly to the bend line. All copper should be obtained the initial foil as plating on the flexible circuits surface area has the tendency to generate crystalline metal that is as well fragile to guarantee long life.
A version on the rigid flex PCB formula is the application of tensing to a portion of the flexible circuits layer. Essentially, this delineates an area of the assembly that is inflexible, yet which does not carry parts. Stiffeners could supply assistance during assembly and could constrain the form of the flexed circuits or they can offer framework as well as minimum thickness where the flex circuits layer terminates by going into a zero insertion pressure adapter. Although only providing mechanical assistance, the same set of rules applies to stay clear of developing problem aspects.
Those creating flexible PCBs have frequently discovered value in making paper designs of their boards– ‘paper dolls’. Today, 3D representation of the design could supply that insight right into real world geometry, while using the specifications the Rigid Flex PCB manufacturer requires for high yield. By attracting precise component accounts from its data source, engineers can be specific from the outset that the flexed as well as folded product will certainly fit together as planned, with no disturbance.