Rigid Flex PCB Design Rules Guaranteeing Reliable Products (1)

Breakthroughs in fabrication have actually translated right into new design constraints and standards.

For several years flex and rigid flex PCB commonly turned up in products as a flexible cable television between 2 rigid boards. The past five to seven years have actually brought tighter space constraints and miniaturization challenges. Developers should currently put parts on the flexible circuit, using it like a rigid substrate. Utilizing both the rigid and the flexible areas for components, while feasible, presents new design restrictions that call for more advanced PCB design methods.

To prevent fracturing or unnecessary stress on parts, prevent putting elements and vias at the bend locations. A typical, well-known rule is that routing must be orthogonal to the bend line to minimize material stress at the bend. Routing on the following layer with the bend location should be offset to stay clear of the I-beam result. Traces that do not follow this policy could accidentally add rigidity to an area that is planned to be flexible. In addition, the area where rigid and flex zones come together may need overlap of material and require unique spacing for holes and conductive materials. It is handy to consider the transition area a stress-relief area. it shows a four-layer rigid board attached to a two-layer flex PCB, which on its opposite connects to another four-layer rigid board.

Rigid and flex PCB frequently use different materials, and the rigid section generally has even more layers than the flex section. Many advanced makers could sustain these designs with more than two flex layers. To ensure flex circuits with added layers work well in all problems, stiffeners that bring rigidity to these PCBs are placed near components or port locations or on the contrary side. Stiffeners are made from materials such as stainless-steel or aluminum, with the enhancement of dielectric material like a polyimide build-up. Smaller units often call for the flexible section to be curved or folded up.

The PCB cross-section editor for a solitary stack-up must now support numerous cross-sections standing for the different PCB laminates. In addition to supporting conductor, plane and dielectric layers, cross-section editors have to include new mask and finishing layers above and below the surface areas of the flex PCB, such as:.

Electroless nickel electroless palladium immersion gold (ENEPIG) for unique plating areas.
Stiffeners– aluminum or stainless steel– that limit bending where parts are placed, to stay clear of splitting or peeling off.
Material masks that consist of (valuable) steels, adhesives and solder paste masks.
A coverlay (cover layer), which is an adhesive-coated film pushed into the stack-up to shield the circuit.
Developments in fabrication have reached materials and the variety of added mask/conductive layers for flex and rigid flex PCB. New materials– conductive/nonconductive layers, and surface area coatings– need developers to by hand examine if the design components on the flex circuit are meeting the maker’s design standards. This includes a substantial quantity of time to the design phase.

To stay clear of manual checks and guarantee the design is developed appropriately, designers need in-design inter-layer checks to flag issues as they are developed. Checking at the PCB manufacturing sign-off stage is too late in the design cycle to discover errors, and makes the design process unpredictable. Real-time capability can stay clear of taxing actions later on at the same time.