Rigid-Flex Printed circuit board Design: Advantages and Design Recommendations. This article will discuss what rigid-flex PCBs are, the benefits of utilizing them, and also the rules for designing with them for an application. In electronics, we sometimes come across seemingly new technologies that have roots in the past. Rigid-flex Printed circuit board technologies trace back somewhere around Half a century to the need to replace wiring harnesses in spacecraft. The initial commercially available mobile computer (which weighed a little over 25 pounds!) used rigid flex pcb design technologies. Today, notebooks, wearable technologies, medical devices, test equipment, and satellites are some of the applications that count on rigid-flex PCBs.
Exactly what is a Rigid-Flex PCB? With a rigid-flex PCB, flexible circuit substrates and rigid circuit substrates are laminated together. Rigid-flex PCBs cross the boundaries of traditional rigid PCBs as well as the unique properties of flex circuits designed to use high-ductility electrodeposited or rolled annealed copper conductors photo-etched onto a flexible type of insulating film. Flex circuits include stackups made from an adaptable polyimide like Kapton or Norton and copper laminated together through heat, acrylic adhesive, and pressure.
Similar to conventional PCBs, it is possible to mount components for both sides of the rigid board. Because of the integration that occurs between rigid and flex circuits, a rigid-flex design fails to use connectors or connecting cables between the sections. Instead, the flex circuits electrically connect the system together. Lacking connectors and connecting cables accomplishes a number of things:
Enhances the ability from the circuit to transmit signals without loss
Accommodates controlled impedance
Eliminates connection problems including cold joints
Frees space for other components – Every rigid-flex PCB is divided into zones which feature different materials and varying layer counts. Rigid zones could have more layers than flexible zones, and materials shift from FR-4 to polyimide in transition zones. Complex designs often transition from rigid to flex and to rigid several times. Since these intersections occur, the overlap of rigid-flex materials requires keeping holes out of the transition zone to keep up integrity. In addition, many rigid-flex designs include stainless steel or aluminum stiffeners that offer additional support for connectors and components.
Different Design Rules Pertain to Rigid-Flex PCB Design – Different challenges cancel out the versatility and adaptability that allow you to build three-dimensional designs and products. Traditional flex pcb china PCB designs allowed you to definitely mount components, connectors, and also the chassis to your product towards the physically stronger rigid part of the assembly. Again, with regards to traditional designs, the flexible circuit only served as an interconnect while decreasing the mass and boosting the resistance to vibration.
New product designs along with improved flex circuit technologies have introduced new design rules for rigid-flex PCBs. Your design team has the freedom to put components on the flexible circuit area. Combining this freedom using a multilayer approach to rigid-flex design allows you and your team to develop more circuitry into the design. However, gaining this freedom adds several challenges with regards to routing and holes.
Flexible circuits always have bend lines affecting routing. As a result of possibility of material stress, you are unable to place components or vias near the bend line. And even when components are properly located, bending flex circuits places repeated mechanical stresses on surface-mount pads and thru holes. Your team can reduce those stresses by utilizing through-hole koqcyp and through bolstering pad support with a lot more coverlay to anchor the pads. When you design your trace routing, follow practices that reduce stress on your circuits. Use hatched polygons to keep flexibility when carrying a power or ground plane on your own flex circuit. You need to use curved traces instead of 90° or 45° angles and utilize teardrop patterns to modify trace widths.
Teardrop patterns as used for trace-to-trace connections. These practices decrease stress points and weak spots. Another best practice distributes stress across traces by staggering the best and bottom traces for prototype pcb assembly. Offsetting the traces prevents the traces from laying over one another in the same direction and strengthens the PCB. You should also route traces perpendicular towards the bend line to reduce stress. When moving from rigid to flex and back to rigid, the number of layers from a single medium to the other may differ. You may use trace routing to incorporate stiffness towards the flex circuit by offsetting the routing for adjacent layers.1,2,5,6.