Whether you are designing the latest pace-maker or a LED strip, you have definitely pondered awhile about rigid PCBs and flex PCBs. You might have gone through a pile of literature, called up friends who have already done it (after all flex PCBs have been around for more than half a century now), and deliberated with your team to finally settle on a rigid-flex PCB. Well, what had started as a cutting-edge requirement to enable humanity's space dreams is today almost ubiquitous - think smart, wearable devices. There are many reasons why rigid-flex has become common, and the reasons are based on practical requirements of the time: dense designs, ever-decreasing size of devices, signal integrity requirements, and so on. But all these (size, density, etc) require a flex design, which increases the cost; and you want a balance - you go for rigid-flex. In the shortest possible way, quoting an earlier blog (not reinventing the wheel), here is the 'why' of choosing rigid-flex: "For nearly all applications, customers continue to demand smaller, lighter, and more cost-effective products. Competitive pressures also force designers to bring these new products to market at an ever-increasing rate. Designers can deploy flexible PCB materials (flex/rigid-flex) to meet challenging form-factor requirements, eliminate connectors, and improve performance. "
But as soon as a solution becomes popular, we start looking at enhancements to make it even better and optimize it further. Even in the rigid-flex PCB world, we have come a long way. To again quote from an earlier blog, Making Rigid-Flex PCB Design a Little Easier, "Designers once integrated the flexible portion of their circuitry as a connector from one rigid board to another. But now that there are even more stringent area demands, designers are now placing components on the flexible circuit area." Along with the new possibilities, applications, and requirements comes the part where we at Cadence can contribute - enabling you as designers in the most cost-effective and productive way possible.
So how does PCB Editor enable you to design a rigid-flex PCB? Well, in many ways! But I am listing a few of the more important ones here.
Rigid-Flex Transformation (Bending)
Not only do you have the bend area capability on the 2D workspace, but you can also transform your rigid-flex designs from a flat 2D state into a transformed 3D state. You can visualize how your designs will look like when they are in their intended state. Oh, and the centering feature of 3D Canvas automatically recenters rigid-flex designs on the canvas after a bend operation.
Multiple flex laminates supporting flex circuit coverlays
The soldermask layer in rigid PCBs is no good for flex PCBs. You now need a flex circuit coverlay. So, Cross Section Editor supports the entry of non-conductor layers - mask and coating layers used in rigid, flex or rigid-flex applications. You will usually add these layers above the Top or below the Bottom surfaces but can also add them within the core stackup to accommodate multiple independent flex laminates. The Cross Section Editor provides total thicknesses for each stackup in terms of accumulated conductor layers as well as an option with mask layer thicknesses included.
The multi-cross section support is complemented by an option to output a multi stackup table. The table supports entries for all conductor and non-conductor layers, material, and thicknesses.
And, yes, the surface finish options have been enhanced too. So you can choose the right finish from the options available.
Zone management for rigid and flex
Now that you have a design that is a mix of rigid and flexible parts, you need a capability to manage the physical areas pertaining to these.
A physical zone is used to map an area of the design to one of the stackups created in the Cross Section Editor. Zones can be rigid or flex areas consisting of varying layers. Rigid zones, for example, might be comprised of 10 conductor layers and soldermask whereas a flex zone may contain 2 conductor layers plus several mask layers such as coverlay, adhesive, or stiffeners.
Zones automatically include associated keepouts and optional constraint regions and rooms. Any part of the board that is outside of any zone will use the Primary Stack-up for its layer cross-section.
Checking Coverage and Clearances - Interlayer Checks
When you are designing a rigid PCB, you verify the proper clearance and coverage for masks and surfaces. Rigid-flex designs not only have the same mask and surface finish requirements but the addition of bend areas, stiffeners, and so on, that require special clearances or overlaps of materials, spacing, and design features. So you need (and get) the interlayer checks capabilities. What's more, you get the power of in-design checks, as mentioned by Ed Hickey in the white paper Automating Inter-Layer In-Design Checks in Rigid-Flex PCBs: "By allowing you to perform DRCs for various non-electrical flex layers, the tool (PCB Editor) helps to save time and avoid respins. The tool also supports real-time concurrent team design, so multiple PCB designers can work on the same PCB design database. "
Conclusion
So far so good but words are only words, why not try it out? Walk the walk? Click here for a Rapid Adoption Kit with detailed step-by-step procedures on the Rigid-Flex functionality, including various important aspects not discussed in this blog, such as IPC-2581 Layer Function support, multi stack up grid, and manufacturing preparation support. The Rapid Action Kit is accompanied by a database that you can use to perform the exercises in the document.
Note: The above link can only be accessed by Cadence customers who have a valid login ID for https://support.cadence.com