Issue link: https://iconnect007.uberflip.com/i/1276973
96 DESIGN007 MAGAZINE I AUGUST 2020 It is common practice to include the materi- als stackup in the fabrication notes, and we also encourage designers to use the IPC mate- rials slash sheets when calling out materials. The overall thickness is important in rigid board design but takes on even more signifi- cance with flex and rigid-flex design. IPC-2223 provides guidelines for minimum bend radius. Again, your fabricator is another excellent resource when there are concerns about flex- ibility. Once your fabricator understands how the circuit is designed for end-use, they can offer insights based on their years of experi- ence. One tip to improve flexibility is to use "un-bonded" layers to reduce the overall thick- ness. This simple adjustment significantly improves flexibility and prevents the dreaded "flex that doesn't flex" experience. Another recommendation may be using crosshatch shielding rather than solid cop- per shielding. This is often a balance of elec- trical and mechanical requirements, and the crosshatch pattern is highly customizable. For example, if solid copper shielding is required, but there are concerns in the bend area, the crosshatch pattern can be created in just the bend area, leaving areas that are not flexing as a solid copper shield. Removing more or less copper in those regions or layers has a signifi- cant impact on flexibility. These are just a few of the ways that your flexible circuit fabricator can provide guidance and suggestions to improve the flexibility of the circuit in end-use. Communicating those requirements in the data package and working with your fabricator during the design process is simple and can have a significant impact on the successful outcome of the design. While I don't really think that flexible circuit design is black magic, I do think there are tips and tricks that, learned over time, can greatly affect the perfor- mance of flexible circuits in end-use. FLEX007 Tara Dunn is the president of Omni PCB, a manufacturer's rep firm specializing in the PCB industry. To read past columns or contact Dunn, click here. to be included in the assembly drawings, but those drawings rarely get passed along to the bare board fabricator. Most often, although the flexible circuit is intended for three dimen- sions, the data files and information the fab- ricator receives is two-dimensional. Including the end-use requirements in the data package, and then taking the extra step of asking your fabricator to review the design for any recom- mendations to improve flexibility and reliabil- ity, is a simple combination that can yield great benefits. Who better than the fabricator, build- ing flexible materials day in and out, to provide recommendations on product performance? There are many subtle ways to improve flexibility and reliability. From a fabrication standpoint, the way parts are oriented on the production panel can improve flexibility. The rolled annealed copper on flexible laminates has a grain direction; orienting the circuit so that the bend areas are aligned with the grain direction can impact flexibility. Another fab- rication tool used to improve flexibility is the decision to button or pattern plate. Some fabri- cators elect to use a panel plating process as a default, while others choose button plating as their standard. When panel plating, the entire panel is plating with electrodeposited copper. This electrodeposited copper is not as flexible as rolled annealed copper on the flexible lami- nates. Button plating, on the other hand, plates only the pads and through-holes, leaving the circuitry to be formed on the rolled annealed copper. If this is a concern, adding a note to the fab drawing will ensure the button plating process is used. Who better than the fabricator, building flexible materials day in and out, to provide recommendations on product performance?