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72 DESIGN007 MAGAZINE I JULY 2019 board outline and stackup modifications nec- essary when the shape of the board changes. With flex stackups, there are additional materi- als and layer types to model, such as cover lay- ers, stiffeners, and adhesives. These materials are intelligent and are understood at design ver- ification as well as the hand-off to manufactur- ing. Control of where bends occur is critical, so a bend area object defines the location, radius, angle, and origin. Attributes also define place- ment, routing (e.g., via utilization, trace cor- ners, trace width changes, etc.) and plane metal (e.g., hatch/cross-hatch) rules in the area. For place and route, each rigid-flex area has its own external/internal layers, so parts can be placed on any external layer (including flex re- gions and/or in cavities) with appropriate pads and openings automatically handled. During routing, true arcs are utilized to minimize stress fractures in flex regions, and they adhere to the constraint-driven, correct-by-design methodol - ogy for which we're known. Curved teardrops are automatically generated and maintained dynamically. Due to the automation through- out layout, design changes are easy and safe. Regarding 3D design and MCAD collabora- tion, the complexity of rigid-flex structures re- quires full 3D design and verification, not just 3D viewing. For example, parts can be placed on bent or flat surfaces in 3D. Also, 3D DRC checks will identify any interference when the circuit is bent. An enclosure can be imported from MCAD and mated with the design to vi- sualize and check alignment. In addition, rig- id-flex structures (and their bend attributes) can be passed to MCAD for further modeling and analysis. With signal/power integrity analysis, as trac- es transfer between flex and rigid areas, their impedance and propagation speed changes. Our analysis tools accurately model distinct stackup areas to accurately model this effect. They also recognize the unique material types, such as adhesives, copper foils, and stiffeners. And for manufacturability verification and hand-off, DFM is critical to successful fabri- cation of rigid-flex. An extensive set of flex/ rigid-flex DFM checks is available during de- sign. A few examples include conductors par- allel to bend area, plated holes too close to a stiffener, and rigid area copper close to inter- face area. Valor technology is integrated di- rectly within Xpedition's layout editor to en- able checks at any time during design with er- Figure 2: Today's enterprise-level EDA tools are often designed for flex and rigid-flex circuits.

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