Issue link: https://iconnect007.uberflip.com/i/1073397
14 FLEX007 MAGAZINE I JANUARY 2019 shape to verify the form and fit. Even with 3D modeling in your tools, if it makes you feel bet- ter, go ahead, but it won't give you component clearance checking. For that, you need your EDA tools to physically analyze the assembly. Planning Fabrication, Folds, and Installation This is the part where most designers have a fairly intuitive grasp of flex design. We are already thinking in three dimensions here— it's the impetus for the whole exercise. But because it's natural, it can lead to a false sense of security in one's own ability to mentally plan the shape of the board and how it will fold. Modeling in 3D CAD grants us confirmation of what we envision is manufacturable. Beyond that, it prevents many real manufacturing and assembly problems such as poor panel utili- zation, component interferences, flex interfer- ences, and difficult or impossible installation into the final product assembly. The major professional EDA tools can do this, so why not jump in and design your rigid- flex boards from the get-go in the 3D-foldable environment? This lets the designer visualize the folded assembly directly with placement and routing to reveal any mismatches between the mental image of what the design should be and the physical instantiation of it (Figure 4). This immediate visual feedback will instantly reveal problem areas and allow for fast iterative adjustment, directly alleviating: • In-situ component interferences • Impossible flex folds and bends (ever imagined a flex circuit only to find that the flattened panel was folded back onto itself?) • Insufficient or excessive flex circuit length (this is a problem frequently discovered during costly prototyping runs!) • Poorly-oriented outlines resulting in bad panel utilization • Slow iteration cycles (MCAD g ECAD g place/route g review g MCAD g ECAD) In short, the PCB designer has the power and freedom to model, check, and make all adjustments directly. Designing and model- ing in 3D from the ground up will also lead to better rigid-flex board outlines because the PCB designer can quickly explore alternatives. For example, using a sideways folded broad flex instead of a lengthways folded long-thin flex may reduce layer count while also saving panel space for multiple transversely rotated panel instances (Figure 5). Figure 5: 3D modeling of rigid-flex (left) leads to better panel utilization (right). Figure 4: Natively modelling the rigid-flex assembly in 3D for design and planning.