Issue link: https://iconnect007.uberflip.com/i/1073397
JANUARY 2019 I FLEX007 MAGAZINE 13 comes the physical space constraints. The ini- tial board shape and concept of component placement is derived at first from mechanical CAD (MCAD)—usually as a DXF/DWG file— which only supplies a two-dimensional outline of the overall flattened board shape (Figure 2a and b). MCAD has been used by many to plan the flex by using "sheet metal" modeling. This allows the mechanical engineer to design the overall board substrate shape to a single thickness in a folded state, which is then flat - tened to provide the 2D panel outline of the rigid-flex board. This allows the designer to place and route the rigid-flex board in 2D PCB design software. It's an acceptable method, but suffers the following significant flaws: • The PCB designer still must use paper doll mockups to check in-situ folding and component placement, which is a time- consuming—and usually frustrating— process • When changes are needed, the iteration must always begin in the MCAD tool flow with a re-export of board outlines, and an import into PCB CAD with the associated component and routing moves taking much longer • The PCB designer has very little immediate visual feedback regarding component placement or folding—it has to rely entirely on the designer's imagination; while we know PCB designers have an excellent imagination, they are still human (enough said) Oddly enough, many flex PCB fabrica- tors still urge designers to make a paper doll mockup (Figure 3) of the flex boards from a 1:1 assembly drawing print-out cut out with scissors and folded into the target installation Figure 2a and b: Sheet metal in MCAD works okay, but is not ideal. Figure 3: Paper dolls are still recommended by flex fabricators, but are not optimal.