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10 FLEX007 MAGAZINE I APRIL 2019 Feature by Todd MacFadden BOSE CORPORATION Like most kids, I spent my childhood dream- ing that someday when I grew up I would get to optimize the design and manufacturability of flexible printed circuits. I envisioned the fantastical circuit outlines that would look like a squashed tarantula in 2D, but would origami intricately and elegantly into impossibly small 3D spaces. And, like other kids, I imagined the rigorous training I would receive in school and on the job to teach me exactly what materi- als to select and what parameters to use to achieve magnificent, robust bends that would (obviously) conform generously to IPC bend radius guidelines. OK, not really. As a child, I dreamed of being a famous musician, until I learned more about the supply and demand curves for mediocrity. And, as many of us who have done this know, there is no formal training and often no right answer or perfect solution for FPC design. The IPC design standards—such as IPC-2223: Sectional Design Standard for Flexible/Rigid- Flexible Printed Circuits and IPC-6013: Quali- fication and Performance Specification for Flexible/Rigid-Flexible Printed Boards—pro- vide indispensable guidance and are justifi- ably the go-to starting place. But the authors of these standards are careful to distinguish between requirements and guidelines, and they acknowledge that the standards cannot possibly encompass all use cases. This is increasingly true as miniaturization requirements force us to pack more functional- ity into ever-smaller packages, and it becomes more difficult to conform to IPC construction recommendations. Achieving robust FPCs requires frequent, iterative interaction inter- nally among the mechanical, electrical, and PCB design teams, as well as with the fabrica- tors and assemblers. The sooner in the design cycle we can engage the supplier and assem- bler, the better. This article will present three case studies of early prototype designs that didn't go so well, and the lessons learned from each to highlight

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