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86 DESIGN007 MAGAZINE I OCTOBER 2019 Interview by Andy Shaughnessy FLEX007 Andy Shaughnessy speaks with Guest Edi- tor Kelly Dack about the current state of flexi- ble circuit design and manufacturing. As a PCB designer working for an EMS provider in the Pacific Northwest, Kelly shares some thoughts about what he sees in the flex and rigid-flex circuit segments, and the challenges and op- portunities that flex designers face. He also points out the need for flex designers to have a thorough understanding of the final products that they're dealing with. Andy Shaughnessy: Kelly, can you start by talking about some of the interesting things that you see with flex? Then, we can discuss some of the chal - lenges as well. Kelly Dack: Work- ing for an EMS provider as a de- signer, I see a va- riety of ways that flexible cir- cuits are being designed into products. Only a decade ago, flex was considered too expensive and too hard to work with, and flex had lim- ited producibility. But now, the flex market is exploding, and flexible circuits are going into a vast array of products from micro-flex struc- tures utilized in hearing aids to products that require flex applications and serve as heaters and substitutes for cable harnessing. I spent some time at PCB West in Santa Clara last month, searching for flex companies that spe- cialize in flex-to-metal laminations for use as a specialized heat sink. I found out that there are many methods of attachment and lamination of different types of flex materials to metal, FR- 4, and other laminates. Shaughnessy: Tell us about that. Flex-to-met- al lamination sounds interesting, but it also sounds like a problem to laminate. Is this what you would call rigid-flex? Dack: Yes, stock thicknesses of sheet metal are being used more and more as a stiffener as well, due to its thermal conductive properties as a heat sink. We have customers who are combining their need for thermal transfer and ri- gidity as part of the equation for their rigid-flex solution. Shaughnessy: Is this with metal that would also flex? Dack: Well, it depends. It can be flexible, but thicker metal is not typically utilized in dynamic flexing applica- tions. Thicker copper foils or thin sheet metal stock laminated to a portion of the flex materi- al would work-harden and crack in a dynamic bending or rolling application. However, add- ed sheet metal stock or heavy copper can be "flexed" or bent for a single installation appli- FLEX DESIGN: Know Your Applications

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