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78 DESIGN007 MAGAZINE I JUNE 2023 • Vendor experience: Does your vendor have experience with rigid-flex and flex? Rigidized flex: An Alternative Solution A lower cost alternative to a rigid-flex is a rigidized flex. is is a flex circuit (double- sided or multilayer) that uses a rigid stiffener in place of the PCB portion of the rigid-flex. When you place components on a flex circuit you need to stiffen the area where components will be placed. is stiffened area will assist with SMT placement (prevent flex movement during placement) and prevent solder crack- ing of the solder joints. We also use stiffeners with through-hole components. We can use all kinds of materials to create a stiffened area: FR-4, aluminum (heat displace- ment), machined stainless steel (flatness), ceramic, and additional layers of polyimide. When do we use a rigidized flex? Honestly, a rigidized flex is common when you need to place components on a flex. How- ever, as a customer considering a rigid-flex, is it possible to put all your components on one side of the flex? If you can, then make a mul- tilayer flex, and add a stiffener. You get all the benefits of a rigid-flex with a lot less cost. Designers of products are learning the advan- tages of rigid-flex: • Denser PCB packaging: e elimination of interconnect giving the PCB designer more maneuverability and room. PCB real estate has become expensive because there are more components on the boards. • Denser system packaging: is forces designers into 3D solutions. Rigid-flex is the perfect solution because there's more stuff in the package. • Simplified assembly: is means improved reliability, and one-piece instal- lation vs. connectors, cables, and/or addi- tional flex jumpers. is all equals an over- all lower cost of manufacturing. • Leveraging materials: e ability to lever- age materials from both a PCB and a flex circuit in one integrated package allows for high speed and signal integrity solutions, as well as shielding characteristics. Possible Disadvantages of Rigid-flex Rigid-flex is a great solution for the right application. But with good, there is always something else to consider. So, what are the potential "gotchas" with rigid-flex? • Cost: Average rigid-flex cost will be about 20–50% higher than a PCB and 20–30% higher than flex. • Volumes: If there is high volume, the cost curve can flatten. But for North American manufacturing and volumes, the differ- ences in price between a PCB and a rigid- flex can be dramatic. • Manufacturability: Sometimes this is tough. It's based on number of layers and types of materials chosen. Figure 2. Figure 3: a) Rigidized 3-layer black Kapton with FR-4 stiffener; b) Rigidized 3-layer with FR-4 stiffener. a b

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