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74 DESIGN007 MAGAZINE I SEPTEMBER 2021 they are more susceptible to accidental dam- age during manufacturing. is negatively affects the yield, increasing the per-item cost. Let us explore why running concurrent DFM is even more important with flexible circuitry than for rigid PCBs. Flexible circuits are typically built using a combination of material types (Table 1) and methods (Figure 2). ese various materials present a challenge for manufacturing. When combined with typical FR-4 PCB materials, the complexity increases. e greatest challenge is posed by differences in the thermal expansion characteristics of the various materials. ese characteristics need to be addressed in DFM reviews. Designs that have both rigid and flexible circuitry contain all circuit construction ele- ments; separate rigid circuits are connected by flex circuits to form a single assembly, eliminat- ing the possibility of mating and signal routing errors. While rigid-flex can be more costly, in actuality, they may be more cost-effective and increase yield with a reduction of touch steps during assembly. 10 DFM Challenges for Flex and Rigid-Flex Flex circuits and the interface between rigid and flex segments can have problems that do not exist with standard rigid PCBs. e follow- ing are 10 potential problems and how to solve them proactively. Table 1: Common construction methods for flexible circuits. Figure 2: Flex circuitry can be constructed with or without adhesives. Adhesive-less circuits are used in applications needing higher performance, while those using adhesives are often used for low-layer count applications. Figure 3: Techniques to provide support for surface mounting of components on the flex circuit.