Applying DFM Analysis to Flexible PCBs

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The use of flexible printed circuit boards (PCBs), whether stand-alone or to connect rigid boards, has rapidly grown over the past decade. This growth has been driven by the proliferation of smaller form factors of products, such as wearable electronic devices. Because of their unique properties, flex circuits require special manufacturing methods as compared to rigid PCBs and can be less tolerant of issues that negatively affect manufacturability.

This article describes design-for-manufacturing (DFM) methods for flex circuits to help identify and correct problems during design. Applying these DFM techniques can save costs and ensure the project stays on schedule.

Flex circuit designs have unique properties and materials that separate them from rigid printed circuit boards. The flex circuits’ thinness makes them more delicate, and they are more susceptible to accidental damage during manufacturing. This 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 and methods. These various materials present a challenge for manufacturing. When combined with typical FR-4 PCB materials, the complexity increases. The greatest challenge is posed by differences in the thermal expansion characteristics of the various materials. These characteristics need to be addressed in DFM reviews.

Designs that have both rigid and flexible circuitry contain all circuit construction elements; separate rigid circuits are connected by flex circuits to form a single assembly, eliminating 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.

To read this entire article, which appeared in the September 2021 issue of Design007 Magazine, click here.


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