Flex PCBs Explained
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List of Terms and Materials
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Rigid Section: The stiff and non-bendable portion of the PCB made from FR4 or similar material.
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Flexible Section: The bendable portion of the PCB made from polyimide or other flexible dielectric material.
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Flex Core: The core layer of the flexible section, typically a thin layer of polyimide with copper traces on either side.
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Coverlay: A protective layer applied to the outer surfaces of the PCB to protect the copper traces from scratches and
environmental factors.
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Stiffener: A thin piece of rigid material (FR4 or metal) added to the flexible section to provide additional support and
prevent excessive bending.
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Bend Radius: The minimum radius at which the flexible section can bend without damaging the copper traces or delami-
nating the layers.
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Hole-to-Flex Distance: The minimum distance between a via or plated through hole and the edge of the flexible section.
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Impedance Control: Designing the PCB to maintain a consistent electrical impedance for signal traces to minimize signal
reflections and ensure signal integrity.
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Bookbinding Construction: A technique used where layers of flex PCB are manufactured in progressively longer lengths
around the outside bend radius. Helps reduce damage from bending, but increases cost by 30% or more.
Additional Resources
For more information on rigid-flex PCB design, visit our resources hub.
