Flex PCBs
Flex PCBs work very differently. Instead of the woven fiberglass substrate, they use extremely thin (often under 3.9 mils / 0.1
mm) flexible plastic films (made of polyimide or polyester) as the base layer.
Real thicknesses of substrate layers
Rather than sheets of copper foil, rolled annealed copper is bonded directly to the flexible plastic substrate using an adhesive.
Rolled annealed copper
This allows the copper to bend and flex with the plastic film substrate underneath.
Additional layers can be added by building up more plastic film and copper in an alternating stack.
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Rigid Flex Design Guide
