Mechanical considerations for flexible circuits -Static and Dynamic Optimization

1. Mechanical Considerations
of Flexible Circuits
Static and Dynamic Optimization
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2. Design Guidelines
Mechanical Considerations
 Static (One-time Bend)
o Rule of Thumb, Bend radius for flex to install is 10x the thickness of the
flex this can often be pushed to 5x.
o Can use stiffeners to create a natural folding configuration.
o Keep stress concentrators well away from bend areas.
o A soft adhesive system may “pucker” on the inside of a tight bend radius.
 Dynamic (Multiple Bend)
o Rule of Thumb, Bend radius for dynamic flex is 100x the flex thickness.
o Conductor thickness and width should remain constant in bending areas.
o Conductors should be staggered from layer to layer and not stacked on
top of each other to increase flexibility.
o Conductor thickness and width should remain constant in bending areas.
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3. Design Guidelines
Material Selection – Type of Copper
 Dynamic – Considerations that effect Flex Life
o Grain structure and grain size, RA Cu. grain structure is best compared to standard
ED grain structure for Dynamic applications.
o Copper surface roughness, smoother is better.
*Comparison of crystal structure – cross-sectional observation of Cu. foil crystals after annealed
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4. Design Guidelines
Material Selection – Type of Copper
 Dynamic – Considerations that effect Flex Life
*Crystal structure & high flexibility mechanism
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5. Design Guidelines
Engineering & Designing FPC
 Make the circuit robust to withstand Flexing
o Preferred practice
is to route conductors
perpendicular
to bend and fold
areas in a single metal
layer if possible.
Bending Zone
Not Recommended
Bending Zone
Preferred Routing
o
Eliminate copper plating on the conductors in the flexing area (dynamic region) by utilizing selective
(pads plating/button plating‐only) allowing the circuit to have increased flexibility.
o
Conductors should be staggered from layer to layer and not stacked on top of each other to increase
flexibility.
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