Electronic Ring FPC Layout Notes
Required final geometry
- Board type: flexible FPC for an electronic ring
- Board outline: strict rectangle, 72.26 mm × 5.5 mm
- Board thickness target: 0.15 mm flexible FPC
- Rolled ring inner diameter: 19 mm
- Rolled ring midline diameter: 23 mm
- Midline circumference check: π × 23 mm = 72.26 mm, matching the required developed length
Layout intent
- Route traces along the longitudinal centerline wherever practical.
- Keep components centered across the 5.5 mm width and symmetric about the board midline.
- Space components evenly along the 72.26 mm length to support bending into a round ring.
- Reserve functional zones along the strip:
- Left end / one side: magnetic charging/contact pads
- Left-center: LED light area
- Center: main controller / MCU area
- Right-center: small LiPo battery area
- Opposite end / return side: secondary magnetic/contact or test/contact area as needed
Mechanical / FPC constraints
- Use 0.15 mm total FPC thickness as the fabrication target.
- Avoid placing tall or rigid components directly in high-flex regions where possible.
- Keep the FPC rectangular with square corners unless later manufacturing constraints require rounding.
- Maintain copper and component clearances from the board edge for manufacturability.
Current execution note
The board outline has been configured to 72.26 mm × 5.5 mm with a 2-layer layout setup, 0.15 mm board edge inset/keepout, and a 0.15 mm target FPC thickness captured in project metadata. Existing component footprint area is larger than the available strip area, so the placement pass prioritizes centered, symmetric, even spacing and reports any remaining manufacturability issues through DRC.
Layout rules applied
- Board outline: 72.26 mm × 5.5 mm rectangle
- Board inset / keepout: 0.15 mm
- Minimum trace width target for dense FPC routing: 0.075 mm
- Placement strategy: both layers allowed for compact low-height components; functional zones reserved for MCU, LiPo/power, LEDs, and magnetic contacts
Verification result
- Verified board setup after resizing: 72.26 mm length, approximately 5.5–6.0 mm displayed width depending on baked layout rounding, rectangular outline, 2 copper layers.
- Density check: current design has 32 components with approximately 676 mm² total footprint area versus approximately 434 mm² board area.
- Result: existing component set cannot physically fit inside the required 72.26 mm × 5.5 mm strip. Automated placement recommended at least 83 mm × 7 mm, but this was not applied because it would violate the required ring circumference and strip width.
- DRC check: active airwire errors remain because the board is not routable in the required mechanical envelope with the current component set.
Required next design action
To meet the strict 72.26 mm × 5.5 mm FPC requirement, reduce or replace the current footprint set with true ring-scale parts: chip-scale/WLCSP MCU or smaller module-free MCU, bare LED die or 0402 LED, very small magnetic pads, and a physically compatible micro LiPo/contact arrangement. The current larger footprints must be reduced before a clean centered/symmetric/routable layout can be achieved.