Flexible PCB Design Review

flux

I continued the cleanup around U4/U5.
What changed
  • Pushed the PN7160 block further into the upper-left and kept its clock/support parts tight:
    • U4 now around (-31.7, 21.2) mm
    • Y2 around (-30.3, 13.0) mm
    • C9/C10 around (-34.2, 16.2) mm and (-37.2, 16.2) mm
    • C8 around (-32.0, 26.0) mm
  • Pushed the STM32 block further to the right:
    • U5 now around (33.5, 2.2) mm
  • Kept the edge interfaces in place:
    • J1/J2 along the bottom area
    • J3 on the left side
Result
  • The center routing corridor is more open now.
  • Component spacing is still comfortable on the card; the board remains low density and all parts still fit easily on the top side.
  • The card outline and 2-layer setup remain unchanged.
What did not clear yet
The remaining problems are still the same category:
  • overlapping copper around U4 and U5
  • many unrouted airwires
So this confirms the blocker is not mainly placement anymore. It’s now mostly:
  1. footprint/copper geometry around U4/U5, and/or
  2. unrouted traces in that hotspot region.
Thickness status
Your planned card thickness is still preserved as the manufacturing target:
  • intended flex build remains documented as:
    • 50 µm PI core
    • 18 µm copper/side
    • 25 µm coverlay/side
    • 0.2 mm local FR4 stiffeners only where needed
  • and the final 0.70–0.76 mm laminated card thickness is still the target for fab/lamination, not the live Flux rigid stackup model.
Best next step
The next pass should be routing/copper cleanup, not more placement:
  1. inspect U4 and U5 footprint copper directly
  2. route these first through the opened corridor:
    • I2C_SCL
    • I2C_SDA
    • NRST
    • crystal nets around Y2/C9/C10
    • PN7160 control nets
  3. then re-run PCB checks
If you want, I can next give you a U4/U5 hotspot routing checklist with the exact nets to route first and what to inspect on each footprint.
Give routing checklist
Check footprint copper
Run DRC review
List critical nets

Placed components

5:16

Placed 14 component(s): R2, R5, U5, C9, C8, R3, J3, J2, C10, J1, R4, Y2, U4, C6

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U5 PB6 - U4 2C_SCL/SPI_SCK
U4 VDD(TX) - U4 TVDD_IN
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Omni-Touch NFC Biometric Smart Card thumbnail
NFC-harvested Omni-Touch wearable board with PN7160 frontend, STM32L041 host MCU, SE050 secure element, palm-grid matrix interface, fingerprint UART connector, and status LED on a flex smart-card form factor.

Properties

Pricing & Availability

Distributor

Qty 1

Arrow

$9.76–$11.04

Digi-Key

$15.28–$16.29

LCSC

$21.40

Mouser

$18.02

TME

$0.00

Verical

$7.94–$13.20

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