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Rev B1 ECN-11 — NFC antenna on top side (draft)

Draft — EverTag Station only

Relocate the ST25DV04K NFC coil antenna to the top copper (component side) on Connectivity Module PCBs (232200–232204). Not approved. Observed on A3 boards; fix targets the B1 Altium release. Does not apply to Tag (230220) — Tag has a separate coil layout.

Ships in the same B1 respin as Rev B1 ECN-01 — GPIO remap.

What changes

The Station NFC tap zone is on the front face, center of the Connectivity Module enclosure (Quick Start — NFC tap zone). On A3 boards the 2-layer PCB coil is routed primarily on the bottom side (L4), opposite the PAN611 module and most SMT components on L1 (top).

A3 (current) B1 (proposed)
NFC coil placement Bottom side (L4) — away from PAN611 / enclosure front Top side (L1) — same side as PAN611 and ST25DV04K
Coil geometry 11 turns, 7.05 × 16.5 mm (shared with 230220 spec) Same target geometry unless layout forces minor shift
NFC function Works for commissioning Same — improved coupling to phone on front face

NFC works today on A3 — this is a layout optimization, not a functional bug fix. Moving the coil to the top side reduces the distance and dielectric stack between the antenna and the user's phone, which improves read/write reliability at the documented < 2 cm tap distance.

Rationale

Factor Bottom-side coil (A3) Top-side coil (B1)
Distance to phone PCB thickness (~1 mm FR4) + any component height + enclosure wall between coil and reader Coil faces enclosure front face directly — shortest path
Alignment with product UX User taps front of upper housing; coil radiates from opposite copper Coil on same PCB face as the enclosure NFC window region
ST25DV04K routing Longer feed from IC on L1 to coil on L4 Shorter AC1/AC0 feed — IC and coil on same side
Risk Lower (shipped, proven) Layout congestion on L1 — must not encroach PAN611 keep-out (ECN-03)

The nRF54 internal NFC peripheral is not used on any board — NFC is entirely via ST25DV04K + external coil (232200 §3.3 NFC). Firmware and I2C pin map are unchanged.

Scope

Item B1 change
232200–232204 Shared connectivity module layout — move NFC coil to L1 (top), paired inner layer per ST25DV04K 2-layer coil rules
ST25DV04K (IC + C8/C9/C10) May move with coil; re-tune matching caps after layout
Bottom layer (L4) Reroute traces previously sharing the NFC zone
232506 enclosure No mechanical change expected — confirm coil faces front tap zone in STEP
230220 Tag No change — separate coil layout (product families)

Gateway variants (232202/232203) and 232204 (radar) share the same base layout — verify NFC placement does not conflict with ESP32 ground fence, battery area, or A121 radar window after the move.

Altium implementation (after design approval)

  1. PCB orientation — Confirm in enclosure STEP which PCB face is front (NFC tap). The coil active area on L1 must face that inner wall.
  2. Coil redraw — Place the 2-layer coil on L1 + inner layer per ST25DV04K design guide (same turn count and dimensions as today unless ME/HW approve a shift). Do not mirror the 230220 Tag coil blindly — Station enclosure context differs.
  3. Keep-out — Stay outside PAN611 antenna zone (5.0 × 3.25 mm per ECN-03). Check clearance to ESP32 RF area on gateway variants.
  4. Feed traces — Short, symmetric AC1/AC0 from ST25DV04K to coil; no sharp corners under the coil span.
  5. Bottom layer cleanup — Move displaced L4 routing; preserve DFM (no new through-hole).
  6. Matching — Re-run ST25DV04K antenna tuning (C8, C9, C10) on first B1 prototype — values may shift with layer move.
  7. Gerber review — Confirm coil appears on Top Copper (and paired inner), not Bottom Copper, before EMS release.

Verification (HW / QA)

  • Gerber: NFC coil on L1 (top), not L4 (bottom)
  • Enclosure fit: coil region aligns with front-face tap zone in assembled STEP
  • NFC functional: phone read/write via CB Admin at ≤ 2 cm — compare A3 vs B1 if samples available
  • NFC I2C: ST25DV04K detected at boot (no E05)
  • PAN611 / ESP32 RF smoke test — no regression from relocated pours or traces
  • All variants 232200–232204 — same coil position (shared layout)

Open items

# Question Owner Status
1 Confirm front face ↔ L1 mapping in 232506 + PCB STEP ME + Altium Pending
2 Target NFC performance metric (e.g. max tap distance, CB Admin success rate) for A3 vs B1 sign-off HW + FW Pending
3 Does coil move affect 232204 radar window / A121 placement? Altium Pending
4 Final C8/C9/C10 values after B1 prototype tune HW Pending