# haptic\-harmony slim 9b21

## Description

=====================================================================
 HAPTICA HARMONY B1  \-  FLEXIBLE PCB FABRICATION & ASSEMBLY SPEC
 Gestura AI LLC  \|  4\-layer rigid\-flex \(flex \+ selective stiffeners\)
 IPC\-6013 Class 3  \|  ENEPIG finish
=====================================================================

1\. BOARD SUMMARY
   \- Flat outline 27\.0 x 9\.2 mm\. Origin at center: X = \-13\.5\.\.\+13\.5, Y = \-4\.6\.\.\+4\.6\.
   \- 5 rigid \(stiffened\) facets in series along X, joined by 4 flexible fold/bend zones\.
   \- Folds into a finger ring \(US 7\-13\); same PCB for all sizes, only the battery changes\.
   \- Build & electrically test FLAT, then fold into the ring and two\-shot overmold\.

2\. FACET / STIFFENER MAP  \(X\-span mm \| width \| stiffener \| key parts\)
   S1 Power     \-13\.50\.\.\-10\.20 \| 3\.30 \| YES \| U3 MCP73831, U4 LC05111, U5 TPS7A0233, D1; C1\-C5,C29,C32; R21,R22,R\_STAT
   Fold 1       \-10\.20\.\.\-9\.20  \| 1\.00 \| NO  \| bend hinge
   S2 RF         \-9\.20\.\.\-3\.50  \| 5\.70 \| YES \| U1 nRF54L15 \(WLCSP\-47, 0\.30mm pitch\), Y1 32MHz, Y2 32\.768kHz, L1, FB1; C6\-C11; TP1\-TP9
   Fold 2        \-3\.50\.\.\-2\.50  \| 1\.00 \| NO  \| bend hinge
   S3 Antenna    \-2\.50\.\.\+2\.76  \| 5\.26 \| YES \| ANT1 Johanson 2450AT42E010; L2\-L4 / C12\-C14 pi\-match
   Fold 3        \+2\.76\.\.\+3\.76  \| 1\.00 \| NO  \| bend hinge
   S4 IMU\-Touch  \+3\.76\.\.\+7\.55  \| 3\.79 \| YES \| U2 BMI270, U6 IQS7222A; C15\-C19,C30,C31; R3,R4,R5,R14,R16\-R20
   Fold 4        \+7\.55\.\.\+8\.55  \| 1\.00 \| NO  \| bend hinge
   S5 Haptic     \+8\.55\.\.\+13\.50 \| 4\.95 \| YES \| U7 BOS1921, PZ1 piezo, L5; C20\-C28; R1,R2,R7,R15
   Total = 27\.00 mm\.  ALL component pads land on a stiffened facet; NO components/pads in any fold\.
   \(S4/S5 widths reflect the U6\<\-\>U7 stiffener rebalance: each IC sits \~0\.045 mm inside its stiffener;
    U7 pads are on\-board and on\-stiffener\.\)

3\. LAYER STACKUP  \(4\-layer flex, HDI 1\+2\+1\)
   L1 Top    : signal \+ ALL ICs \(\+ some passives\)
   L2 In1\.Cu : GND plane \+ ANT1 solid GND pour
   L3 In2\.Cu : GND / signal
   L4 Bottom : signal \+ passives
   \- Core: adhesiveless polyimide \(e\.g\. DuPont Pyralux AP or equivalent\)\.
   \- Copper: 18 um \(1/2 oz\) rolled\-annealed \(RA\), inner & outer \(RA for flex durability\)\.
   \- Coverlay \(polyimide\) over flex regions; LPI soldermask on rigid facets ONLY\.
   \- HDI: laser microvias L1\<\-\>L2 \(and L3\<\-\>L4\) for U1 nRF54L15 WLCSP\-47 \(0\.30mm pitch\) escape;
     buried/core vias L2\<\-\>L3 \(1\+2\+1\)\. Via\-in\-pad \(filled\+capped\) under the WLCSP\. NO through\-hole vias in WLCSP field\.

4\. IMPEDANCE / RF
   \- 50 ohm single\-ended controlled impedance on the RF trace \(U1 \-\> pi\-match \-\> ANT1\), referenced to In1 GND\.
   \- Keep RF trace short, no stubs; pi\-match \(L2\-L4 / C12\-C14\) tunable for VNA S11\.

5\. FOLD / BEND ZONES  \(the 4 flex hinges \- what lets the board bend as designed\)
   \- 4 zones, each 1\.0 mm wide \(Fold 1\-4 at the facet boundaries\)\. Each:
       \* NO stiffener \(must flex\)      \* NO vias \(via keepout = 0\.0 mm, enforced\)
       \* NO components                 \* NO LPI soldermask \-\- polyimide coverlay only
   \- Bend radius: strip wraps into the ring \(bore \~18\.2 mm \-\> \~9\.1 mm neutral\-axis radius\)\.
     Min static bend radius \>= 6x flex thickness \(\~0\.2 mm \-\> \>=1\.2 mm\); the \~9 mm ring radius is well within limits\.
   \- Copper across hinges: route PERPENDICULAR to bend axis \(across fold, along Y\); NO 90\-deg corners
     \(arced/teardrop transitions\); STAGGER top/bottom traces; HATCHED \(not solid\) ground in bends
     to reduce stiffness & cracking\. Minimize conductors crossing each hinge\.

6\. GROUNDING
   \- Solid GND planes on In1 \+ In2\. GND stitching vias around RF and between planes,
     placed ONLY on stiffened facets, NEVER in fold zones\.
   \- ANT1: solid GND pour on In1 as RF reference, with the ground keep\-out under/around the radiator
     per the Johanson 2450AT42E010 datasheet \(no copper under the antenna\)\. \[TODO: exact keep\-out dims\.\]
   \- Crystals Y1/Y2: local ground guard ring \+ ground under the parts; short, guarded oscillator traces\.

7\. STIFFENER MATERIAL & BONDING
   \- Stiffener under each rigid facet \(S1\-S5\): FR4 0\.20\-0\.30 mm \(or polyimide stiffener\) bonded to the
     BACK \(L4 side\) of the flex\.
   \- Bonding adhesive: thermoset acrylic/epoxy bonding film \(e\.g\. DuPont Pyralux bond\-ply or equiv\.\) or a
     qualified PSA, applied ONLY under rigid facets \-\- NEVER across a fold zone\.
   \- Stiffener edges set back \~0\.1\-0\.2 mm from each fold so the hinge stays fully flexible\.

8\. PLACEMENT & ASSEMBLY
   \- ALL ICs on TOP side only \-\> single\-sided reflow \-\> avoids double\-reflow flex delamination\.
     Passives may be on BOTTOM\.
   \- Assemble \+ reflow FLAT; electrically test FLAT \(SWD bring\-up, RF S11, sleep current\) BEFORE folding\.
   \- Component bonding for ring reliability \(flex \+ curvature stress\):
       \* Epoxy UNDERFILL on U1 WLCSP\-47\.
       \* Corner\-bond / edge\-stake the large QFNs \(U6 IQS7222A, U7 BOS1921\); secure tall/edge parts\.
       \* Actuator \+ battery bonded per the enclosure \(mechanical\) spec\.
   \- Fold sequence: wrap the strip at the 4 hinges into the ring polygon AFTER assembly/test; then two\-shot overmold\.

9\. SURFACE FINISH / CLASS / DFM
   \- Finish: ENEPIG \(fine\-pitch WLCSP \+ solder reliability\)\. Build to IPC\-6013 Class 3\.
   \- Min trace/space per Class 3 \+ WLCSP escape \(\~75/75 um in escape, relaxed elsewhere \-\- confirm with fab\)\.

10\. KNOWN ITEMS / OPEN
   \- Y2 \(32\.768 kHz LFXO, ECS\-\.327\-6\-34QCS\-TR, ECX\-34Q\): vendor 2\-pad footprint VERIFIED correct
     \(two 1\.1 x 1\.9 mm pads, 2\.5 mm pitch; matches 3\.2 x 1\.5 mm datasheet\)\. The single Flux
     "Overlapping Copper" DRC is a spurious schematic\-symbol contact \(phantom 3rd pin on a 2\-pad part\);
     NOT in the footprint/Gerbers; does NOT affect fabrication\. NO part swap required\.
   \- Facet boundary outlines \(S1\-S5\) are 0\.15 mm dashed rectangles currently on the Top layer \(reference geometry\)\.
     For clean fab, move them to a documentation/silkscreen layer \(not copper\) and add per\-facet silkscreen
     labels \(S1 Power \.\.\. S5 Haptic\)\. S1's outline is present and identical to S2\-S5\.
   \- Remaining DRC = 163 airwires = unrouted nets \(routing is the next phase\), not defects\.
=====================================================================

## Project Details

- **Owner:** gestura
- **Created:** 9/19/2026
- **Last Updated:** 9/19/2026
- **Visibility:** Public

*The full schematic, PCB layout, bill of materials, and interactive design are available at [https://flux\.ai/gestura/haptic\-harmony\-slim\-9b21\~yl](https://flux.ai/gestura/haptic-harmony-slim-9b21~yl).*

---

*Generated from [https://flux\.ai/gestura/haptic\-harmony\-slim\-9b21\~yl](https://flux.ai/gestura/haptic-harmony-slim-9b21~yl)*