# Jon Chung: an Adom molecule LED nameplate

Jon Chung's name, **etched out of the soldermask over the ground plane**, lit by
15 side-view LEDs that fire inward across the board, powered from any
USB-C phone charger, and mountable in a probing workcell by four large machine
pins on the 32 mm base-scaffold grid.

## The one idea

**The name is the ground plane.** A rectangular GND copper pour covers the top
layer, and the soldermask is opened in the shape of the letters so bare plated
copper shows through. There is deliberately **no second ground path** (no
bottom ground pour), so every milliamp those 15 LEDs draw physically
crosses the letters on its way back to the connector.

So the line you get to say to Jon Chung, *"your name is part of the electrical
path that lights up the LEDs"*, is a statement about the netlist, not a
slogan. It is enforced by construction: the ground pour is sized to swallow
every ground pad on the board, so ground is bonded by geometry and the
autorouter is never given the chance to route a shortcut around the letters.

## The board

| | |
|---|---|
| Board | 268 x 76 mm, 2 layer, 4 mm corner radius |
| Pin box | **256 x 64 mm** = 8 x 2 on the 32 mm grid |
| Name | 209.2 x 40 mm, Familjen Grotesk Bold |
| Mask openings | 478 letter polygons |
| GND plate | 261.6 x 69.6 mm, top layer |
| LEDs | 15 x Würth WL-SMSW `155060GS75300`, 515 nm side-view |
| Current | 180 mA @ 5 V (15 x 12 mA) |
| Parts / traces / vias | 40 / 63 / 35 |

### Molecule compliance

Per [molecule-design-guide](https://wiki.adom.inc/adom/molecule-design-guide)
and [base-scaffold-system](https://wiki.adom.inc/adom/base-scaffold-system):

- A **large machine pin at every corner** (3.6 mm body press-fit into a 3.45 mm
  plated hole, 0.15 mm diametral interference).
- The pin box is **256 x 64 mm**, both exact multiples of 32 mm (the base
  scaffold's large-contact pitch), so it drops straight onto 9 x 3
  contact positions of the 18 x 18 field across the 576 x 576 mm workspace.
- **Minimal wings:** the board stops 6 mm outside each corner pin. That is as
  tight as the pin allows: a 5.2 mm annular ring eats 2.6 mm of it, leaving
  3.4 mm of solid laminate, about 2x board thickness, which is what a press-fit
  needs so insertion force does not crack the edge out.
- Corner pins carry power, not just mechanics: **MP1/MP4 are GND, MP2/MP3 are
  +5 V**, so the plate can run off a workcell control panel instead of USB-C.
  The GND pins land inside the plate, which means the scaffold's ground return
  also passes through the name.

## Why side-view LEDs

A normal chip LED is a top-view emitter: it fires straight up, away from the
board, and the copper you are trying to light sees nothing. This board uses a
true **side-view** part. The die sits on its side behind a window in the long
face of the package, so the beam leaves *parallel* to the board about 0.5 mm
above the soldermask. Ringed around the edge facing inward, the light rakes
across the plate at a grazing angle and washes the exposed-copper letters
instead of escaping to the sky.

Worth knowing if you go sourcing: Kingbright's `APTR3216` family is
*reverse-mount* (it fires down through a hole in the PCB) and Broadcom's
`HSMx-C265` is bottom-entry. Both come back in a "right angle SMD LED" search
and neither does this job.

- 1.6 x 0.8 x 1.1 mm; 2 pads 0.6 x 0.8 mm on 1.4 mm pitch
- 515 nm peak / 525 nm dominant, 260 to 560 mcd @ 20 mA, 140 deg 2θ½
- VF 3.2 V typ; run here at 12 mA through 150 R

## Power

USB-C VBUS (5 V) -> 150 R -> LED (3.2 V) = 12 mA each, **180 mA total**, well
inside the 500 mA a charger gives an unnegotiated sink, so any phone brick
works. `R_CC1`/`R_CC2` are the mandatory Rd pulldowns. Without them on *both*
CC lines a USB-C source never enables VBUS at all and the board is dead.

Layer plan is inverted from the usual convention on purpose:

- **Top** = GND, one rectangular pour. The name is cut out of it.
- **Bottom** = +5 V plane.

Everything is placed on the **top side only** (the line does single-sided
pick-and-place), so each LED string runs LED -> 150 R -> a via down to the +5 V
plane, while the cathode bonds straight into the plate.

## BOM

| Ref | Qty | Part | Package |
|---|---:|---|---|
| D* | 15 | Würth WL-SMSW `155060GS75300` side-view green 515 nm | 0603 side-view |
| R1 to R15 | 15 | 150 R ±1 % `CR0402-FX-1500GLF` | 0402 |
| R_CC1/2 | 2 | 4.7 k ±1 % `CR0402-FX-4701GLF` | 0402 |
| C1 | 1 | 10 µF X5R `0603X106K100CT` | 0603 |
| C2 | 1 | 100 nF X7R `0402B104J160CT` | 0402 |
| J1 | 1 | `TYPE-C-31-M-12` USB-C (JLC C165948) | SMD + 4 plated anchors |
| MP1 to MP4 | 4 | `MachinePinLargeStandard` | 3.45 mm plated hole |

Passives are all Adom Basic Parts. The LED is Mouser/DigiKey (~$0.40).

## Fab notes

- **Specify ENIG, not HASL.** The letters are 209 x 40 mm of deliberately
  bare copper and are the entire point of the board. HASL leaves them lumpy,
  ENIG leaves them mirror flat.
- Dark soldermask maximises contrast against the exposed letters.
- The four 3.45 mm machine-pin holes are an **interference fit** and are meant
  to be undersized. Do not let a fab house "correct" them to a clearance fit.
- Tented/plugged vias: there are vias whose rings lap onto LED resistor pads.

## Verifying the mask opens

Do not trust the render. Read the gerber. `F_Mask.gbr` is negative polarity
(`%TF.FilePolarity,Negative*%`), so what is *drawn* is where mask is *removed*:

- **478 region polygons**, bounding box **209.18 x 40.00 mm**, the letters
- the plate rectangle **absent** from F_Mask (present would mean inverted)
- **zero** letter regions in `F_Paste.gbr`. The letters are decoration, not
  solder joints, and must never be stencilled

## Reproducing it

Built with [adom-tsci](https://wiki.adom.inc/adom/adom-tsci) from a parametric
tscircuit source. One command per name:

```bash
scripts/make-nameplate.sh "Jon Chung"
```

Board size, pin box, LED count and silkscreen are all derived from the name's
ink box, so a new name is a one-liner. The source bundle attached to this page
has everything.