Alex: an Adom molecule LED nameplate

Alex's name, etched out of the soldermask over the ground plane, lit by 10 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 10 LEDs draw physically crosses the letters on its way back to the connector.

So the line you get to say to Alex, "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

Molecule compliance

Per molecule-design-guide and 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 160 x 64 mm, both exact multiples of 32 mm (the base scaffold's large-contact pitch), so it drops straight onto 6 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, 120 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

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

Fab notes

• Specify ENIG, not HASL. The letters are 113 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:

• 118 region polygons, bounding box 112.59 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 from a parametric tscircuit source. One command per name:

scripts/make-nameplate.sh "Alex"

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.