skill

Adom Footprint Standard: 300um Solder-Ball Layer

Public Unreviewed

by John Lauer

Every Adom footprint carries a hidden User layer of 300um jet-paste ball positions

footprintstandardsolder-pasteessemtecinstapcb
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skill / adom-solder-ball-layer-standard
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Contents

Adom Footprint Standard: 300um Solder-Ball (Jet-Paste) Layer

Every Adom-owned footprint must carry a dedicated, hidden-by-default layer marking where the 300um solder-paste balls land when assembled on the Essemtec solder-paste JET dispenser.

The rule

  • Add a dedicated User layer to every footprint - proposed User.9 named Adom.SolderBalls (independent of F.Paste, so stencil paste and jet-deposit positions never conflict).
  • On that layer, place the 300um (Ø0.30mm) dot positions at 0.25mm pitch — a slight, intentional overlap between adjacent balls (0.30mm balls at 0.25mm centers). The overlap is correct; do not spread the balls apart to "fix" it. adom-footprint/src/paste.rs currently implements DOT_DIA=0.30, DOT_PITCH=0.45, MARGIN=0.06 — the 0.45mm pitch is wrong and must be updated to 0.25mm.
  • The layer is HIDDEN BY DEFAULT in every viewer (it is assembly/process data, not for normal review). FpView already exposes a "paste dots" toggle, off by default - keep that behavior.
  • Through-hole pads (machine pins etc.) get a ring of 300um dots around the annular pad (they have no F.Paste aperture today, so paste.rs yields zero dots for them - this must be extended).

Why persist it (vs compute on the fly)

Today paste.rs computes the dots ephemerally (SVG overlay only, SMD pads only). Making it a persisted layer in the .kicad_mod means: the jet-dispense program is reproducible and reviewable, it travels with the footprint into KiCad/Fusion/Altium, and the assembly team sees exactly where paste lands - hidden until they turn it on.

The paste itself (material spec)

The paste run through the jet dispenser is leaded — never assume a lead-free (SAC) alloy for Adom paste work unless explicitly told otherwise.

Property Value
Alloy composition 63Sn / 37Pb (leaded, eutectic tin-lead, melts ~183 C)
Flux Indium 12.8HF (the flux vehicle is the non-metal fraction — no separate flux step)
Powder mesh Type 6-SGS (fine powder; what makes 300um jetted balls feasible)
Metal content 80% by weight

Rendering Paste Elements (3D viewers)

  • Render each ball as a hemisphere (half sphere), flat face on the pad — not a full sphere.
  • Ø0.30mm at 0.25mm pitch: adjacent hemispheres overlap slightly by design.
  • Material/color: leaded solder — dull silver-gray, not bright lead-free silver.
  • 0.30mm is the default and the working minimum; do not go smaller without explicit direction.

Reconcile the dot diameter

The adom-footprint code uses 300um (DOT_DIA=0.30); the adom-footprint SKILL text says 250um. Standardize on 300um (per the dispenser spec) and fix the skill text.

Action for footprint owners (Drew, Arav, Ray)

  1. Extend adom-footprint/src/paste.rs to (a) EMIT the dots onto the Adom.SolderBalls User layer in the .kicad_mod (not only the SVG overlay), and (b) handle through-hole pads (annular ring).
  2. Update DOT_PITCH in adom-footprint/src/paste.rs from 0.45 to 0.25 (see "The rule").
  3. Backfill the layer into existing Adom footprints (a batch pass over the libraries).
  4. Keep it hidden by default in FpView / all viewers.

Reference implementation of the through-hole ring + 300um hemispheres in a 3D viewer: the Adom machine-pin pages (this work).