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4.2 Marking Methods & Materials

Laser, labels, inkjet—durability, contrast, and compatibility with finishes/coatings.

Marks are the IDs that turn a bare board into a traceable product, and the right choice keeps them readable from oven to audit. Laser etches, high-temp labels, and inkjet legend each bring different stamina through reflow, cleaning, and coatings, but they all succeed only with good contrast and smart placement. Finishes and conformal coat add constraints—great marks live on solder mask or rails, not on pads—so artwork reserves clean windows instead of inviting lift or smearing. Fast scans demand quiet zones, consistent corners, and data that matches what MES (Manufacturing Execution System) expects. Get those ingredients aligned and a simple 2D code becomes living genealogy, tying every unit to materials, processes, and tests without slowing the line.

4.2.1 What a “mark” must survive (and prove)

Every unit ID or 2D code has to (1) stay readable after reflow, cleaning, and handling; (2) scan fast on the line; and (3) match what MES expects so genealogy stays intact. That means picking the right method and where it lands, plus defining the data it encodes in your label/traceability spec and MES route.

4.2.2 Methods compared (pick the right tool)

Method

What it is

Durability through reflow/clean

Contrast & readability

Finish/coating compatibility

Typical uses

Laser (direct part marking, DPM)

Ablates/etches solder mask or FR-4 to create text/2D codes.

Excellent (nothing to melt); survives solvents.

Best on matte, high-contrast mask; keep a clean mask window.

No impact on finishes—mark on mask, not on pads. Plays well under/over coat when kept in clear zones.

Unit SN/2D on PCB, panel marks, post-assembly branding.

High-temp labels (polyimide + thermal transfer ink)

Printed, pressure-sensitive labels rated for reflow.

Very good if spec’d for lead-free temps; choose adhesives rated for your profile and cleaners.

Excellent with dark text on light label; scanner-friendly if quiet zone preserved.

Place on mask or rails; avoid solderable finishes/pads. Confirm your clean/coat sequence; some labels are coat-through, others need a mask window.

Unit SN, MAC/IMEI, panel ID; shipping/pack labels.

Inkjet on board (legend printer)

Direct ink onto mask (like silkscreen but printed).

Good when surface prep is right; protect from aggressive cleaners.

Needs clean, matte mask for crisp edges; avoid pads/metal.

Keep off solderable finishes; plan coating so text stays legible.

Supplemental text, small 1D/2D where laser/labels aren’t preferred.

Golden rule: never put marks on pads or finishes—keep legend/ink/labels off solderable copper and VIPPO caps; use dedicated mask windows or rails.

4.2.3 Contrast & placement (so scanners don’t hunt)

  • Contrast first: matte mask boosts edge contrast for both laser and ink/legend; choose mask/legend colors that read under your AOI/test lighting as well as hand scanners.
  • Use the rails: reserve space on panel rails for the big, line-of-travel barcodes/2D codes; keep board-level unit codes in a consistent corner.
  • Keepouts: don’t straddle V-score/tab lines; leave quiet zones around codes so verifiers grade cleanly (tie to panel drawing).
  • Off the copper: marks and labels live on mask/FR-4, not on solderable areas or test pads. (Your DFM notes should already say this.)

4.2.4 Finish & coating interactions (avoid surprises)

  • Finishes: ENIG/ImmAg/ImmSn are fine under/near labels if you don’t cover the pad; OSP areas oxidize—keep marks and labels off active copper, period. (OSP still okay elsewhere on the board.)
  • Cleaning & coat: plan surface prep so ink/labels stick, and define whether labels are under or over conformal coat. If over, spec label materials that tolerate your chemistry; if under, add a mask window so the coat edge doesn’t creep under the label.

4.2.5 When to mark (process timing)

  • Pre-reflow labels: common for unit SN on top side—only if label is reflow-rated; verify readability after AOI and cleaning.
  • Post-reflow laser: ideal for permanent IDs without adhesive risk; add a short scan gate in MES right after marking.
  • Pack-out labels: shipping/customer labels printed at the last station—tie their data to the unit/panel scans so genealogy stays intact. (Encode BOM rev if your customer requires it.)

4.2.6 Data & verification (what the system expects)

  • Put the data fields and formats (e.g., which 1D/2D symbologies, what goes into each) in the Labeling & Traceability spec in your Golden Data Pack.
  • Add scan points to the MES route (print→verify→apply; laser→verify), and block WIP if a code fails decode. That’s how you avoid “shadow spreadsheets.”
  • Keep sample images of good/poor marks in the pack so line leads train operators quickly.

4.2.7 Designer/ME checklist (print this with your fab pack)

  • Chosen marking method per location: laser vs high-temp label vs inkjet legend.
  • Artwork shows dedicated zones on panel rails and on the PCB; no marks on pads/finishes.
  • Contrast ensured: matte mask where marks live; readable legend fonts.
  • Coating plan clear: label under/over coat with proper windows/materials.
  • Label/traceability spec lists data fields, symbologies, BOM-rev policy, and scan points in MES.



Bottom line: Mark on mask/rails with the method that fits your heat and chemicals, design for contrast and keepouts, and wire every mark into MES scans so IDs become genealogy—not just ink. Do that, and your codes survive ovens and solvents, and your data survives audits and RMAs.    


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