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4.2 Marking Methods & Materials

Marking methods transform bare boards into traceable products, bridging the physical and digital worlds of manufacturing. Whether etched with lasers, printed with high-temp labels, or deposited with inkjet, the durability and contrast of these identifiers decide if genealogy survives ovens, cleaners, and coatings. Placement is equally critical—marks on mask or rails endure, while those on pads or finishes invite failure. When tied cleanly into MES scans, a simple code evolves into a permanent passport, proving where a unit came from and what it has been through.

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.


Conclusion: Selecting the right marking method, placing it for durability, and integrating it into MES ensures every identifier remains both scannable and trustworthy. The payoff is fast genealogy retrieval, resilient IDs through process stress, and reliable evidence for audits and customer returns.   


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