Traceability marking answers one question: given any single board, can you determine which lot it came from, which process steps it passed, and which material batches it used. That is a different job from component legend. A designator tells the line where a part goes; a unique board ID tells quality which board this is. The first serves assembly readability, the second serves quality investigation and field analysis. Define them separately in review, give each its own board real estate, and make sure neither is overwritten or profiled away.
The first design decision is the marking keep-out. A board ID needs a fixed area that will not be hidden by components, connectors, heatsinks, shields, or labels. Consider whether it must still be readable after assembly, whether it is read from the top or bottom side, and whether profiling and panel separation can damage the area. Call the keep-out out on the mechanical or assembly drawing rather than dropping a box on the legend layer. When board area is genuinely tight, treat board-ID readability as a layout constraint during review instead of squeezing it in at the end.
The second decision is the carrier. A board ID can be human-readable characters, a machine-readable code, or both. Each form places different demands on surface condition, contrast, the layer it lives on, and tolerance to downstream processing. Documentation should state the chosen form, the content structure (for example whether it carries part number, revision, lot, and sequence), who supplies the numbering rule, whether it must correspond to panel position, and whether the fabricator may generate sequence numbers. This draft specifies no character height, code type, module size, contrast, or marking process. Those come from the customer specification and engineering confirmation, and missing items should be listed as open.
The third decision is the data chain. The mark itself is only an index; its value comes from what it can be linked to, such as material lot, process step, inspection result, and rework history. Project documents should state the required granularity (lot or individual board), who retains the records, in what form, whether a traceability list ships with the goods, and how the customer raises a traceability request in the field. Do not commit to a granularity or retention period without a written agreement. Confirming marking definition, numbering rule, record scope, and delivery form during review avoids a board change after production starts.
Related reading: align traceability and record scope on the quality and inspection page, confirm the relationship between the marking area and the profile on the PCB tolerance page, and check that the marking layer ships complete using the Gerber file preparation checklist. Submit a confirmed definition through the online quote page. Verify links and locale routes before publication.
FAQ
Can the unique board ID share a layer with component designators?
Technically yes, but the intent differs. Designators serve assembly identification and the board ID serves the traceability index. Define location, content, and readability separately, and mark the board-ID keep-out on the drawing so components, labels, or profiling do not compromise it.
Should the board ID be human-readable or a 2D code?
It depends on the reading scenario, available area, downstream processing, and customer specification. This draft gives no default and specifies no character height or code type. Agree the form, content structure, and reading method during review.
Is traceability required at lot level or per board?
That is a project parameter to agree in writing beforehand. Finer granularity increases marking, record, and handoff requirements. Do not assume per-board traceability without agreement.
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Unique board ID keep-out area and traceability marking defined on a PCB mechanical drawing