Traceability Marking: 2D Codes, Serialisation and Read Rate

A board that carries a serial number and a two dimensional code can be traced from the panel it was cut from to the customer that received it. The marking is a small part of the cost and the enabler of everything else in a traceability system.

What the Mark Carries

A two dimensional code can carry a lot number, a serial number, a date code or a reference to a database record. The choice between embedding the data and referencing it determines how the system behaves when the relationship changes.

Embedding the data makes the mark self contained, which is useful where the reader has no network access. Referencing a database keeps the mark small and allows the data to be updated, at the cost of depending on the database being available.

The practical arrangement for most products is a short unique identifier in the mark and everything else in the database. The mark then stays the same size as the data set grows.

Symbology and Size

A data matrix code is the usual choice for a small area because it can be read at a low contrast and its size scales with the amount of data. A QR code carries more data and is more familiar, and it requires more area.

The module size must be large enough for the reader and the marking process. A code that is readable by a laboratory scanner may be unreadable on the production line at speed.

The quiet zone around the code is part of the code. A mark surrounded by copper or by a legend that encroaches on the quiet zone will read intermittently. Our fabrication notes describe where the mark is placed relative to the other features.

Marking Methods

Laser marking removes or alters the soldermask to expose the material beneath, producing a high contrast mark. It is fast and permanent, and the parameters must be controlled so that the laser does not damage the copper or the laminate underneath.

Inkjet printing applies a legend ink that must cure and adhere. It is gentler and it produces a lower contrast mark, and the ink must survive cleaning and any coating process.

Labels are applied as a separate part and are the easiest to change, at the cost of an adhesive that must survive the environment and a label that can be removed or transferred. Our coating notes describe how a label interacts with a coating process.

Read Rate and Verification

The read rate is the proportion of codes that a reader decodes on the first attempt. It should be measured on the production line with the production reader, because a code that reads in the laboratory may not read under the lighting of the workstation.

The causes of a poor read rate are a module size that is too small, insufficient contrast, damage from handling and a quiet zone that has been encroached upon.

The grade of the mark can be assessed against an industry standard, which scores the contrast, the modulation, the axial non uniformity and other parameters. Grading is useful where two sites must agree on what is acceptable. Our quality notes describe the inspection of the mark with the other features.

Serialisation and Data Management

Serialisation means that every unit carries a unique identifier, which requires the marking process to draw from a controlled sequence and to record what was marked.

The sequence must not repeat and must not skip in a way that breaks the relationship between the records and the physical units. A duplicate identifier is worse than a missing one because it corrupts the trace of two units at once.

The records should link the identifier to the panel, the assembly lot, the test result and the shipping record so that a single lookup reconstructs the history. Our industrial assembly notes describe the data structure used for control equipment.

Where the Mark Is Placed

The mark must be visible after assembly, which means it cannot be covered by a component, a connector, a label or a coating that is opaque to the reader.

Where the board will be broken out of a panel, the mark must survive the separation and remain in a position that is accessible on the finished unit. A mark near the breakaway tab is at risk from the stresses of depaneling.

The placement should also consider the reader’s geometry: a mark on a surface that is always facing a wall in the installed product cannot be read during service. Our design release checklist notes where this requirement is recorded.

Verification in Production

Every unit should be scanned and the read confirmed as part of the process, rather than the marking being checked on a sample. The scan is the moment at which the mark enters the traceability system.

A unit whose mark does not read is either reworked or scrapped, and the record of that decision should be kept. Allowing an unreadable unit to continue breaks the chain that the whole system exists to provide.

The rework of a mark, whether by re-lasering or by applying a label, must preserve the identifier rather than assigning a new one. Assigning a new one severs the link to the earlier records and creates a unit with two histories.

Additional Considerations for This Build

Practical attention to 2D code pays for itself here, because it decides whether the finished board behaves as the drawing intended. Where the requirement is not stated on the fabrication drawing or in the assembly notes, the shop has to assume a default, and that default is rarely the value the design was simulated with. Stating 2D code explicitly, together with the tolerance that applies, removes the assumption and keeps the result predictable from batch to batch.

Process Control and Verification

On a design of this kind, read rate is the item that decides how the rest of the board is arranged. Where a value sits close to a process limit, the drawing should say so, since the shop can then open the process window rather than working to a nominal figure that carries no tolerance. A stack-up that is drawn rather than described removes most of the ambiguity from a quotation, and it lets the fabricator price the board against the dielectric and copper weights that will actually be used.

Where the requirement is not written down, the shop supplies its own default, and the default is chosen for the process rather than for the design. The measurements that matter are the repeatable ones: conductor width and spacing, annular ring, finished hole size, plating thickness and surface finish are all verifiable on a coupon that travels with the panel.

FAQ

How much data can a small code hold? Enough for a unique identifier of a dozen or so characters in a few millimetres, which is more than most traceability systems need.

Does laser marking damage the board? At controlled parameters it marks the mask and does not reach the copper. Parameters that are too aggressive expose copper and can create a short.

What does gopcb provide for traceability marking? We provide mark placement and sizing recommendations, laser or inkjet parameters verified for read rate on the production reader, code grading where required, and records linking each identifier to the panel, the lot and the test result.