Assembly Traceability Data Structure and Retention

Traceability is a data structure rather than a mark. The mark identifies the unit, and the structure decides what can be asked of it afterwards, which is the part that determines whether a field problem can be narrowed to a day or to a year.

What the Identifier Has to Be

The identifier has to be unique, readable at every station and stable for the life of the product. A serial number that is unique within a batch and reused in the next is not unique, and it produces a record that cannot be split.

The identifier is normally a two dimensional code that carries the serial and the part number, and it is applied before the first process step that has to be recorded. Our board quality notes describe the marking side of that.

What Is Recorded at Each Station

Each station records the identifier, the time, the result and the parameters that were used. The parameters are the part that makes the record useful, because a result without them cannot be compared with another unit.

What to record is decided by asking what would be needed to investigate a failure. A station that records only pass or fail produces a record that says a unit passed on a machine. Our first pass yield notes describe how the data is aggregated.

The unit is linked to the material lots that went into it, and the linkage is created at the step where the material is consumed rather than afterwards. A linkage that is reconstructed from a batch record links a unit to a batch rather than to a lot.

The difference matters in a containment, because a batch can be a day and a lot can be a reel. A containment that covers a day of production rather than a reel is a commercial problem as well as a technical one.

The record is a sequence of events against an identifier, which is the structure that allows a query in either direction: what happened to this unit, and which units saw this condition.

A record that is stored as a summary per batch supports the first query and not the second, which is the query that a containment needs. Our floor zoning notes describe how the stations are arranged so that the reading is part of the work.

A rework is an event and it belongs in the sequence, with the station, the operator and the reason. A record that shows a unit passing a station twice without a reason is a record that cannot be interpreted.

The rework also changes what the unit is, which matters for the containment query. A reworked unit is a different population from one that was not.

The retention period is set by the customer and by the product, and the retrieval has to work for the whole period. A record that is retained on a system that cannot be searched has the value of no record.

The retrieval test is worth doing rather than assuming. Asking for a specific unit that was built a year ago is the only test that proves the structure works. Our cleanliness notes describe a related measurement that is also only useful if it is searchable.

Process Control and Verification

Documenting the assumption is part of the design work, and a short note on the drawing prevents a question that would otherwise arrive a day later and cost a day of schedule. The process window is set by the narrowest step in the flow, so an improvement anywhere else shows up as margin rather than as yield until that step is addressed.

A short note on the drawing about handling, storage or packaging is often worth more than an extra decimal place on a tolerance. 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.

Is a date code enough for traceability? It narrows a containment to a date and not to a reel or a machine.

Does every station need to read the code? Every station that consumes material or changes the unit does, and the reading is part of the operation rather than an extra step.

What does gopcb provide for traceability? We provide a unique identifier readable at every station, parameters recorded alongside the result, material and lot linked at the point of use, a query that works in both directions, rework recorded as an event, and a retention period with retrieval tested.

Checks Before Release

The checks that matter are the ones performed on the product rather than on a sample kept for the purpose, because a coupon that travels with the panel is the only evidence about that panel. Where a requirement can be measured, it should be measured at the point of manufacture and recorded against the board or the lot it applies to.

A parameter that is set once and never re verified drifts, and the drift is usually discovered by a defect rather than by the record. The tooling, the material and the profile form one system, and a change to any of them should be assessed against the other two before it is released.

Where the process window is narrow, the measurement resolution has to be better than the window, or the data cannot distinguish a good part from a marginal one.