SMT Data Collection and Traceability Records

Traceability is the ability to answer a question about a board after it has been built: which paste, which profile, which machine, which operator. The records that answer those questions are worth keeping and the rest are noise.

Starting From the Question

The useful questions are the ones that arise during a field failure investigation or a recall. Which lot of paste, which oven profile, which feeder position supplied the part, which revision was built.

Each question names a record. Our failure investigation notes describe how the questions arise.

Carrying the Identity of the Board

A serial number or a lot code has to travel with the board from the first station to the last, and it has to survive the processes in between. A label applied after reflow cannot identify the reflow.

The identifier should be applied at the earliest practical point. Our floor control notes describe the arrangement.

What Each Station Should Record

The printer records the paste lot, the stencil and the print parameters. The placement machine records the program, the feeder setup and the nozzle set. The oven records the profile and the recipe.

The records are useful when they are linked to the board identity. Our fabrication notes list the points to confirm.

Recipe and Program Control

A recipe that can be edited at the machine is a recipe that can drift. The recipe should be controlled centrally and recalled rather than adjusted in place, with any change recorded.

Recipe changes are a common cause of an unexplained yield shift. Our yield analysis notes describe the analysis.

How Long to Keep the Records

The retention period should follow the product life plus the period in which a claim is possible, rather than a single figure for every record. Board level records are usually kept far longer than station parameters.

The retention should be stated in the procedure. Our quality notes describe how the records are held.

Serialisation and Its Limits

Serialising every board gives the finest resolution and it costs a marking and a reading step at every station. Where a lot code is enough, it is the cheaper choice.

The choice follows the consequence of a failure. Our component selection notes describe the traceability the supplier provides.

Verification

The verification is a set of records that answers each of the questions identified at the start, an identifier applied before the first process it has to describe, and a centrally controlled recipe with changes recorded.

Our quality notes describe how the records are kept.

Process Control and Verification

Keeping a sample from the panel turns a dispute into a measurement, because the same coupon can be re-examined by both parties without rebuilding the batch. Reviewing the design before the data is released is cheaper than correcting it after the panel is in the tank, because every step downstream inherits the decision made at the front end.

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.

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. A record that identifies the operator, the date and the settings is worth more than a record that identifies only the result.

The acceptance criteria should be written before the work starts, so that the decision is made by the specification rather than by the person inspecting.

FAQ

Is full serialisation always necessary? It is necessary where a recall has to reach individual units. Where a lot can be recalled as a group, a lot code is sufficient and cheaper.

Does the record have to be electronic? Paper works if it is retained and legible, and electronic records are easier to search and harder to lose.

What does gopcb provide for traceability? We provide an identifier applied before the first process it describes, station records linked to that identifier, a centrally controlled recipe with recorded changes, and a retention period stated for each record type.