Rework Verdict and Scrap Decision Rules

Every rework decision is a comparison between the cost of the repair and the risk that the repair leaves a worse board than the one that was rejected. That comparison is only possible if the condition of the board is known, which is why the assessment comes before the decision.

A rule that says every defect is reworked treats a lifted pad the same as a misaligned part, and the two have very different consequences. Writing the rules down prevents both unnecessary scrap and unnecessary risk.

Assessing the Defect

The first question is what the defect is and where it is. A component on a signal net in a non critical area is a different case from one on a power plane or on a high speed pair.

The second question is whether the repair will affect the features around it, since a reworked joint changes the thermal history of the laminate and the neighbouring joints.

Repairable Conditions

A misaligned or missing component, a bridge between accessible pads and a defective part with an intact footprint are all straightforward repairs. The footprint is intact, the thermal history is manageable and the result can be inspected.

The repair should be performed with the specified technique and recorded, so that the board has a history rather than a mystery.

Conditions That Justify Scrap

A lifted pad on a fine pitch part, a damaged barrel, delamination around a reworked site and a lifted mask sliver between fine pitch pads are all cases where the repair would remove the material the joint depends on.

A board that has already been reworked more than the permitted number of times at the same site is also a scrap candidate, because the laminate has been consumed.

Cost of the Decision

The cost of scrapping is the value of the assembly, including the components already placed, while the cost of a failed repair is the same value plus the labour and the delay. The comparison is often closer than it appears.

Where the product is safety related or long lived, the risk of a marginal repair outweighs the cost of the scrap, and the rule should say so rather than leaving it to the shift.

Traceability of the Decision

Every rework should be recorded against the board identifier, with the defect, the technique and the operator. The record allows a pattern to be found, and it allows a containment to be defined if a reworked joint fails later.

A board with no rework record and an unexplained mark is a risk that is carried into the field. The recording discipline is the same one applied to labelling and traceability in general.

Acceptance Criteria for Reworked Joints

A reworked joint should be judged by the same standard as an original joint, with the addition that the surrounding area should be inspected for damage. A joint that looks correct but sits on a swollen laminate is not acceptable.

The criteria should be written into the work instruction with reference samples, so that the marginal case is decided consistently across shifts.

When to Escalate

The decision should be escalated when the defect is unusual, when the same defect appears repeatedly or when the repair would affect a critical feature. An escalation path with a named engineer is part of the process.

A repeated defect is a process problem rather than a board problem, and scrapping boards without addressing it consumes the batch one unit at a time.

Feedback to the Process

The rework and scrap data should feed the yield analysis, because a defect that is repaired rather than counted disappears from the numbers. Counting rework as a defect is what makes the improvement visible.

This is the same principle that applies to the analysis described in yield analysis, where the pattern across a panel points to the cause.

Documentation

The rule set should state the repairable conditions, the scrap conditions, the number of permitted repairs at a site and the escalation path. It should be short enough to be used at the station.

The rules should be reviewed when the product changes, since a class of defect that was repairable on one design may not be on the next.

Additional Considerations for This Build

Practical attention to scrap decision 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 scrap decision explicitly, together with the tolerance that applies, removes the assumption and keeps the result predictable from batch to batch.

Deliberate attention to rework verdict 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 rework verdict 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, escalation is the item that decides how the rest of the board is arranged. 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.

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. Running a first article through the same checks as the production panel confirms that the two agree, and that comparison is the cheapest form of process control available at prototype stage.

Related reading: our fabrication notes, board quality and design release notes cover the same ground.

A first article check confirms that the process and the drawing agree on the points listed above, and that the coupon data supports the values used in the design.

Where a measurement falls outside the expected window, the sample is retained so that the cause can be established before the balance of the batch is released.

A first article check confirms that the process and the drawing agree on the points listed above, and that the coupon data supports the values used in the design.

Where a measurement falls outside the expected window, the sample is retained so that the cause can be established before the balance of the batch is released.

FAQ

Should every defect be repaired? No. The decision depends on the footprint condition and the criticality of the net, and a rule that ignores both creates risk.

How many repairs are acceptable at one site? The limit is set by the laminate, and it is usually stated as a small number because each cycle consumes the bond between the copper and the resin.

Who should make the call? A qualified operator for the routine cases and an engineer for the unusual ones, with the escalation path documented.

Why record repairs that are successful? Because the record shows the condition of the process and allows a later failure to be traced to the repair that caused it.