PCB assembly revision mismatch: reconciling Gerber BOM and CPL

A PCB assembly revision mismatch can survive a perfectly readable quotation package. The Gerbers show the latest board, the BOM still buys the previous connector, and the placement file locates an IC before its footprint was moved. Each file opens successfully; together they describe a product that has never been approved.

The useful release question is therefore not simply whether all three files are present. It is whether fabrication, purchasing and placement are working from one approved configuration. This guide proposes a reconciliation procedure for a turnkey build, including a small worked example and a release record that engineering can actually sign.

Freeze the configuration before comparing files

Identify the board number, bare-board revision, assembly revision and population variant separately. A single PCB can support several assembled products, and an assembly-only component substitution need not change copper. Record those relationships rather than forcing every identifier to match the same letter.

Create one release directory from the approved design state. Export the manufacturing outputs into it and remove superseded exports from the deliverable archive. Include a manifest listing each filename, its purpose, the generating design revision and its checksum. A checksum detects a changed file; it does not prove that the file was correct when generated. Keep the engineering approval as a separate record.

Use the assembly release-file guide to establish the basic package. The reconciliation below adds a cross-file consistency check to that package, rather than replacing fabrication drawings or purchasing specifications.

Compare reference designators before comparing totals

Expand grouped BOM entries into individual references for checking. A row containing R1, R2 and R8 represents three locations even when all use the same manufacturer part number. Flag repeated references, references that appear in more than one BOM row and a listed quantity that disagrees with the expanded reference count.

Build separate sets for populated surface-mount parts, manually assembled parts, unpopulated options and non-component features. Fiducials, mounting holes and tooling markers should not be mistaken for missing purchased components. Conversely, a connector installed by hand still needs an accountable BOM entry and assembly instruction even if it is intentionally excluded from machine placement.

The KiCad 9.0 PCB Editor documentation describes placement-export controls for SMD-only output, DNP parts, through-hole pads, units and origin. These options explain why two valid exports can contain different reference sets. Record the selected options and agree the required inclusion policy with the assembler. A missing row should have a documented reason.

Resolve a mismatch by location and consequence

Consider this illustrative release review. Revision C changes a sensor interface, but somebody reused the previous BOM and position export. The reference count alone might still look plausible.

Do not solve U3 by silently choosing whichever file arrived most recently. A later email timestamp is not engineering approval. Return the discrepancy to the person responsible for the released configuration, record their disposition and replace the complete affected output set. Preserve the rejected package for traceability, clearly outside the active production directory.

Check geometry independently of the BOM

The BOM can establish what to buy without proving where it belongs. Overlay the placement information on the released board view, using a viewer or assembler review that supports the supplied formats. Check several asymmetric landmarks, including a connector, a polarized device and a component near the opposite corner. Confirm both board sides.

Document units, coordinate origin, side naming and rotation convention. An apparent global shift often calls for an origin investigation; many isolated movements suggest a different revision or component-specific interpretation. Neither pattern justifies an automatic correction without checking the source design. Bottom-side placement deserves explicit review because the viewing convention can make a plausible image misleading.

For each polarized or pin-numbered device, relate the placement angle to the actual footprint and assembly drawing. A spreadsheet containing a numeric angle is insufficient evidence that pin 1 will land correctly. Ask the assembler to return a placement preview for engineering approval when conventions are uncertain, especially during prototype assembly review.

Separate a purchasing change from a design change

A supplier may propose a substitute after the release has been approved. Record the original part, proposed manufacturer part number, affected references and approval status. Check package, pinout and application requirements; sharing a nominal value or footprint label does not establish equivalence.

If the substitution changes placement, stencil requirements or an inspection criterion, update those deliverables as well as the BOM. If it changes only an approved purchasing option, document that limited scope. The release owner should be able to explain why unchanged files remain valid. Avoid sending a new BOM with an instruction to use everything else from an unspecified earlier email.

Use a release manifest that survives an email handoff

A manifest should let a reviewer identify the exact package without opening every manufacturing file. Give the archive a release identifier and list the board number, assembly revision, variant and approval date inside it. For each output, record its filename and role. Include the assembly drawing and test instructions in the same review even when they are delivered separately. The manifest then describes the complete release rather than only the contents of the Gerber folder.

For a controlled change, add a short impact statement. For example, explain that a connector has moved, the corresponding placement file and assembly drawing have changed, and the purchasing part number remains approved. That statement does not substitute for checking the geometry. It directs the reviewer to the expected differences and makes an unexpected BOM change easier to recognize. Keep the change description specific enough that another engineer can verify it without consulting the original author.

When a supplier returns a corrected manufacturing file, retain both its proposed version and the approval decision. Identify whether the correction changes only manufacturing presentation or changes the intended product. An adjustment made to support a production machine may still need engineering review if it alters the meaning of a placement instruction. Do not let the supplier’s working copy become the new design master without a deliberate decision.

Distinguish an approved panel from the single-board release

Panelization creates another representation of the same design, so record the relationship explicitly. Identify which single-board release the panel contains, the number of board instances and the approved orientation of each instance. Include the panel drawing and any tooling features added by the fabricator. A valid single-board placement file does not by itself describe the complete panel arrangement used by the assembly line.

Ask the assembler to confirm whether it expects single-board coordinates or panel-level coordinates. Retain the approved convention with the placement preview. If the production system generates repeated instances, make sure reference designators are associated with the correct board instance rather than appearing as unexplained duplicates. The review should distinguish a repeated R1 on another board from an accidental second placement of R1 on the same board.

Check a proposed panel revision against downstream fixtures and inspection programs. A tooling-hole or rail change may leave the circuit unchanged while affecting how the assembly is held or located. Record which programs and fixtures need review and who confirms readiness. This avoids approving a new panel solely because the copper inside each board outline appears identical.

Close the discrepancy with evidence, not an email subject

A useful closure entry includes the discrepancy identifier, the affected reference or drawing feature, the approved decision and the exact replacement files. The release owner should be able to select a closed item and demonstrate where its resolution appears in the final package. A message saying “all fixed” without an identifiable output is not enough to establish what production should load.

Before sending the corrected archive, open it as the recipient will receive it. Confirm that the expected files are present, no temporary exports have been included and the manifest matches the filenames. Verify that a password-protected or separately transferred package has an agreed delivery route; do not place sensitive access information in the manufacturing documents themselves. The receiving team should acknowledge the package identifier before the affected work resumes.

For a late change after material purchasing or board fabrication has started, include a disposition for work already in progress. Engineering must decide whether existing boards and purchased parts remain usable, require rework or must be held. That disposition belongs with the order and release record. A corrected drawing only controls the next action; it does not automatically resolve material produced under the earlier revision.

Finally, retain the first-article findings against the same release identifier. If the first assembly reveals another discrepancy, reopen the relevant issue or create a linked change instead of altering the files without a trace. The next order should start from the approved outcome of that review, with the old package clearly marked as superseded.

Make the production hold explicit

A discrepancy list should contain an owner, affected file, reference designator, proposed disposition and closure evidence. Mark whether purchasing, fabrication, assembly or all stages are held. This prevents a harmless drawing clarification from unnecessarily stopping procurement, while ensuring a package mismatch cannot proceed merely because components have already arrived.

Before authorizing the build, confirm that the active archive has one manifest; every population exception is explained; the placement preview matches the approved design; substitutions have written decisions; and the assembler has acknowledged the release identifier. Use the release-file checklist to track remaining inputs, then retain the reconciled package alongside the order.

When you request a project review, include the board and assembly revisions, variant, quantity and unresolved discrepancies. A quotation can then identify the work still needed before release instead of assuming that individually readable files describe a consistent assembly.