A PCB fiducial and tooling-hole review should establish how the board will be located at each assembly operation, which drawing controls those references, and whether the references remain usable after the first side is populated. Send the board and panel data together. Approval of the individual circuit outline does not automatically approve the panel that a printer, placement machine or fixture will handle.
This guide is a manufacturing handoff checklist, not a universal geometry standard. Exact mark dimensions, hole tolerances, edge distances and support arrangements must be agreed with the assembler and fabricator for the selected process. The useful outcome is a documented reference scheme that both teams interpret consistently.
Distinguish optical references from mechanical location
A fiducial provides a recognizable visual reference. A tooling hole provides a potential mechanical locating feature. Neither should be treated as a substitute for the other without a process review. In its QFN and SON PCB attachment guide, Texas Instruments identifies fiducials as useful for checking component placement. That observation supports including alignment references in the review; it does not establish one fiducial layout for every board.
Ask the assembler to identify which operations use optical recognition, physical pins, edge location or a dedicated carrier. The answer may differ between printing, placement, inspection and subsequent testing. Record those differences before choosing a hole or mark that appears convenient in the layout. A mounting hole intended for the finished enclosure may be unsuitable as a process datum if its location, tolerance or access was defined for a different purpose.
Release a clear coordinate convention
Identify the drawing origin, units, top view and bottom view explicitly. Include a recognizable orientation feature in the review image. This can be an identified connector or a clearly labeled corner, provided the drawing explains the view. A note saying “bottom” is incomplete when one reader sees the board from below and another sees a mirrored top-view export.
Keep the panel reference and individual-board reference distinguishable. If placement coordinates are supplied for one circuit but fabrication data describe a panel, state who creates the repeated instances and checks their orientation. Also state who approves changes to the panel arrangement. A last-minute rotation made to improve material use can affect a previously agreed assembly setup even when the circuit itself is unchanged.
Use a reference review table
| Review item | Question to resolve | Evidence to retain |
|---|---|---|
| Board orientation | What physical feature establishes the documented view? | Annotated top and bottom views |
| Panel arrangement | Who controls circuit repetition, rotation and rails? | Approved panel revision |
| Optical references | Which marks will the assembly operation recognize? | Marked-up review drawing and assembler acceptance |
| Mechanical references | Which holes or edges locate the board? | Defined datum, tolerance and locating method |
| Second-side access | Do populated parts obstruct support or recognition? | Assembly sequence and underside clearance review |
| Change control | Which changes require renewed approval? | Named owner and revision comparison |
Use the table to collect decisions rather than simply checking that a feature exists. A drawing can contain several fiducials while leaving it unclear which ones belong to a particular circuit or panel. Similarly, a hole callout can specify a diameter without identifying its intended locating role. The reviewer should be able to explain the function of each approved reference.
Check visibility throughout the assembly sequence
Review the actual sequence, including any second-side operation. Ask whether a chosen reference remains visible and accessible when the board reaches that operation. Consider labels, carriers, fixtures and already-installed parts in the review model. Do not assume the bare-board view represents the later assembly condition.
Review any process feature placed on a removable rail against the removal sequence. If the rail is removed before a later inspection or fixture operation, that operation needs its own approved locating method. This is a coordination problem rather than an argument that every reference belongs on the finished circuit. The correct arrangement depends on the agreed manufacturing route.
Separate support decisions from alignment decisions
Knowing where the board is located does not show how it is supported. Ask how the board will be held while loads are applied during the intended operation. An acceptable optical view does not resolve interference between underside parts and a support surface. Likewise, a fixture that holds the assembly securely may obscure a reference expected by a separate inspection step.
Provide component-height information and identify any assembly restrictions that affect support. The assembler should review the proposed arrangement against its process. Avoid supplying an unverified generic support-pin map as if it were a released fixture drawing. When a carrier or fixture is necessary, give it a controlled identifier and establish who approves its relationship to the board revision.
Example: a panel revision after prototype approval
Consider a hypothetical board that was approved as a single circuit. Before production, the fabrication panel changes from one circuit orientation to alternating orientations. The circuit artwork is unchanged, so purchasing initially treats the update as administrative. However, the assembly data still assume every circuit has the same rotation.
The review should compare the new panel view with the placement setup, reference locations and circuit identifiers before releasing production. Record which deliverables changed, who checked the transformed coordinates and what first-build evidence is required. This example illustrates a possible handoff mismatch; it is not a claim that a specific machine would accept or reject that panel.
Make the approval specific enough to reuse
Save the approved panel drawing, assembly views and reference decisions with the build package. Identify unresolved questions instead of allowing a general “DFM approved” message to cover them implicitly. Revisit the approval when board dimensions, panelization, locating features or the assembly sequence change. A previous successful run is useful history but does not explain whether a changed feature was assessed.
For a design for manufacturing review, provide the board outline, fabrication data, component positions, assembly drawings and proposed panel. Use the first-build approval checklist to connect the reference review to evidence from the first assembled units. When evaluating an electronic manufacturing service, ask who signs off the shared board-and-panel package.