ENGINEERING & SOURCING GUIDES
Approving a PCB Stack-Up Drawing
Approve a PCB stack-up drawing only when it identifies the released board revision, maps every copper layer to the manufacturing files, defines the proposed materials and finished geometry, and resolves the electrical and fabrication requirements affected by that construction. Record exactly which drawing revision is approved and which changes need another review. An email saying “stack-up looks fine” is difficult to use if several different drawings remain in circulation.
This guide covers the approval record for a rigid multilayer board. It does not select a universal layer arrangement or calculate impedance. For the broader construction discussion, start with the multilayer PCB guide; use the steps below when reviewing a specific supplier proposal.
Identify the document that will control the build
Start with the title block and the file package. Record the board number, board revision, stack-up document number and revision, supplier proposal reference, date and units. A supplier’s internal construction number can help identify its proposal, but it should not replace your board revision. Keep the final approved document with the released fabrication files.
Ask which document takes precedence if the drawing, quotation and manufacturing package disagree. Resolve the conflict before approval instead of asking production to choose. If a proposal changes after review, give it a new identifiable revision and retain a short change list. Approval should name that revision, not just the attachment’s generic filename.
Altium’s layer-stack documentation describes a table containing the design’s layers, materials, thicknesses and dielectric constants. Such an export is a useful starting point. The reviewer still needs to compare the exported drawing with the construction the supplier actually proposes to manufacture.
Review the stack from top to bottom
Read the drawing as an ordered list, starting at the designated top side. For each copper layer, match its number and name to the corresponding manufacturing-file layer. Then examine the dielectric entry between that layer and the next. This catches ambiguous labels such as “inner signal” repeated without a layer number.
| Field | What the proposal should identify | Hold approval when |
|---|---|---|
| Layer identity | Top-to-bottom copper order, layer names and matching file layers. | The supplier’s numbering cannot be reconciled with the released data. |
| Dielectric construction | Core or prepreg designation, material identity and proposed construction between copper layers. | An unspecified alternative could change an approved design assumption. |
| Thickness | Relevant finished dielectric dimensions, overall thickness, units and acceptance tolerances. | The drawing mixes incoming-material dimensions with finished dimensions without explanation. |
| Copper | Which values describe starting foil, nominal finished copper or a required finished minimum. | A thickness or copper-weight label has no defined basis. |
| Electrical requirements | Controlled structures, signal/reference layers, targets, tolerances and agreed verification. | A target is stated without identifying the geometry or layers to which it applies. |
| Via and drilling constraints | Applicable layer spans and any construction-dependent drilling requirements. | A proposed change has not been reconciled with the drilling documentation. |
| Approval scope | Approved revision, deviations, responsible approver and affected order or build. | Open items are treated as permission to proceed. |
Keep an “open items” column in the review record. A blank value should mean “not provided,” not “supplier may choose.” Where a field does not apply, mark it accordingly so the next reviewer can distinguish a deliberate exclusion from an omission.
Clarify the basis of every thickness and copper value
Ask whether each dielectric dimension is the intended finished separation in the board or a nominal material input. Confirm how the supplier relates its selected materials to the finished construction. Also define the basis of the overall thickness: which layers are included, where it will be measured and what acceptance range applies. Do not add incompatible nominal values and assume the sum establishes the finished-board requirement.
A supplier example illustrates why the terminology matters: Eurocircuits’ Buildup Editor guide distinguishes core thickness from outer-layer copper start and final thickness. Its microsection explanation notes that processing can remove copper and plating can add it. These references explain the distinction; their service-specific tolerances are not adopted as requirements for your order.
For the review record, use a clear label such as “outer copper: required minimum after processing,” followed by the project requirement and units. If the supplier instead lists starting foil, ask it to state the finished value it is offering. Review inner and outer copper separately, and reconcile these entries with the fabrication notes. A commercially familiar “1 oz” label does not resolve every acceptance question on its own.
Tie electrical requirements to identifiable structures
An impedance target belongs to a defined structure. Record the signal layer, reference layer or layers, single-ended or differential requirement, target and tolerance, and the proposed conductor dimensions. Include the relevant material data source and modeling assumptions in the supporting record. Ask who approves geometry changes if the fabricator proposes adjustments.
The official Altium Layer Stack Manager documentation treats impedance profiles, assigned layers and reference layers as explicit settings. It also defines via types by their layer spans. Those are useful review prompts: a drawing with the correct layer count can still leave important electrical or drilling relationships unresolved.
Use construction-specific dielectric information where the design requires it. For example, Isola’s FR408HR tables, revision G dated January 5, 2026, organize core and prepreg data by construction and frequency. Record which entry and conditions support the proposed model; do not substitute a headline material value without review. The separate FR-4 selection guide explains how to evaluate grade identity and substitutions.
Agree how the specified requirement will be checked. Where impedance testing is required, identify the applicable coupon or test structure, acceptance requirement and report expected with the order. Keep calculated results separate from measured acceptance evidence. Neither a model output nor a drawing approval by itself proves that delivered boards meet the requirement.
Use a change table instead of a vague approval
Compare the latest proposal against the last reviewed revision. Separate administrative corrections from changes that affect geometry, materials or verification. Route each technical difference to the person responsible for that requirement. Procurement can track closure, but it should not silently approve an electrical design change because the revised quotation has the same price.
| Proposed change | Question to resolve | Recorded outcome |
|---|---|---|
| Drawing B changes the L1–L2 finished dielectric entry from 0.10 mm to 0.13 mm. | Has the electrical owner reviewed the affected structure using the revised geometry? | Hold pending the updated model and any approved routing adjustment. |
| The material column changes from a named grade to “equivalent.” | What exact grade and construction are proposed, and which substitution rules apply? | Hold until the alternative is identified and reviewed. |
| The title block corrects a misspelled project name; all technical fields remain unchanged. | Does the correction preserve the correct board number and revision? | Record the correction and identify the final drawing revision. |
Example only: these hypothetical entries describe a review situation, not a customer case or suggested stack-up. The two dielectric numbers are invented inputs for the example. No impedance result is inferred from them, and neither dimension is presented as a manufacturing capability.
Suppose the supplier resolves the first two entries and issues Drawing C. Approve C explicitly and archive B as superseded. If an earlier purchase order refers to B, update the order’s document reference as well. Otherwise, design and purchasing may have approved different constructions despite closing the same email discussion.
Close the release record and define reapproval triggers
Before authorizing the build, confirm these items together:
- The board number, revision and manufacturing-file package match the approved drawing.
- Every copper layer maps unambiguously to the intended file layer.
- Material identities, dielectric dimensions, copper definitions and thickness tolerances are resolved.
- Electrical and drilling requirements affected by the construction have responsible-owner approval.
- Required measurements, reports and traceability records are identified.
- All deviations are either approved explicitly or removed from the proposal.
- The supplier has acknowledged the final drawing revision and substitution restrictions.
State whether approval covers one prototype lot, a particular order or repeat production under defined conditions. Require another review when a supplier proposes changes to controlled materials, dielectric geometry, copper requirements, layer mapping or other approved assumptions. Do not infer that a past prototype approval automatically covers a revised production construction.
The quality evidence guide helps organize delivery records. Keep those requirements in the same release package as the drawing and the files needed for a PCB quotation. The resulting record should let another team member identify what was approved, what was built and what evidence was requested without reconstructing an email chain.
Prepare a stack-up inquiry
Include the board revision, current stack-up drawing, layer files, material and copper requirements, finished thickness, controlled-impedance requirements, via details and quantity. Attach the unresolved-item list and state which changes require approval so the proposal can address the actual design constraints.
Frequently asked questions
Is a CAD stack-up export enough for manufacturing approval?
It is a useful design record. Compare it with the supplier’s proposed materials and finished construction, close discrepancies, and identify the exact drawing revision authorized for the build.
Does matching the total board thickness prove the stack-up is equivalent?
No. Review the individual layers, dielectric construction, copper definitions and affected electrical or drilling requirements. The same total thickness does not establish that those fields match.
Can the fabricator change trace dimensions to meet impedance?
Define that permission explicitly. Identify which structures and limits it covers, what revised dimensions must be reported, and who approves the resulting proposal before fabrication.
What should an approval message identify?
Name the board and drawing revisions, the released file package, approved deviations, approval scope and remaining hold conditions. Obtain supplier acknowledgement of the same document set.
Primary sources checked October 8, 2026. Supplier and CAD documentation are cited for specific technical distinctions. The approval workflow, checklist and hypothetical change record are editorial guidance, not a substitute for project-specific engineering approval.