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Begin with the functions of the copper layers

Identify signal, reference and power roles and the relationships between them. Determine which dielectric intervals affect critical impedance, timing, insulation or mechanical requirements. Those functions help explain why a material or thickness is fixed rather than chosen only to reach a nominal total board thickness.

Keep the electrical design model connected to the physical layer list. If a signal changes reference or passes through a transition, preserve that context in the review. Material selection should support the intended channel and return structure rather than become a separate purchasing exercise.

Physical thickness entries

Distinguish cores and pressed bond intervals

A cured core has a supplied thickness convention, while a bonding interval needs a fabricator-reviewed finished construction. Do not treat a glass style or an unpressed material dimension as a guaranteed finished dielectric thickness.

Use the PCB core page for over-copper versus over-dielectric dimensions and the fiberglass fabric guide for reinforcement context. Record each physical contribution once. Copper should not be included in a core number and then added again as a separate layer in the same total.

Assign the exact material and allowed alternatives

For each interval, identify the grade, supplied form, relevant electrical-data basis and any nonnegotiable requirements. If alternatives are allowed, state the conditions they must satisfy and the approval owner. A general or equivalent note is weak when it hides which properties actually control the design.

Keep the material list and stackup at the same revision. A proposed substitution may affect geometry, processing or qualification even if its nominal thickness is similar. Review those consequences before release rather than accepting a total-thickness match as proof of equivalence.

Stackup thickness interval sum

Use a transparent thickness record

The worksheet accepts layer label, nominal thickness, negative deviation and positive deviation in millimetres. The deviations are positive absolute amounts, not percentages. Each physical contribution appears once, and labels must be unique.

It sums nominal values and arithmetic lower and upper limits. This is a worst-case interval calculation, not a statistical tolerance model. It does not infer how resin flow, copper pattern, pressing or measurement location affect the finished board. Those questions need the proposed manufacturing construction.

Worked example: the basis of a total matters

Assume a simple three-entry record with 0.035 mm top copper, 1.53 mm dielectric and 0.035 mm bottom copper. With 卤0.005 mm on each copper entry and 卤0.10 mm on dielectric, the nominal total is 1.60 mm and the arithmetic interval is 1.49 to 1.71 mm.

These values are hypothetical input tolerances, not a recommended board tolerance or a process promise. If a supplier quotes a finished-board tolerance directly, do not assume that summing unrelated material tolerances reproduces its basis. Clarify the measurement and acceptance convention in the fabrication drawing.

Review electrical and process compatibility together

If one region needs a different electrical material, review its interaction with adjacent bonding and core materials. A hybrid construction can introduce process and dimensional questions beyond the individual datasheets. Keep the proposed build sequence and material compatibility in the engineering discussion.

The laminate loss guide helps interpret electrical data without reducing selection to a category label. Ask the fabricator which construction supports the intended geometry and what evidence is needed. A favorable Df or Tg alone does not approve the complete stackup.

Control the final stackup across the file package

The approved stackup should agree with the fabrication drawing, impedance requirements, drill structure and material list. Preserve the revision used by the electrical model and any acceptance coupon. When a change is negotiated, update the controlled documents together.

For repeat orders, identify what can remain a supplier process choice and what requires approval. This avoids both unnecessary restrictions and uncontrolled substitutions. The objective is a reproducible construction with clear responsibility, not a drawing overloaded with unrelated material names.

Send an answerable construction request

Provide the layer functions, physical target, material constraints, copper, critical electrical requirements, quantity and acceptance scope. Mark dimensions that may change after review and identify the ones fixed by connectors or mechanical interfaces.

The thickness worksheet is an optional discussion record. A final proposal should state the actual materials, finished dielectric intervals, tolerance basis and open exceptions. That gives the design and procurement teams a common construction to approve before manufacturing begins.

Release materials and geometry as one controlled stackup

A stackup is an agreement about physical construction, not just a vertical list of copper layers. Give each dielectric interval an identity and distinguish cured core thickness from the pressed thickness of bonding material. State whether copper is included in every quoted dimension.

Review the implications of a material change across impedance, lamination, drilling, registration and assembly exposure. A replacement with a similar headline Tg or Dk can still require a different geometry or process. Preserve the approved layer order, copper distribution assumptions and measurement basis with the manufacturing files.

Use the worksheet to organize a review, then obtain the fabricator's proposed construction and tolerances. Close differences before release. The final stackup, drawing and procurement material list should reference the same revision, especially when multiple suppliers or repeat orders are involved.