How it works: the formula and limits
Total (mm) = Σ copper (µm) / 1000 + Σ dielectric (mm). Difference = total − target. Within band if |difference| ≤ target × tolerance / 100.
Diagram copper thickness is exaggerated for readability. No impedance, thermal, warpage or compliance simulation is performed.
Build the conversation before the board
A stackup is the ordered construction of copper and insulating layers through a printed circuit board. Circuit Edge Technologies uses this workspace to make early construction decisions visible: how many circuit layers are planned, which layers carry signals or planes, and how the thickness budget is distributed. The result is a review brief, not a purchase specification. A fabricator must still translate the concept into stocked cores, available prepregs, copper foils and a controlled lamination process. Keeping those two stages separate prevents a neat drawing from being mistaken for a released manufacturing instruction.
Start with an editable layout
Choose a two-, four-, six- or eight-layer starting layout. Each preset replaces the current stack and starts with a copper-plus-dielectric total of 1.600 mm. These are illustrative, symmetric thickness budgets rather than supplier-approved constructions. The presets intentionally use simple round dimensions so the arithmetic is easy to inspect. Choose a starting point based on routing needs and reference-plane planning, then replace every thickness with the values your supplier proposes. Changing the preset resets the material family, target and tolerance as well as the layers.
Read the editor from top to bottom
The editor alternates copper rows labelled L1, L2 and so on with dielectric rows labelled D1, D2 and so on. Assign a Signal, Ground, Power or Mixed role to each copper layer. Change each insulating section between Core and Prepreg to record the intended construction. Labels document intent; they do not verify that a layout contains a continuous ground plane or that two power domains are correctly isolated. The cross-section follows the same order, making it easier to compare a table entry with its physical position before sharing the brief.
Understand the thickness calculation
The calculation is deliberately transparent: total thickness equals the sum of all entered copper thicknesses plus the sum of all entered dielectric thicknesses. Copper inputs are in micrometres and are divided by one thousand before summation in millimetres. The optional mil display uses one mil equal to 0.0254 mm. This model excludes soldermask, surface finish and changes associated with pressing or resin flow. If a supplier specifies overall finished thickness differently, reconcile that definition before comparing the number here with a purchase drawing or acceptance tolerance.
Worked example: a four-layer budget
The four-layer starting layout uses four copper layers of 35 micrometres each. Together they contribute 0.140 mm. The dielectric sections are 0.200, 1.060 and 0.200 mm, giving 1.460 mm of insulation. Adding those totals produces 1.600 mm. With a target of 1.600 mm, the difference is zero. If only the first dielectric is changed to 0.300 mm, the calculated build becomes 1.700 mm and the mirrored thickness check asks for review. That change may still fall within a wide user-entered thickness band, illustrating why target matching and symmetry are separate checks.
Treat tolerance as an input, not an industry promise
The target comparison uses the tolerance you enter: the permitted difference is target thickness multiplied by tolerance percentage divided by one hundred. The default ten percent is an editable example, not a guarantee that a supplier accepts that limit. Set the tolerance from the agreed requirement and check the supplier measurement method, sampling and location. A matched thickness comparison says only that the arithmetic sits inside your chosen band. It says nothing about the final board yield, material quality, assembly fit or electrical performance.
What the symmetry flag actually checks
The builder compares mirrored copper thicknesses, mirrored dielectric thicknesses and mirrored dielectric types about the centre of the stack. It does not compare actual copper artwork, resin content, glass styles, local copper distribution or mechanical stresses. Two layers with matching thickness can still have very different copper coverage. A matched flag is therefore useful for catching an obvious entry mismatch but cannot predict bow or twist. If a deliberate asymmetric construction is required, retain the flag in the review brief and ask the fabricator to assess the complete process rather than hiding the difference.
Connect layer roles to return paths
Plane planning belongs alongside routing planning. A layer named Ground can still be split, perforated or missing under a critical route. Before layout release, identify the reference conductor for each important signal, inspect connector transitions and decide how return current crosses between reference layers. This builder records a layer role without simulating those paths. It also does not calculate impedance. Use the companion impedance estimate for a separate geometry study, and ask for the supplier-approved geometry and coupon requirements when controlled impedance is part of the project.
Carry material questions into the stackup review
The material selector and stackup builder answer different early questions. The selector helps identify which construction families deserve comparison; this editor records one proposed layer arrangement. A generic FR4 or RF family label does not supply a dielectric constant, loss tangent, glass-transition temperature or reliability rating. Replace the family note in your manufacturing documentation with an exact approved grade and construction. Confirm availability, pressed thicknesses, copper specification and assembly conditions together. An attractive material datasheet cannot compensate for a stackup that the intended supplier cannot manufacture consistently.
Export a brief that another engineer can reproduce
Use the PDF brief, CSV or Copy action to retain the selected family, target, tolerance, ordered layer entries, calculated total and review flags. Share link encodes the stackup in the URL so another visitor can reproduce those values. Links and downloaded files contain the entered construction data; avoid treating them as a secure project repository. The website does not automatically submit the brief to Circuit Edge. For a project review, send the appropriate documents through your agreed contact channel and include the board revision, interface requirements and supplier proposal.
A practical release checklist
Before fabrication, confirm the exact material grade, copper thickness definition, pressed dielectric values, finished board thickness tolerance and any controlled-impedance requirements. Check copper balance, drill and via construction, soldermask assumptions and the relationship between mechanical drawings and fabrication notes. Keep the approved supplier stackup beside the PCB project so a later material substitution or layer edit triggers another review. Circuit Edge Technologies can support the layout and handoff conversation; this tool helps organize that work while leaving fabrication approval with the responsible project team and supplier.
Continue with the material selection workspace, impedance estimate or Circuit Edge stackup design note.
Stackup builder questions
Is this a fabrication-approved stackup?
No. Starting layouts are illustrative thickness budgets. Confirm the exact construction with your fabricator.
Does the total include soldermask?
No. It sums entered copper and dielectric thicknesses only, excluding soldermask, surface finish and resin-flow changes.
Can I edit every layer?
Yes. Edit the role and copper thickness of each circuit layer, plus the type and thickness of every dielectric section.
Does symmetry mean the board will not warp?
No. The check compares mirrored thicknesses and dielectric types. Actual copper coverage and manufacturing stresses are not modelled.
Does this tool calculate impedance?
No. Use the linked impedance estimate separately and confirm controlled geometry with the fabricator.
What does the target tolerance mean?
It is your chosen comparison band, not an industry guarantee or a supplier capability statement.
How can I save or share a stackup?
Export PDF or CSV, copy the brief or create a share link that encodes the input stackup in its URL.