Choose layers for a stated routing problem
Sketch the interconnect topology before choosing a familiar layer count. Identify crossings, reference conductors, power paths, connection interfaces, and regions that must move. Compare whether more width, different component placement, or connector pin reassignment can solve routing constraints with a simpler construction. Select additional copper layers only when their electrical or packaging role is clear.
Begin with the single-layer construction and two-layer construction guides. The four-, six-, and eight-layer pages focus on progressively different planning risks rather than claiming that any particular layer count is a stocked manufacturing capability.
Stackup information that belongs in the release
| Item | Why it matters | Record |
|---|---|---|
| Copper sequence | Defines connectivity and references | Layer names and electrical roles |
| Nonconductive layers | Contribute to geometry and assembly | Film, adhesive and cover materials |
| Region map | Locates different constructions | Boundaries and section identifiers |
| Finished dimensions | Controls mechanical interfaces | Local thickness and tolerance |
| Review assumptions | Separates proposal from release | Material candidates and unresolved inputs |
Define local stacks before adding thickness
Create separate sections for the free flex, a terminal, a component area, and any rigid region. Do not carry every layer through every section by default. Coverlay openings, plated copper, bonding films, shields, and stiffeners can change what is physically present. A global thickness number can conceal the dimensions that matter to a connector or enclosure.
Altium’s rigid-flex documentation permits assigned substacks by region and describes bend angle, radius, and fold order. This supports communicating the geometry; it does not establish an acceptable bend life. Keep the mechanical model and the fabrication stack drawing consistent and independently review any transition.
Close electrical and mechanical assumptions together
For controlled impedance, agree the local dielectric geometry, copper assumptions, references, cover materials, and verification conditions before fixing trace widths. For motion, specify the actual local construction and intended path. Neither task can be completed by reading only the base-film thickness. Mark uncertain bondline thicknesses or available material combinations as open engineering questions.
Use the thickness worksheet as an arithmetic aid. It totals entered values without qualifying the construction or predicting finished tolerances. After the fabricator reviews the proposed stack, update the drawing and the model together. Preserve region names, material revisions, and approved changes so a production reorder refers to the same construction that was evaluated.
Before you release the design
- Give every distinct construction a named region.
- Number conductors consistently with fabrication outputs.
- Show all nonconductive layers in each section.
- State base and finished copper assumptions.
- Mark bend zones and connector thickness sections.
- Obtain review of the proposed stack before release.
Watch points
- A four-layer label says nothing about the number of layers crossing a particular bend.
- A CAD fold preview checks geometry but does not qualify fatigue or adhesion.
Explore this topic
Practical questions
Does layer count include coverlay?
Ordinary copper layer counts do not count coverlay as a conductor. The physical stack drawing still needs coverlay and adhesive because they affect local construction.
Should a stack be perfectly symmetrical?
Assess symmetry where it matters to processing, dimensional behavior, and bending. Deliberate asymmetry needs explicit documentation and review rather than an automatic rejection.
Technical references
References support the material or design context. Check the exact grade, part number, document revision and project conditions before release.Updated 27 September 2026 · Technical content policy · Engineering guidance supports project review; the agreed drawing defines the build.