Assign a purpose to each copper layer
Decide whether the second layer provides crossings, a reference, power distribution, or an additional connection surface. Review routing and return paths together. A continuous reference and a patterned reference can create different electrical and mechanical questions. Use reference-conductor planning before treating the second layer as a generic ground fill.
Two-layer construction review
| Stack feature | Specify | Engineering question |
|---|---|---|
| Layer roles | Routing, reference or power | Is the second layer solving a defined problem? |
| Interconnection | Via type and location | Which regions carry plated features? |
| Finished copper | Foil plus process contribution | What enters thickness and bend reviews? |
| Protection | Top and bottom materials and openings | Are local sections different? |
Define interconnects and copper build
Locate plated holes and identify which vias can remain outside moving regions. Ask the fabricator to explain the proposed base foil and plating contribution to finished copper. The via design guide helps connect hole placement to local mechanical duty. Draw coverlay openings and any reinforcement around joining or connector regions.
Review the actual bending section
A two-layer design can have different copper coverage and protection on each side. Include both in the local stack and mechanical review. Compare the intended installed geometry with a representative specimen, especially where a via field or supported region meets free flex. If electrical requirements change the copper pattern, revisit the mechanical assumptions instead of treating stackup review as a one-time task.
Before you release the design
- Name both copper layers consistently.
- Map vias against the motion region.
- Separate base and finished copper.
- Include top and bottom protection in totals.
Watch points
- A two-layer stack with vias should not be evaluated as two bare copper foils on film.
Practical questions
Is the second layer always a solid plane?
No. Choose its role from routing, return-path, power, and mechanical needs, then document the copper pattern.
Can the same thickness describe the terminal and free span?
Only if their actual sections match. Otherwise define both regions separately.
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.