Define the channel and local geometry
State single-ended or differential targets, relevant interfaces, reference conductors, routing length, and the regions where control applies. Include connector and via transitions in the wider electrical review. The impedance design guide develops these requirements; the stack drawing must then provide the physical materials and dimensions used in the model.
Impedance-stack release inputs
| Stack feature | Specify | Engineering question |
|---|---|---|
| Target | Type, nominal value and tolerance | What requirement is being controlled? |
| Geometry | Widths, spacing and reference location | Which dimensions may be adjusted? |
| Materials | Dielectric, bond and cover properties | What context supports the model? |
| Verification | Method and representative construction | How will acceptance be determined? |
Use grade-specific material inputs
Record dielectric values with frequency, method, conditioning, and typical-versus-guaranteed status. Include bonding and cover materials where they affect the trace environment. Qnity’s AP data illustrates that dielectric properties are reported in a defined measurement context. Ask the fabricator which geometry and material assumptions it will use, including finished copper and available dielectric combinations.
Agree what will be verified
Document allowable changes to trace width or spacing and who approves them. Specify the intended coupon or other verification approach and how it represents the routed region. Use low-loss material planning when channel attenuation is also important. An impedance measurement alone should not be presented as proof of insertion loss, crosstalk performance, or complete protocol compliance.
Before you release the design
- Identify every controlled region.
- Keep model and drawing materials consistent.
- Include finished-copper assumptions.
- Agree geometry-adjustment authority.
- Define validation beyond impedance when required.
Watch points
- A laminate's Dk does not specify the impedance of an unspecified trace and reference arrangement.
Practical questions
Can the fabricator adjust trace width?
Define the permitted adjustment and approval process in the release package. Uncontrolled changes can affect spacing, routing, or other requirements.
Does a rigid-board coupon represent the flex span?
Confirm that the verification construction represents the relevant flex geometry and materials. Do not assume equivalence from the same target value.
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.