Separate connection need from convenient placement
List the layer changes that are electrically necessary and locate their proposed vias on the regional drawing. Consider whether routing can bring them into a stable supported area. Review conductor paths before adding layer transitions simply to shorten a route. A CAD tool can permit a via without understanding how that location moves in the product.
Via review by function
| Review item | Design question | Evidence or action |
|---|---|---|
| Signal layer change | Can the transition occur outside the active span? | Compare routing alternatives |
| Thermal or power connection | What electrical or thermal path is intended? | Document load and construction assumptions |
| Test access | Will probing damage or load the flexible area? | Define a supported probing arrangement |
| Exposed hole | Does coverlay intentionally leave it accessible? | Coordinate opening and registration requirements |
Describe the plated structure
Identify which layers are connected, whether the hole is plated, and how local copper buildup is represented in the stackup. Check exposed annular areas and coverlay access with the fabricator. Use actual agreed hole and land rules; do not assume a rigid-board default is suitable for a different flex process or construction.
Review nearby mechanical discontinuities
Inspect the relationship among a via, stiffener edge, fold region, mounting point, and component pad. If the feature cannot leave a loaded region, call it out as a specific review and validation item. Agree what inspection or sectioning evidence is needed for the prototype. Keep those requirements separate from the electrical test, which answers a different question.
Before you release the design
- Mark via locations on the mechanical region map.
- Confirm plated and non-plated holes are unambiguous in output files.
- Review hole, land, and coverlay requirements as a set.
- Assign representative inspection to any unusual interconnect feature.
Watch points
- A passing netlist test does not demonstrate mechanical endurance of a via.
Practical questions
Are vias forbidden on all flex circuits?
No. Many flex constructions use interlayer connections. Their structure and location must fit the construction and duty; blanket placement rules cannot replace a regional review.
Can I tent every via with coverlay?
Discuss the actual insulation process and intended access with the fabricator. Coverlay openings, adhesive behavior, and assembly requirements differ from a rigid-board solder-mask assumption.
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.