Flexible regions need a material construction selected for the bend condition, assembly history and electrical requirements. Polyimide alone is not a complete flex specification.
What to consider
Adhesive system, copper type, coverlay, layer count and local stiffeners change mechanical behavior. The rigid sections may use a different but compatible material system. Keep bend regions, transitions and via structures visible in the mechanical and fabrication drawings.
A practical review example
For a cable-like flex region between rigid islands, define the installed bend radius and whether movement repeats in service. Ask for a construction supported by appropriate bend and assembly evidence.
Checks before release
- Identify static versus dynamic flex.
- Review copper grain and foil choice with the supplier.
- Keep via and stiffener transitions out of unapproved bend zones.
Connect this decision to fabrication
Use the material selector to organize the initial discussion. Keep proposed values separate from the approved drawing and document the effect of any change on the rest of the construction.
- Identify the exact grade, glass style, resin content and copper foil.
- Compare Dk and Df only with their frequency and test method.
- Confirm the material system is qualified for the proposed via structure.
Technical references
FR408HR material and processing resourcesMEGTRON6 material family and test conditionsRO4000 laminate data and processing resourcesReferences checked 2 October 2026. Manufacturer data describes its stated construction and is not an HDIPCB.org manufacturing commitment.