HDI rigid-flex design and transition regions

What to consider

Avoid assigning dense via structures to a bend region without a qualified construction. Define the rigid-to-flex transition, coverlay openings, stiffeners and the intended bend condition. Static installation bends and repeated dynamic flexing require different mechanical evaluation. Microvia capability in a rigid section does not establish flex reliability.

A practical review example

For a compact wearable, separate the rigid component islands from the flexing connection. Show the allowed bend zone and assembly folds in the mechanical drawing before the factory proposes the laminate system.

Checks before release

1. Document bend location and whether flexing is static or dynamic.
2. Review copper type and local layer count.
3. Keep transition and stiffener geometry explicit.

Connect this decision to fabrication

Use the design checklist 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.

• Use rules confirmed for the chosen factory and construction.
• Inspect return paths through every critical breakout.
• Release consistent artwork, drills, stackup and drawing revisions.