Read the stackup by region
A rigid-flex drawing should distinguish rigid-only layers, continuous flex layers, coverlay, bonding layers and any air gaps. Label each region and show where materials terminate. A single total-layer number cannot fully describe this structure.
Copper selection affects mechanics
Copper thickness and type influence resistance, routing and mechanical behavior. Rolled-annealed and electrodeposited copper have different characteristics, but suitability depends on the actual foil specification and motion requirements. Review supplier data and validation evidence for the selected construction.
Adhesives and dielectric choices
Adhesive-based and adhesiveless flexible laminates differ in construction. Review total thickness, thermal exposure, dimensional stability and processing compatibility. Select materials against the requirements rather than assuming one family is universally better.
Impedance needs actual dimensions
Use the fabricator’s proposed dielectric thicknesses, copper geometry and relevant dielectric properties. Rigid and flex regions may need different trace geometry for the same impedance target. Include coupons and an agreed measurement method when controlled impedance is required.