Part of the rigid-flex circuit board resource.
The finished construction combines flexible laminate, copper, protective coverlay, bonding materials, rigid dielectrics, finishes, and sometimes stiffeners. A trade name or a generic phrase such as “polyimide board” does not define that stack. Record the exact material requirements or clearly allow a qualified equivalent subject to review.
Adhesiveless and adhesive-based laminates
An adhesiveless flexible laminate avoids a separate bonding adhesive between copper and its flexible dielectric. An adhesive-based construction includes that interface. The choice changes thickness, mechanical behavior, and processing considerations. It does not mean that every other adhesive, such as the coverlay adhesive, disappears from the board.
Choose copper by duty and grade
Rolled annealed and electrodeposited copper are manufactured differently, but the label is only the start of a specification. Review foil thickness, elongation, surface treatment, grain orientation, and whether the conductor receives additional plating in the bending region. For repeated movement, qualify the actual construction rather than applying an invented RA-to-ED multiplier.
Coverlay is part of the bend
Polyimide coverlay and its adhesive add to the finished flex thickness. Openings need registration allowance and adequate conductor capture where appropriate. Local adhesive buildup, pad openings, or abrupt coverlay terminations can alter stress and assembly behavior. Obtain the proposed opening geometry from the fabricator’s process review.
Bonding and stiffeners have different jobs
Controlled-flow or no-flow prepreg helps build the rigid region while managing resin near exposed flex. A stiffener gives local mechanical support; it does not by itself add the plated interconnections of a true rigid region. Place stiffener edges with the bend and strain-relief design in mind.
Ask for data that matches your requirement
Working temperature, assembly exposure, moisture, dielectric behavior, flammability, and substance restrictions need material-specific evidence. Tg alone is not an operating-temperature rating. A halogen-free claim should cover the relevant complete system. Use the material selector to organize these questions, then approve the exact proposed stack.
Next steps for your project
Connect this review with the regional stackup, material choices, and design checklist. Use the design workbench to organize initial parameters, then send the project for a quotation review.