A double - sided flexible circuit board is crafted from double - sided flexible copper - clad material, featuring coverlay openings on either one or both sides. It comprises two conductive trace layers (usually made of copper), with an insulating layer (typically Polyimide) in between. The two conductor layers are electrically linked via plated through holes (PTH). In some cases, a double - layer flexible circuit may lack PTHs, as the bottom trace is designed to enhance circuit rigidity, control impedance, or serve other specific functions.

The coverlay, made of Polyimide, is pre - cut before being laminated to the copper trace. This enables access to the trace PAD and gold fingers from both sides through the coverlay or solder mask openings. Flexible Oil can also be employed as a coverlay or solder mask to safeguard the traces from oxidation and during soldering.

Compared to a single - sided FPC and a dual - access FPC, 2 - layer flex circuits facilitate more complex circuit designs. They increase the wiring density per unit area, and by allowing components to be mounted on both sides, they achieve greater space savings.

 Stiffeners, adhesive tapes, EMI shield materials, and other components can be positioned anywhere on the double - layer circuits.