FPCmanufacturer learned that，Double-sided flexible circuit board consists of double-sided flexible copper clad material with coverlay opening on one or two sides.There were two conductive trace layers (normally copper) with an insulating layer (normally Polyimide) in the middle, and two conductor layers were electronically connected via plated through holes (PTH). Sometimes, there’s no PTH in the double-layer flexible circuit, as the design purpose of the bottom trace is to support the rigidness of the circuit, impedance controlled, or another special purpose.

The coverlay was made of Polyimide and already pre-cut before being laminated to copper trace so that the trace PAD and gold fingers can be accessed from both sides through the coverlay or solder mask opening. Flexible Oil also can be used as coverlay or solder mask to protect traces from oxidation and soldering.

2 Layer flex circuits allow for more complicated circuit designs than a single-sided FPC and a dual access FPC, increase the wiring density per unit area, and further space savings are realized by mounting components on both sides.

All stiffener, adhesive tape, EMI shield material and other materials can be placed on anywhere of the double layers circuits.

PCBsupplierChina learned that，Capability of Double Side Flexible Circuit:

Copper thickness: 1/3OZ, 1/2OZ, 1OZ, 2OZ, 3OZ, 4OZ

Polymide thickness (in base material): 1/2mil, 1mil, 2mil, 3mil, 4mil

Board thickness: 0.10mm ~ 0.44mm

Maximum Dimension: 220*1,500mm

Min PTH: 0.10mm

Min LW/LS: 2mil/2mil (0.5OZ)

Impedance control: Most popular values are 50 ohm, 90 ohm, 100 ohm, other values also available.