Double Layer Flex PCB  //  Overview

Double-sided flex circuits consists of double-sided copper clad material with top and bottom cover films (PI or Green/Yellow Oil, Carbon Ink, etc).  Two conductive layers with an insulating layer between, plus conver layers on outer layer.

The cover films are pre-routed to access copper from both sides using plated thru holes(PTH). Theses flex circuits can be fabricated with or without plated through holes, though the plated through hole variation is much more common. 

Because of the plated through hole, terminations for electronic components are provided for on both sides of the circuit, thus allowing components to be placed on either side. Depending on design requirements, double-sided flex circuits can be fabricated with protective coverlayers on one, both or neither side of the completed circuit but are most commonly produced with the protective layer on both sides.