The LED Film, also called LED embedded film or LED lighting film is a thin and flexible electronic circuit with surface mounted light emitting diodes on the polymeric film. One type of conductive material may consist of transparent conductive films[1],[2]:
Because industrial IPC-T-50 "Terms and Definitions for Printed Boards" are defining a flexible circuit as "A patterned arrangement of printed wiring utilizing flexible base material with or without flexible cover layers.", this definition cannot be applied to the transparent type of flexible circuits, which will contain no printed wiring, in fact no wiring at all.
Basematerials for non transparent LED Films are usually based on thermally stable materials, like PEN or Polyimide to enable reflow soldering pastes to sinter at temperatures exceeding 220 °C. In the case of Polyimide and PEN the conductive paths will be printed to the base materials mentioned above.
To enable transparent conductivity, the other solution consist of laser patterning transparent conducive material, which was vacuum sputtered on the base material, for example on highly transparent Polyester. Polyester may not be sintered, in fact it will lose its flatness at temperatures exceeding 80 °C. Consequently the pick & place process must be done at low temperatures using appropriate heat free curing pastes. These paste may consist of metall powders filled lacquers, which will dry for example. Or they may consist of metall powders filled 2 component glues, like epoxy resins.
Transparent conductive LEDFilms[3] are used for standard LED glass , transparent LED glass, for automotive LED composites[4], or for laminated films between other materials like PVC, metals, polymers, stones, or natural materials like wood.