With the development of electronic devices towards miniaturization and portability, the assembly of electronic devices is becoming increasingly intensive. Flexible circuit boards, due to their small size, light weight, and high circuit density, have gradually replaced the role of traditional wires in the assembly of electronic devices. In recent years, the market share of flexible circuit boards (FPCs) in printed circuit boards (PCBs) has increased from less than 10% to over 20%, which also proves the development of FPC market demand.

FPC, as a connecting wire in electronic devices, mainly plays a role in conducting current and transmitting signals. When the signal transmission line is distributed at the outermost layer of the FPC, in order to avoid signal distortion caused by electromagnetic interference during the signal transmission process, the FPC will press a conductive layer (electromagnetic shielding film) after pressing the covering film, which plays a role in shielding the external electromagnetic interference. The most common one is the FPC used for image signal transmission in digital cameras. As a transmission line, FPC usually has special impedance requirements, but the FPC structure changes after pressing the electromagnetic shielding film, and its impedance calculation method also needs to be modified. Therefore, this article studies the impedance changes after FPC pressing electromagnetic shielding film, corrects its impedance calculation method, and provides reference for the design of FPC pressing electromagnetic shielding engineering.

Experimental design

1. Test materials

PI based adhesive free sheet: PI thickness 2 mils, copper thickness 0.5/0.5 OZ;

Cover film: PI thickness 0.5-2 mils, adhesive thickness 25-35 μ M;

Electromagnetic shielding film: conductive adhesive thickness 10 um, PI thickness 6-10 μ M.

Testing and testing equipment and conditions

Fast press, network analyzer.