Flexible circuits were introduced in a very limited way in the 1950s, but have not enjoyed the widespread use that its rigid cousin has. Although you will find flexible circuits in many consumer products today, including cellular telephones, laptop computers etc. they still make up only about 20% of the worldwide market for printed circuits.
Flexible circuits and rigid printed circuit boards have in common is that they both allow repeatable connections. Conductor routings in a flexible circuit are determined just like a rigid PC board by a single artwork, rather than by individual wirings.
Flexible circuits also allow extra-fine lines, as low as 2 mils on 4-mil centers, allowing high -density device population and reduced circuit size and weight.
Flexible circuits have one important advantage over rigid PC boards in that they give designers a third dimension with which to work. Flexible circuits can bend and shape around two or more planes during installation. They can solve space and weight problems by replacing several bulky boards with a single thin one. While in use, flexible circuits can also bend and flex up to 500 million times without a failure. This is something a rigid PC board simply cannot do.
Flexible circuits and rigid printed circuits are manufactured in much the same way. The materials are different to be sure, but the main processes are similar. The same print and etch methods used for printed circuit boards are also used to manufacture flexible circuits. Both begin with full coverage of copper and the unwanted areas are etched away from the pattern that was designed on your CAD system.
Both utilize plating to create through holes and via that allow multiple conductive layers. A note of caution however, flexible circuits are much more tedious at high layer counts than their rigid equivalent. Both circuits have insulation layers albeit different materials and processes. The point is, when it comes to electrical considerations, you can count on flexible circuits as well as you count on printed circuit boards.
Flexible circuits can be manufactured with the same copper thicknesses available for PCBs. Typical thicknesses used are ½ oz, 1 oz, 2 oz etc.
The calculations are the same as for printed circuit boards with the exception of dielectric constant and material thicknesses. We still must concern ourselves with trace width and thickness, space between traces, distance between layers, and dielectric constant. Once those calculations are made and confirmed the flexible circuit performs as well as a rigid PCB.
When faced with the design of a flexible circuit and its electrical characteristics it’s best to consult with GC Aero Flexible Circuitry. Remember though that the design in this respect will differ little from the expertise you already have as a printed circuit board designer.