PCB expectors: The History of Flex PCBs

The History of Flex PCBs

At the beginning of the 20th century, early researchers in the burgeoning telephone industry saw the need to alternate layers of conductors and insulators to produce standardized, flexible electric circuits.

An English patent from 1903 describes coating paper with paraffin and laying flat metal conductors to provide the circuits. Around the same time, Thomas Edison’s notebooks suggested coating linen paper with cellulose gum, then tracing circuits on the gum with graphite powder.

The late 1940s brought in mass production techniques, resulting in a number of patents for photo-etching circuits on flexible substrate as a way of replacing wiring harnesses.

More recently, the addition of active as well as passive components to flexible circuits has introduced the term “flexible silicon technology,” referring to the ability to integrate semiconductors (using technologies that include thin-film transistors) onto the flexible substrate.

The combination of traditional advantages found within flexible circuit construction combined with onboard computing and sensing capability has led to exciting developments in several areas, most especially in applications in the aerospace, medical, and consumer-electronics fields.


Modern PCB manufacturers often face contradictory requirements when integrating complex circuits into a finished application.
The product needs to be light in weight, yet durable enough to survive in environments where heat, vibration and moving parts would tax traditional connections.

Additionally, manufacturing cost means that circuit integration cannot involve a lot of expensive, error-prone human assembly: it requires the repeatability and quality levels of IC design.

Finally, product lifecycles demand rapid prototyping and implementation, as time to market can make or break a product line. Flexible printed circuit boards (flex PCBs) offer advantages in all of these areas and can be used in a wide range of applications, from medical and aerospace to consumer electronics.

The Space, Weight, and Cost Savings of Flex

Redesigning a product to use flex PCBs rather than rigid PCBs deliver immediate benefits in weight. Customers commonly see weight reductions of up to 75% when compared to traditional designs.

This comes from using incredibly thin substrates made of polyester or polyimide material—films that can be as thin as 12-120 microns thick.

Conductive material traces are etched on the flex PCB, in as many layers as the PCB design requires. Typically, a coverlay is then applied to protect the layers from moisture, dirt and damage.

One important use of flex PCB design is the replacement of wiring harnesses and ribbon connectors once used to link together different boards—for example, to connect the engine control unit in an automobile to the dashboard or lighting components.

The standardization and economy of scale that goes along with this also reduces assembly cost by reducing the number of components and interconnections, and allowing for high-quality mass production.

Many flex PCB users find that they can reduce the cost of connections by up to 70% versus traditional wiring harness construction.
And with the reduction in connection cost comes a reduction in costs associated with inconsistent quality—flex PCB’s standardized construction also eliminates the source of potential errors from hand-built harnesses.