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Flexible Thinking: Flexible Circuits or Flexible Electronics?

The term “flexible circuit” has been ensconced and accepted in electronic interconnection technology lexicon for several decades. In broad brush strokes the term has embraced every type of printed circuit produced on flexible base materials, regardless of the nature of the conductors used: metals, such as copper; or conductive inks, such as silver or other conductive particle filled polymers. The latter type of truly printed circuits, have, for many years, been referred to as “polymer thick film” circuits. Their predecessors were described in a Government Printing Office booklet published in 1947, titled “Printed Circuit Techniques.” These circuits were easy and inexpensive to produce and were (and still are) commonly used to create membrane switch circuits for appliances and keyboards for every imaginable type of electronic product. Often, simple components were attached to these polymer and metal powder circuits using conductive adhesives to add function and versatility to the end-product while keeping costs low.

For many years, flexible circuits have also been designed to have components attached and integrated into what is called a flexible circuit assembly. In earlier years, flexible circuits played more limited roles as a means of providing a flexible link for conductors between rigid printed circuits or rigid PCBs and connectors. In the 1960s, the flexible circuit was integrated into a rigid printed circuit board by the visionary pioneering engineers at Sanders Associates in New Hampshire, yielding a product now commonly known and referred to as a rigid-flex circuit.

These terms were, and still are baseline, fundamental, widely understood, accepted by those in industry, and have been standardized. Standards were written to help codify issues related to flex circuit design, the materials used, as well as their manufacture, assembly, and performance. The IPC still leads that effort. As I have said in the past, I personally see standards as a sort of “industrial strength glue,” if you will, that serves to hold the industry together and set expectations for product design, production, and performance.

In 2015, NextFlex, an American consortium of electronics companies, academic institutions, and various nonprofits, along with several state, local, and federal government partners, was created. The group’s self-reported charter was to promote what was historically known as printed flexible circuit technology. However, the founders decided, for reasons unknown, to form under a new name, “flexible electronics.” It is arguable that such a new name was not really needed but it began the marketing of flex circuit technology under the new name, and in truth, it did help to bring flexible circuit technology into the sights of more people both in the industry and the general public.

The marketers did so with great determination, even to the point of changing the title of the content for flexible circuits found on Wikipedia from “flexible circuits” to “flexible electronics.” That remains the case to this day—type the term “flexible circuits” into the search space on Wikipedia and view the results. As someone who deeply respects history and intellectual integrity, it seems an uncalled-for misappropriation of an accepted and decades long-established historical term and by doing so creating unnecessary confusion, as the product is still by original definition a flexible circuit. The term flexible electronics has since morphed to include “flexible hybrid electronics” (FHE) which involves the integration or assembly of active and passive devices.

To the credit of the newly formed community (which also includes SEMI’s FlexTech), they have done good service to the electronic interconnection industry as evangelists for flexible circuits by attracting educators and academic technologists, encouraging them to envision and devise new ways to integrate flexible and stretchable circuits into next generation products of every imaginable type, especially wearable electronic devices. They have risen to the challenge as the variety of applications has continued to grow and, through the providing of a government sponsored environment, to explore those ideas. With the shared goal of advancing U.S. manufacturing of printed flexible electronics, the two entities have been promoting flexible circuit technology to the benefit of the entire flex circuit industry by raising awareness of the many benefits that flex circuits provide.

Since their launch under an Air Force Research Labs Cooperative Agreement, the NextFlex and FlexTech communities of technologists, educators, problem solvers, and manufacturers have come together to collectively facilitate the advancement of flexible interconnection technologies innovation by providing a space for shared research and material, process, and equipment development. It also serves as a training space for local students. 

The long-established global and growing flexible circuit community will continue to thrive as increasing numbers of electronic product developers become aware of their potential to solve interconnection challenges. Flexible circuits, by any other name, will continue to be there to help make it happen just as the venerable technology has done since its inception many decades ago.

For those with interest in reading more on printing technologies for flex circuits, Chapter 11 in Flexible Circuit Technology 4^th Edition (a free I-007eBook available for download) details the long history of the “new” technology of printed electronics. The chapter includes a review of traditional printing technologies such as screen printing, rotogravure printing, flexographic printing, and offset printing, as well as inkjet options.  

Joe Fjelstad is founder and CEO of Verdant Electronics and an international authority and innovator in the field of electronic interconnection and packaging technologies with more than 185 patents issued or pending. Download your copy of Fjelstad’s book Flexible Circuit Technology, 4th Edition, and watch his in-depth workshop series, “Flexible Circuit Technology.”