Flexible circuits are arguably the first instantiation of electronic interconnections. A flexible interconnection structure was first disclosed in patent literature by Albert Hansen—unearthed by gifted researcher, innovator, and self-described technology generalist Dr. Ken Gilleo1. The roots of flexible circuits, as determined by the patent Gilleo uncovered, date back to a 1903 British patent issued to Albert Hansen of Germany, entitled “Improvements in, or Connected with, Electric Cables and the Joining of Same.” The invention was designed to serve the new world of telephony and improve interconnection design.
Hansen was an amazingly prescient inventor who not only appears to have anticipated the flexible interconnections the industry relies so heavily on, but in a later disclosure, something that looks very much like a multilayer circuit of sorts. In the beginning, the flexibility of the circuit enabled the user to utilize all three dimensions of space to accomplish their design for interconnection needs. Today this continues to be an objective of all interconnections with 3D having become a watchword in electronic design at every level—from semiconductor chips and chip-lets to forklift installed systems—all of which take advantage of flexible circuit technology.
Since Hansen’s invention, a hallmark measure of flexible circuits is how they have become a ubiquitous chameleon-like technology for electronics, capable of adapting and facilitating the myriad changes required to build the dizzying array of electronic devices that have come to enhance and improve our lives—even as they increasingly invade life in general. Like a chameleon, these circuits largely stay out of sight and remain invisible to the user. We are not just surrounded and laden with electronics, we increasingly wear them as flexible circuits. We have even changed the way we refer to them, not as simply flex circuits but as flexible electronics and flex hybrid electronics.
While traditional flexible circuit technologies will likely continue to serve the needs of designers in established roles such as electrical and electronic cables, they are also enabling and pervading a fascinating range of new personal products. Note: The flex circuit technology getting ever greater use and attention these days was historically called polymer thick film technology (PTF). Polymer thick film is currently being rebranded as flexible electronics (FE) and flex hybrid electronics (FHE)2. Regardless, the printing of electronic conductors has been in the tool chest of circuit designers for nearly three quarters of a century. Once largely relegated to the production of PTF membrane switches, which serve nearly every imaginable type of electromechanical machine interface, the printing of conductors has been paired with a wide range of substrates because the printing and joining technologies used in manufacture do not require the high temperatures associated with soldering.
As well, for some time there have been semiconductor chips increasingly thinned to the point where they can be bent without fracturing, attached to the flexible base film, and interconnected directly to the circuits. This solution has been thoroughly embraced at NextFlex and it opens doors to products that can conform to the contours of the product being served, arguably in the same way that the chameleon adapts its appearance to mimic its surroundings. In that regard, most flexible circuits are “invisible,” hidden from the view of the user. We see this with electronic textiles, and I expect this trend to increase as more designers conceive of clever products to tempt consumers, whether for vanity, utility, or a combination. It may well be the addition of textile-based circuits that will allow clever designers to create adaptive, wearable camouflage for the military that helps keep future war fighters out of enemy sights. Now that would most definitely be a worthy demonstration of a flex circuit’s chameleon nature.
In summary, flexible circuits, regardless of the terminology used to describe them, are enabling an untold number of new products, performing their illusory magic flawlessly and unobtrusively. We can expect to see them (or not) in products long into the future.
- “The First 105 Years of Flexible Circuitry,” by Ken Gilleo.
- To learn more, I recommend reading “The Chip Shortage Leads to Innovation,” by Dr. Malcolm Thompson, NextFlex, September 2022, Design007 Magazine.
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. To read past columns or contact Fjelstad, click here. Download your free copy of Fjelstad’s book Flexible Circuit Technology, 4th Edition, and watch his in-depth workshop series “Flexible Circuit Technology.”
This column originally appeared in the October 2022 issue of Design007 Magazine.