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64 DESIGN007 MAGAZINE I FEBRUARY 2025 erature searches of my dear friend Dr. Ken Gilleo) date back to the early 1900s but the technology did not find significant commer- cial use until the 1960s and 1970s, primarily in militar y and aerospace applications, but also notably in automotive dashboard instru- ment display cluster circuits. Typically, early flexible circuits were relatively simple, single- layer designs made from polyimide or poly- ester films, used in applications that required flexibility but not necessarily high-density interconnects or sophisticated features. However, as demand for smaller, lighter, and more versatile electronics grew, so too did the potential for flexible circuit technology. Today, flexible circuits are oen multilayer and ubiq- uitous in modern electronics, from consumer gadgets like smartphones and wearables to advanced medical devices, automotive sen- sors, and industrial control systems. e chal- lenge over the past few decades has been to make flexible circuits more robust, capable, and cost-effective, while maintaining their inherent flexibility. e last few years have seen significant strides in achieving these goals. The Role of Materials and Processes One of the most significant recent advances in flexible circuit technology has been the devel- opment of new materials. Traditional flexible circuits were limited by the availabil- ity of suitable substrates and conductors. Polyimide and polyester films dominated as substrates, while copper was typically used for conduc- tors. While suitable for many applications, these materials had limitations in terms of conductivity, durability, and manufacturing complexity. In recent years, there has been a concerted effort to develop materials that overcome these chal- lenges. Among the most exciting develop- ments have been improvements in conductive inks and printing technologies. Researchers in both industry and academia have made sub- stantial progress in developing highly conduc- tive inks: not only silver, which has long been the go-to solution, but also improved copper and more recently, graphene. ese improved inks, in combination with advances in print- ing technologies, allow for the creation of intricate circuit patterns with a lower cost and faster turnaround time compared to traditional methods. e concepts now being offered har- ken back in my memory to the ELF Technolo- gies founded by Raychem scientists Dr. Leo Svendsen, Dr. Gary Geschwind, and Ray Noel, whom I helped as a consultant to launch the company in Redwood City in 1990. At ELF (an acronym for Extend Length Flex), we were laser-printing catalytic toners onto moving rolls of polyimide film and then elec- trolessly and electrolytically plating them with copper in a roll-to-roll process. At the time, I envisioned an objective to create an "economic run unit of one," a "holy grail" of manufacturing. I suggested that it might also be possible to have a factory (initially limited to single-sided flex) run virtually by the customer where they bid for position in a production cue. Current print- ing technologies not only shorten time to pro- totypes and market but also make flexible circuits more affordable. Moreover, they enable the design of circuits with complex geometries that would be difficult or impos- sible to achieve using more conventional manufacturing techniques. at said, there is another potential companion method that might be used: laser direct structuring (LDS), which uses a laser to directly structure conductive pat- terns onto a substrate by ablating copper metal rather than imaging with a photopolymer and " One of the most significant recent advances in flexible circuit technology has been the development of new materials. "