CircuiTree - February 2009 - (Page 19)

Flexible Thinking By Joe Fjelstad What’s Ahead for Flex Circuits? A s this month’s column is being written, the world is in a deﬁnite economic recession and possibly headed toward a depression. Things have been worse economically in the past around the globe but not in the lifetimes of most of the planet’s current residents. The situation is troubling but still it is not as bad as it was three–quarters of a century ago during the Great Depression when unemployment in the U.S. was 25 to 30 percent. Fortunately, as the familiar saying goes, “Tough times don’t last but tough people do,” and the same holds true for many technologies, including ﬂexible circuit technology. Thus, in these dreary times, we must look ahead to the promise of the future and plan for the better times that are sure to come as certainly as day follows night (if I may be so bold as to reverse the sequence, originally scribed by Shakespeare, to reﬂect a more positive order). The myth of the phoenix came to mind while pondering what might be next for the ﬂex circuit industry. The phoenix is a mythical bird having a multi-century lifecycle. As it nears its end, the phoenix builds itself a nest that it then causes to ignite and the bird is reduced to ashes, from which a newborn phoenix arises to live again and repeat the cycle. History is also cyclic. Philosopher George Santayana warned that those who will not learn from history are destined to repeat it, so it is not unreasonable to expect that we too will rise from the ashes of the present time to a new and, hopefully, brighter future in the years ahead. What might the ﬂex circuit industry look like in those coming years? My crystal ball works no better than any other fortune teller, so I can’t offer guarantees about my prognostications. On that topic, baseball hall of famer Yogi Berra said it best: “It’s hard to make predictions, especially about the future.” With that in mind, it can be said with fair certainty that the technological vector of ﬂexible circuit technology will be at least somewhat similar to what it is today. This is suggested in recognition of technology guru, historian, and futurist Ken Gilleo, who identiﬁed that the ﬂex circuit has technological roots dating back to 1903. Thus, the suggestion of some degree of technological stasis for ﬂex circuits seems to have some validity. After all, how many variations on a theme of conductors on a ﬂexible base material can there be? Actually, the answer to that question is that the number can be quite signiﬁcant. The truth is that while there are presently only a couple of ﬂexible base materials in broad usage—polyimide and polyester— there are many other possibilities. Polyester, at present, is commonly used for relatively simple circuits that do not require soldering, and there are many applications in that number. The ubiquitous membrane switch is a prime example. There are a few different formulations of polyester, each with slightly different properties. On the other hand, polyimide, though more expensive, is used for the vast majority of ﬂex circuit designs. Polyimide is widely popular due in large part to its higher temperature capabilities that allow it to withstand not just tinlead solders but the new high-temperature lead-free solders as well. As with polyester, there are number of variations on the polyimide theme, in terms of formulation, that allow for the creation of a fairly wide range of properties in terms of everything from dielectric constant and dissipation factor to moisture absorption characteristics (which impacts dissipation factor) and coefﬁcient of thermal expansion, all of which are important factors in ﬂex design and use. With these materials well in control of the present, what might be next? Given the challenges of ﬂex circuit assembly and cleaning as component lead pitches continue to drop, one possibility is the implementation of a reverse assembly process, where standard packaged electronic components are encapsulated in a ﬂexible base material and the circuits are plated on top of the component terminations. This would greatly reduce processing steps and, as a direct result, cost. Equally important is that the elimination of soldering holds out the promise of a much more reliable assembly through the reduction in the number of interconnections, especially when it has been shown time and again that solder joint failure is the most common mode of failure for electronic assemblies. One of the more attractive features of such an approach is that it opens the door to the potential use of a broad range of new and old thermoplastic materials, most, if not all, of which could be potentially recycled in the manufacturing facility, thus minimizing waste. The reason for the broader potential range is that the soldering process would be bypassed. Another promising aspect of the concept is that it leaves open the door for processing ﬂexible circuits as if they were rigid boards. This concept is made possible by creating a circuit panel with embedded components, processing it as if it were a standard rigid PCB and then milling away the areas where ﬂexibility is desired. A chemical or thermal polish of the rigid to ﬂex transition areas would obviate concerns over stress risers and crack propagation. It is a promising concept that could allow the ﬂex industry to continue its drive to lower cost and higher performance. In summary, all technologies have ancestors, lifetimes of their own, and, ultimately, if they are ﬁt, progeny as well. The descendent technologies are generally better and more robust in a Darwinian fashion, even if only incrementally so. We can expect that trend will continue in the future. ■ Joseph Fjelstad, founder and president of Verdant Electronics and co-founder of SiliconPipe, is an author and innovator in electronic interconnection and packaging technologies. Download his flex circuit book free at www.flexiblecircuittechnology.com. E-mail: jfjelstad@siliconpipe.com circuitree.com • February 2009 19 http://www.flexiblecircuittechnology.com http://www.circuitree.com

Table of Contents Feed for the Digital Edition of CircuiTree - February 2009

CircuiTree - February 2009 Contents Lead Wire The Wire Tech Talk Flexible Thinking Are Better PCB Design Tools and Manufacturing Enough to Stay Competitive? The Strategist Fein-Lines The Big Deal Over Fine Pitch Assembly Asian Section View From the Middle Market Outlook Technical Product Spotlights Classified Ads Upcoming Events Ad Index

CircuiTree - February 2009

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