(This column, which originally appeared in Global SMT & Packaging magazine 6.9 (October 2006), is also available as a free PDF.)

Printed circuits are a fundamental element part of virtually all electronic assemblies and have been since their origins. The moniker ‘printed circuit’ appears to have first come into broad use in the mid 1940s. It was an accurate description of the techniques used at the time to create these, then new, interconnection devices. It remains an apt term today. However, because in the early going many printed circuits were actually created by printing conductive inks directly on to insulating substrates using screen printing technologies, the term was especially apropos. Moreover, in those early days the same printing methods were often used to print passive devices, most often resistors. Capacitors, however, were a recognized option.

Today, printing technology, in one form or another, is still used to produce printed circuits; however, the number of different ways that printing has been adapted to the printed circuit manufacturing process is quite impressive. Also changed over the years have been the ways that technologies that support or augment the printing process have been adapted to the changing and evolving role of the printing process over time. For example, early imaging processes involved the direct screen printing of conductors, then conductive inks gave way to screen printing of etch resist. After that, screen printed etch resists gave way to resists that could be imaged and developed and it now appears that evolution is going full circle as the industry is poised for yet another step forward, this time back into the past of printed conductors, but with some significant technological twists.

Figure 1: Two methods of directly printing circuits. In the upper image circuit patterns of conductive ink are patterned on to a web of material which is moving. In the lower image is shown a print and plate method using a catalytic ink and a plating bath.

Though there will be much in common with the earlier direct printing of conductors, the nascent era of next generation printed electronics will not look much like the earlier screen printed technologies. Instead, the new era will be marked by the adaptation of methods more familiar to the creation of the printed word than the ancestral printed circuit methods these new methods are poised to replace. As the interconnection industry moves toward the next generation of printed circuits, we may well see not only time honored printing methods such as gravure and offset printing but also printing methods based on ubiquitous laser and ink-jet printing technologies that currently flood the market. These widely used printing methods may well be on they way to stepping in as replacements more the more familiar photolithographic methods used for manufacture of today’s printed circuits. Both the new and the old technologies will likely employ a variety of advanced generation inks including conductive organic polymer inks, metallic inks comprised of nanotechnology metal powders and even catalytic inks onto which metals (mainly copper) can be reduced and plated with additional metal to a chosen thickness. As evidence that things seem to go in circles, a variation of the latter concept of printing catalytic inks, was actually looked at over 15 years ago1. These two approaches are illustrated in Figure 1. Other next generation inks will offer adjunctive capability including inks for insulators, resistors and it appears, even semiconductor materials. The combination of all of these inks should make it possible to create true printed circuits in the truest sense of the term as opposed to the ‘simple’ electrical interconnection structures being fabricated today. 

What has been driving the idea of printed electronics is the promise it holds, not only in terms of the potential manufacturing economies it might offer, but also in terms of the many new types of products that might be made possible when it is deployed and the processes and materials fully shaken out. As a continuous web based manufacturing process, certain deployments of the technology, such as direct right ink and insulator technology offerings, could provide a significant potential for reducing both product cost and time to market. For example, because data being printed is simply the product of the presence or absence of dots of chosen material which is raster printed onto a passing substrate, it becomes very clear that it will be possible, with the absence of image masks, to economically build a product with a run unit of one. This is possible because one can, during the middle of a production run, create a separate and completely different circuit. One only needs to leave the required space open and available.

The first products likely to benefit from such processing include RFID tags, different types of lighting and various displays including LED and OLED1. The latter two items may prove most interesting because they would be enabled by the technology’s ability to print semiconductor materials and thus transistors. Following on that line, other suggested candidates include solar power applications and even logic and memory3. Displays seem to be a ‘natural’ and an number of industry watchers suggest that it will be the advent of printed electronics that will truly open the ‘e-paper’ market. Looking at the scope of the opportunity, it has been suggested that the potential market for all types of printed electronics will be quite large. For example, technology market research firm, IDTechEx, suggests that the printed electronics market could reach 96 billion USD4 in the year 2020. In an industry that has seen large projections for nascent technologies come and go in the past, a number that large might want to be taken with a grain salt, but even if short by an order of magnitude, it is still are quite respectable market. The future will be the ultimate judge of the projection’s accuracy.

To sum up, it appears that printed electronics are now on their way and could well be gaining momentum as supporting technologies including, machines, materials and printing processes are rung out and implemented. Printing electronics is clearly a very attractive concept today, just as it was when early developers first had the notion that it could be done. However time and technology have improved and the new methods should open the door to the manufacture and purchase of not only more cost effective electronics but also should allow the customer to cost effectively purchase the most precious commodity of all and that is time.

References
1  US Patent No. 5,250,758
2  http://www.pbs.org/cringely/pulpit/pulpit20040805.html
3 http://www.azom.com/details.asp?newsID=200
4 http://www.idtechex.com/products/en/view.asp?publicationid=117

Keywords : Joe fjelstad, Fjelstad

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