Section: news

Washington - Flexible circuit-board technology-once an obscure, arcane packaging option- is being propelled into the design-engineering mainstream.

Driving the new twist is a surge in demand from myriad space-conscious applications at the leading edge of svelte new packaging designs in portable and mobile-computer, communications, and automotive applications.

Many observers at the recent Institute for Interconnecting and Packaging Electronic Circuits' Technology Marketing Research Council (TMRC) meetings here believe the surge marks a coming of age for the technology, which is seeing use in areas that demand thinness, such as PCMCIA cards above all else. Domestic flexible-circuit-board shipments rose sharply last year after several years of flat growth.

Flexible boards were expected to see dramatic growth when portable computers first started appearing, but the technology didn't grow much beyond becoming the link between notebook motherboards and displays. Now, many companies are finding new applications for very thin circuit boards.

"We're now entering a renaissance. We're seeing a lot more users for flex in innovative and value-added applications, not just historical uses like disk drives and printers," said Happy Holden, technical contributor for Hewlett-Packard's Printed Circuit Organization, (Loveland, Colo.). "We see very large growth for flex. We're designing it in as fast as we can digest the technology. A lot of people want flex, but they don't know how to design it in."

Much interest

Vendors say that OEMs are driving the high level of interest in a marked change from the past, when the makers of flexible circuits often spent months trying to convince system designers that flexible circuits would fill their needs.

"We're seeing a lot more requests in new areas such as medical and automotive," said Karen Carpenter, marketing manager at IBM Microelectronics (Endicott, N.Y.). "In automotive, they want circuits they can wrap around the tight spaces under the dash. In medical, they want thin, lightweight boards that can go inside the body."

PCMCIA cards helped spark the interest. When it became apparent a few years ago that PCMCIA cards would become a huge market, many designers started to look at flex circuits when they realized how difficult it would be for board makers to make multilayer Type I cards.

"Thin is in," said Dieter Bergman, technical director at the Institute for Interconnecting and Packaging Electronic Circuits (IPC; Lincolnwood, Ill.). "PCMCIA started coming out, and everyone said they needed thin materials. The boards still need a lot of interconnection capability, a lot of layers. Now, everyone is looking at thin materials."

Flexible circuits are made using entirely different technology than rigid boards. Copper circuitry is put on thin sheets of polyimide or polyester. Material vendors such as DuPont, which makes Kapton and other materials commonly used in flex circuits, agree that growth is rising rapidly.

"What's happened recently that makes flex appear to have a high growth rate is that the U.S. has seen a period of flat growth. Now it's back on a historical growth curve or better," said Stephen Simpson, substrate systems market manager at Du-Pont High Performance Films (Circleville, Ohio). "What makes it especially exciting now is that rigid-board applications are being penetrated at a rate we've never seen before. Until now, flex has always grown only in its own markets."

While growth in the United States is seeing a sharp rise (see chart), domestic production is still far smaller than the Japanese production. The IPC estimates that Japan owns 49 percent of the $1.6 billion worldwide market. U.S. vendors have only 29 percent of the market.

That has prompted U.S. consortia to move to get new technologies into production. Executives note that flex is capable of higher line densities than rigid boards, so it is critical for U.S. manufacturers to stay competitive in the technology. Sheldahl (Northfield, Minn.) has devised a new technique that has attracted Arpa funding and recently got additional support from another group.

"One advantage to flex is that it's easier to make fine lines," said Marshall Andrews, president of the Interconnection Technology Research Institute (ITRI; Austin, Texas). "That's the thrust of a new program we have with Sheldahl. We have four companies that are processing new materials developed by Sheldahl. After they finish their manufacturing runs, they will share their experience with Sheldahl so they can move the technology into the market. If the technology has benefits, we want to implement it quickly, not to let our competition get their first."

Small segment

Despite all the interest in flex, it still represents a small segment of the overall market. The meetings of the TMRC, which tracks the shipment levels of circuit boards for the IPC, revealed new figures that show that the $70 million flex market is greatly overshadowed by the $39 billion market for rigid boards. Though flex is small, it is growing quickly, with much more interest than in recent years.

"We got about 80 people here at our flex session," said Kim Sterling, director of market research and education at the IPC. "Two years ago, we were happy to get 20. The interest is coming from OEM designers who are looking for ways to shrink their products. We have also started two new flexible conferences that have gotten a lot of interest."

Today, very few makers of rigid boards have flexible-circuit capabilities. But as rigid boards move to thinner layers, they are starting to pay more attention to the way that flexible boards are manufactured.

"Inner layers are so thin, they're almost like flex," said Thom Dammrich, executive director at the IPC. "Rigid-board manufacturers are interested in learning how to handle flex."

However, there's some skepticism about whether the two technologies are similar enough for manufacturers to blend one technology with the other. While some of the handling issues are similar, the two manufacturing operations might be so distinct that board makers won't be able to make or market flex without setting up dedicated operations.

"I think it will be very hard for rigid-board manufacturers to do flex-it's such a different technology," Sterling said. "It can take a flex manufacturer two days to deliver a quote, because the technology is so customer-specific."

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By Terry Costlow