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Embedded Intelligence
June 24, 2008 |Estimated reading time: 4 minutes
New technologies often take on an aura of inevitability, promising to revolutionize industries, either through obvious improvements from incumbent technology or sheer novelty. Once companies begin to evaluate these new technologies, some live up to expectations, and some turn out to be little more than hype. And some, despite proving their worth quantitatively, still struggle to catch on, often for complicated reasons.
One such technology, embedded passives, falls into this final category. The process of building passive components like capacitors and resistors into the circuit board itself, between interconnecting substrates, offers compelling advantages over placing those components on the surface. It frees space on the board surface, providing more room for additional functionality and opportunities for reducing the board's overall size. It helps suppress electromagnetic interference EMI radiation, and increases reliability by reducing the number of solder joints on the board. But so far, companies have been reluctant to take steps to fully adopt this new approach to board design.
IPC recently conducted a survey to assess the use of embedded passives in the printed circuit board industry. Committee members identified a number of challenges impeding embedded passive use. The biggest problem has been that the benefits of using embedded passives have been difficult to justify versus costs. John Andresakis, vice president of strategic technology for Hoosick Falls, N.Y.-based Oak-Mitsui Technologies, says "If [by using embedded passives] I now have some design flexibility where I can add additional functionality, I might be able to shrink the board, or I've just reduced my time to market by a month." But the problem is, he explains, "there's no set formula for those benefits."
Discrete Measures
Cost models that have been applied to traditional printed circuit boards using discrete components don't also apply to embedded passives. Dr. J. Lee Parker of JLP, in Mechanicsville, VA., says, "The models that I am aware of are very rudimentary." Parker, who worked in the interconnection laboratory at Bell Labs for 27 years, says that for companies to develop accurate analytical models to calculate the potential benefits of using embedded passives, someone has to do the research. "If someone is going to use buried capacitors, he or she has got to convince his boss that it's going to be a cost savings, and that's usually the rock that you hit that just sinks the ship. The only way you're going to do that is by doing some homework."
Parker says part of the problem is increased competition in the industry. "People have gotten very cost-sensitive in the past few years and they really don't want to do much homework, because that's going to be expensive, and if something's going to get in the way to the time to market that's also objectionable," he says. This competition has also made many companies reluctant to share their experiences with embedded passives, because the technology is still seen as a competitive advantage. This is likely to change as the economics associated with the technology spreads though, say both Andresakis and Parker.
Worth The Time?
Valerie St. Cyr from the Enabling Technology Group at Teradyne, Inc.in North Reading, MA., also cites the additional costs associated with building and testing boards with embedded components. For instance, she says, many board manufacturers will quote 15-20% tolerances for embedded resistors. To achieve higher accuracy, they have to be laser-trimmed before or after lamination or "build." "It's slow and it's expensive," she says. "Each one gets tested and trimmed off individually, as opposed to a mass production line of discrete resistors where they all come out exactly the way you want them. It's very time consuming and soon becomes a bottleneck process." This bottleneck can be broken, however, with enough demand. "It's a real chicken and egg situation," she says. "At some point, someone's going to want high volume and highly accurate resistors and they're going to have enough volume to cause an entrepreneur to develop a piece of equipment that will improve the throughput of automated laser testing. That will start to break one of the bottlenecks to greater implementation [of embedded passives]."
Design software developers are now starting to implement embedded passives modules, which should help manufacturers create more accurate designs from the outset. Andresakis says that in the past, designers developed workarounds to add embedded passives in their layouts, but now more tools explicitly address the requirements for modeling them. "There are definitely some better tools now," he says. "The software guys have realized that embedded passives is something that is coming, and so they have to address it."
Measuring Up
Will embedded passives live up to the hype? St. Cyr says it's a matter of finding the right applications. "High-reliability applications and consumer applications looking to reduce space and weight-those are going to be the two that push it," she says. Parker says that such demand, coupled with the assurance that the investment is worth it, will push embedded passives toward more widespread use. "What it boils down to is that somewhere, somebody needs to show that there is a good deal of potential that this idea will be cost effective," he says. "And then at that point I think you might be able to get the resources from OEMs and people like that to develop these tools."
Matt Wood is an IPC contributing editor. This article was originally published on the IPC Web site.