MEMS Packaging - The Saga Continues

The symposium drew a truly international crowd with attendees from Germany, Romania, The Netherlands, France, Italy and several companies in Asia added to the usual US contingent. Some of the speakers at this conference offered insights into the changing and challenging world of MEMS.

Most analysts agree that MEMS based products are forecasted to grow significantly in the next ten years. We asked our experts what they thought the driving factors are for that growth. Most agree that one of the largest reasons for this growth will be new applications.

Tom Clifford of Lockheed Martin Space Systems was a speaker in the End User Applications session of the symposium. He believes that, "MEMS growth depends on the product and the corresponding process. There are scores of current and potential MEMS applications of all sorts. Success depends on the profoundly new capabilities that well-designed and positioned MEMS products will provide."

Mathieu Potin is a Market Analyst for YOLE Développement out of Lyon, France and presented in the Industry and Market Overview session of the symposium. Potin believes growth of the MEMS market goes beyond just new applications. "The development of the MEMS markets will of course be related to new applications," explained Potin, "but the primary market growth would depend on the ability of MEMS manufacturers to supply from the component to the module." Potin's definition of a module is a MEMS product which can provide a function instead of just a sensor (component) alone. Potin believes that device manufacturers will be pushing a module offer (compared to a component offer) in order to attract added value.

Many MEMS based products such as DLP, accelerometers, pressure sensors and printers, can already be found in the general marketplace. With the introduction of so many new applications we should expect to see many other products in the near future.

"MEMS microphones are a major growth area for applications such as hearing aids and cell phones," according to John Heck of Intel. "RF MEMS switches are entering the marketplace, starting in test and measurement equipment, and we may expect to see them in handheld wireless devices within the next few years. Also a wide variety of medical devices will be seen in the near future." Heck was the Session Chair for the Enabling Technologies session.

Mark Crockett of Applied Materials said that people should expect to see MEMS sensors and actuators in more "user-centric" devices like set top boxes that sense viewer's emotions and adapt accordingly. "We may also begin to see wearable devices to optimize worker productivity and effectiveness," said Crockett, who presented in the SEMI Standards Workshop on the second day of the symposium.

Potin added that, "Micro fuel cells are at a key development stage in Japan with companies like NEC, Fujitsu, and Toshiba, and are likely to enter the cell phone market in 2007-2008. Several service providers including NTT and KDDI have already presented mobile phone models with integrated micro fuel cells. Europe and the US are also engaged in such development through companies such as STM and Infineon."

Alvin Barlian, of Stanford University, believes that as the MEMS field matures, more development of MEMS products will be driven by academic and industrial labs. According to Barlian, relatively newer applications may include biological and chemical sensing for military and homeland security as well as transportation infrastructure systems, structural health, and environmental monitoring. The rebirth of aerospace and telecommunication industries will also increase the demand for more advanced MEMS products. In addition, advances in material science play a major role in the growth of MEMS by enabling innovative unconventional fabrication processes. Barlian was a speaker in the Academic Workshop which was part of the second day of the symposium.

Other than new applications, cost reduction and increased reliability still remain critical drivers for growth in the MEMS industry. Heck feels that significant competition in the foundry business, as well as common availability of MEMS-specific tools such as wafer bonders and deep silicon etchers are key to lowering costs.

"Lower costs and improved reliability will encourage the expansion of MEMS into new markets," added John Crane. "As improved assembly processes yield lower costs and better reliability, new markets will proliferate." Crane represents Boschman Technology who presented in the Advanced MEMS Packaging Trends session.

Ken Yang of Honeywell believes the growth will be driven, not only by lower cost and better performance, but also by ease of manufacturing and government policy requirements. Yang was a speaker in the Advanced MEMS Packaging Trends session.

Clifford agreed that cost and reliability aren't the only issues, saying that, "Most MEMS concepts must confront and control particulate and molecular contamination. Furthermore, specific challenges include CTE mismatch and thermal management; pass-thru of optics / gases / liquids / signals; vacuum packaging; and subtle but crucial materials compatibilities. "

For people who have been watching the MEMS market for many years, it seems that changes have come slowly. However, some significant changes have occurred over the past year according to our experts. Heck explained, "MEMS foundry consolidation has started to occur, and this trend will likely continue. Also, many groups are at the cusp of commercializing in-situ, or self-packaging methods for MEMS, where the mechanical elements are self-sealed during the fabrication process. This enables the MEMS die to be treated much like a standard IC throughout the packaging process, thereby reducing packaging cost significantly."

Clifford believes many things are changing for MEMS. "Certainly one enabler is maturing design software keyed to multi-physics solutions and to the particular fab process," explained Clifford. "Another is growing materials expertise, riding on nano-lab developments. Another enabler might be turn-key development services structured to ease and accelerate the painful transition from concept to manufacturable prototype. Another bright light is the emergence of ‘packaging' in academia, as a respected and pivotal skill-set."

As new MEMS devices are developed, the packaging industry will continue to struggle with the question of whether to use existing technology or develop new technology. This question becomes even more important when getting MEMS products into high volume. Many people are divided on this. Heck believes that current packaging solutions will continue to evolve and drive down cost, but also new packaging methods will begin to arrive in commercially-available products in the near future. "In order to get to high volume production," explained Heck, "ultralow cost packaging methods are needed, both in the form of cost reduction on existing methods (such as glass frit wafer bonding), and the advent of new self-sealed MEMS devices, which will enable significant cost reduction."

Clifford agreed that both existing and new technology will be needed depending on the product. "Some, including hermitic fluidics, optics, integrated sensors, etc. might currently be package-limited. Others might work fine in tailored conventional or vacuum-finessed packages. In every case, the package is a major challenge."

But many people, like Chris Lee of Quantum Leap Packaging, feel that existing packaging must be made to work in order to keep costs low. To this end, according to Lee, companies like Quantum Leap are combining existing packaging technology with new material sets such as QLP's QuantechTM high performance polymer material to meet the changing demands. "As MEMS devices become more complex," explained Lee, "devices are much more stress sensitive and prone to lower performance yields. Managing the device stress is a key in packaging in high volume." Quantum Leap Packaging presented in the Enabling Technologies session.

Crane added, "As MEMS products have migrated from ceramic packages to BGA and/or QFN package types, the ability to move to high volume production has become easier and easier."

One of the biggest questions for packaging MEMS has always been and continues to be, where is the packaging done, in the front-end or the back-end? Both sectors are working on new packaging technology which will enable the proliferation of MEMS.

"In-situ packaging is beginning to pay off," according to Heck. "This technology comes directly from the front-end fabrication side."

Yang agreed that wafer level packaging and wafer level vacuum packaging done at the frontend are critical to move MEMS forward.

Crane believes that the ability to successfully mold exposed die MEMS, such as finger print sensors or optical sensors, using transfer molding and film assisted molding, has allowed for significant assembly cost savings and improved capability. Film assisted molded products are free of mold compound flash and bleed. Lower cost and a reliable process at the back-end have enabled such MEMS devices to proliferate.

There are other areas of concern for MEMS beyond packaging. One of these is Intellectual Property. With the increasing trend toward overseas manufacturing in the past few years, IP has become a critical issue in all semiconductor areas and perhaps more so for MEMS products. Clifford believes IP is a bigger problem for MEMS. He explained, "IP resides in and must accommodate the one fact that characterizes all MEMS products: the inseparable linkage of design / process / material / fab tooling / test methodologies / process techniques /etc. Any IP and business arrangement (licensing, scale-up, product proliferation, supply-chain expansion, etc) must deal with that."

Heck agreed saying, "MEMS devices are so much more process-dependent than IC's - you can easily port a new CMOS design from one foundry to another. But the IP inherent in a MEMS device is in both the design AND the process. Therefore foundries and companies may possess key differentiators based on processes they develop."

Another area of concern for MEMS is standardization. This year's MEPTEC conference was extended to two days to include a half-day workshop, in conjunction with SEMI, to discuss standardization for MEMS. MEMS offers a unique challenge when it comes to standardization because so many of the devices are applications specific. "Applications that are customized, generally require greater up front cost to achieve economies of scale," explained Crockett.

"Standardization and level of difficulty will be driven by a variety of market forces. Unique applications will only leverage standardized solutions if the standards exist. Today, such standards for MEMS are not an option. As individual solutions proliferate, advantages in standardized solutions grow. For example, if five products perform the same function to a customer and only one of those products offers features in compatibility and lower cost of ownership through standardization, then the decision of which product to buy is simple. Establishing this differentiation is critical in newly shaped markets."

Heck believes that because MEMS devices are all made for different purposes and in different markets, standardization will only work at a very basic level. "We already have several relatively standard process modules for MEMS. For example, glass frit wafer bonding is so common these days that it may be considered a standard; this is in part due to the availability of wafer bonding and screen printing tools. I don't think we will ever see full processes that are standard in the sense that many devices with different functions can be made with a single MEMS process."

Though it may be difficult, standardization is still important, even with application specific MEMS products, according to Yang. "At least individual processes should be standardized so that you can use any subset of them to apply to your specific process set. It can then enable the foundry to group similar processes together to make a volume production from various products."

The half-day workshop had some good results. According to Bettina Weiss of SEMI, a new working group on hermeticity was formed, which will meet for the first time at SEMICON West in July. Depending on the findings of this new group, it is expected that at least one new SEMI Standard will be proposed in the general context of hermeticity. With or without standardization, the MEMS market continues to grow. According to Marlene Bourne of Bourne Research, funding of MEMS start-ups exceeded $500 million in 2005, with the average funding received per round at approximately $13 million. Bance Hom of Consultech International and Symposium Co-Chair said, "MEMS start-ups today are more market driven rather than technology driven...more direct application now, rather than pie in the sky fantasy we may have seen in the past." One thing is for certain, even with all the issues and challenges facing MEMS, the technology is here to stay and getting stronger every day.