Embedded components: a new development? It's an old technology, but the potential for revolution remains.

One hot topic in semiconductor packaging and assembly is embedded components in the IC package substrate or PCB. What are these structures? And is this a new concept, or is the technology finally moving closer to production after years in R & D?

What's an embedded component? IC packages with embedded active or passive components are structures on which the substrate is fabricated on top of the active device and may incorporate resistors, capacitors or inductors. Embedded components in PCBs feature active or passive devices incorporated into internal layers. In this embodiment, embedded passives provide an alternative to issues associated with discrete parts, including cost, handling, assembly time and yield, and board space.

General Electric introduced the "chips first" concept more than two decades ago. Companies including ACET in Taiwan, Casio Micronics in Japan, and Freescale Semiconductor in the U.S. are developing new versions of the technology. In Europe, 3D Plus has patented a stacked module technology that is also considered an embedded component package. The research was part of a four-year European program that ended in 2004 and included STMicroelectronics, CEA/LETI, Thales, Schlumberger, Cards/Axalto, Cybernetics and IBS. (1) Infineon and Imbera have also developed embedded component concepts.

Integrated passives in thin-film-on-silicon or glass substrates were introduced more than 15 years ago by AT & T Bell Labs and used in a desk phone. SyChip, a spinoff of Bell Labs researchers, developed an RF module based on the technology and was purchased by Murata of Japan. Shinko Electric developed a thin-film-on-silicon process with an embedded capacitor. STMicroelectronics and Philips each ship thin-film substrates with integrated passives.

Casio Micronics and CMK Corp. have developed an embedded wafer-level packaging (EWLP) technology. Casio has developed a prototype EWLP module that functions as a digital TV tuner. In the module, a WLP is embedded in the board with a tuner WLP and other components mounted on the board. The EWLP Consortium, formed last April to promote the technology, will work on development and standards.

Freescale developed Redistributive Chip Package (RCP) based on a batch process that features a buildup and metallization constructed on an embedded die. Freescale is targeting a number of applications with RCP, including DSPs, applications processors, base band processors, power management devices, RF transceivers, and power amplifiers.

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The benefits of embedded components are multi-die capability and, in some cases, two-sided construction in which components can be mounted on top of each other. This permits fan-out routing--important as companies look for WLP solutions or higher pin count die. It is also possible to integrate passives in some of the embedded processes, and internal EMI shielding is possible for some designs.

The technology is not without challenges. Although it has been around for decades, it has not been commercialized for IC packages. With some technologies, there have been materials and process issues. Any packaging technology that departs from the traditional infrastructure requires a new infrastructure of material, equipment and service providers. With traditional packages using known good substrates, assembly yields are typically greater than 99%. For the embedded chip in substrate, the advantage of good die will be lost to substrate buildup process yield. Thin-film versions of this technology require serial processing, creating compound yield issues.

PCBs with embedded components. The desire to increase reliability, improve performance and reduce cost has driven a significant amount of effort during the past 20 years to embed resistors and capacitors in PCBs. As with many new technologies, an undeveloped infrastructure, including supply base for materials, experienced fabricators, design tools and test methods, lack of standards, and limited reliability data has slowed widespread adoption. Early adopters implemented the technology to solve major problems.

Historically, resistors buried in PCBs were used in military and aerospace applications where solder joint elimination and weight reduction were the primary issues. Planar capacitance solutions have been designed in high-end applications to deliver moderate performance improvements. Recently, new solutions and enabling technologies have been extending the use of embedded components to mobile phones, digital cameras and camcorders, and medical applications.

In February 1999, NIST launched its Advanced Embedded Passives Technology (AEPT) project. Motorola introduced a PCB with embedded passive components in its mobile phones in late 1999. The V66 GSM mobile phone reduced the number of SMD components from 89 (51 capacitors, 16 resistors and 22 inductors) to 33 embedded components (18 capacitors, 11 resistors and 4 inductors). It also reduced the board size from 40 x 23 mm to 23 x 23 mm. (2) The AEPT program continues to produce improved technologies. Standards development began in 2003, with the IPC and Japanese Electronics and Information Technology Industries Association (JEITA) focusing on materials, design, dimensions and other specifications for embedded components. Companies that have recently developed laminate boards with embedded components include AT & S, Clover Electronics, CMK (now partnering with Casio Computer), Compeq, DT Circuit Technology, Fujitsu Interconnect Technologies, Ibiden, Matsushita Electric Industrial and Wus. (3) While Motorola is not using the substrate with integrated passives today, it shipped tens of millions of units in its products. Clover says it has supplied more than one million components with an embedded RF device since 2003.

The success of embedded active components in IC packages will depend on investment in tools in the packaging area. Materials used in fabricating the structures are also important. The industry is poised to make significant increases in the use of integrated passives in a broad range of products and applications. Just as microvia technology revolutionized the PCB industry, embedded technology has the potential to do same.

Au.: The author gratefully acknowledges contributions from Karen and Richard Carpenter in research for this article.

References

1. C. Val, "Ultra Low Profile 3-D Cube with Wafer Level Packaging Technique," International Wafer-Level Packaging Conference, Nov. 3-4, 2005, pp. 134-137.

2. "Motorola Ships Passive-Embedded PCB for Mobile Phones," Nikkei Electronics Asia, Tokyo, Japan: Nikkei Business Publications , May 2003, pp. 30-39.

3. E. J. Vardaman, "Are Embedded Passives Ready for Prime Time?" CIRCITS ASSEMBLY, July 2003, pp. 12-13.

E. Jan Vardaman is president of TechSearch International (techsearchinc.com); [e-mail]. Her column appears bimonthly.

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