Are embedded passives ready for prime time? Key players and innovations shape the future of embedded components.

Along with the demand for cost savings and size reduction in electronics components has come the push for embedded passives in organic substrates. Embedded passives in ceramics have made this technology a lasting choice for many applications, but laminate technology has been elusive. Company representatives discussed the drivers for embedded passives at the 2003 InterNepcon Japan conference. Motorola described the addition of new features in existing form factors and efforts to shrink the area occupied by core phone functions.

Motorola's Demonstration Products

Low temperature cofired ceramic (LTCC) substrates with embedded passives have been in production for many years and are especially popular in Japan and Europe. However, embedded passives in organic substrates are relatively new. Motorola introduced a printed circuit board (PCB) with embedded passive components in its mobile phones in 1999, making use of microvia technology and spiral inductors. The company compared a board with embedded passives to one with conventional surface-mount device (SMD) technology and found that board size was reduced from 40 x 23 mm to 23 x 23 mm. The number of SMDs in the phone was reduced from 89 (51 capacitors, 16 resistors, 22 inductors) to 33 (18 capacitors, 11 resistors, 4 inductors) with the use of embedded passives.

In production, boards with embedded components are expected to provide lower system manufacturing cost. Motorola has also reduced cost by switching from a mobile phone design using an LTCC with embedded passives for the radio frequency (RF) module to a PCB with embedded components, reducing total manufacturing cost by one dollar. (1)

The Players

Among the Japanese companies that have developed laminate boards or IC package substrates with embedded passives are Clover Electronics, CMK, DT Circuit Technology, Fujitsu Interconnect Technologies, Ibiden, Matsushita Electric Industrial, Mitsubishi Electric and Shinko Electric. In Europe, AT&S is supplying boards with embedded components, while in Taiwan, WUS Printed Circuit Co., Ltd. has the technology to produce substrates with embedded components.

Mitsubishi Electric has introduced a technology in which the embedded inductor and capacitor are formed using the thin dielectric layer in the organic substrate. (2) Shinko Electric has developed an embedded thin chip capacitor for an organic package, which is fabricated on a thin silicon substrate and can be embedded into the build-up layer of an organic package. (3)

Global Standardization Activities

Numerous organizations are developing the infrastructure for embedded components. Organizations such as the Japan Electronics and Information Technology Industries Association (JEITA) are working on standardization for embedded components. In early 2003, an industry seminar sponsored by the U.S. Department of Commerce Advanced Technology Program (ATP) and the National Institute of Standards highlighted the final results of the Advanced Embedded Passives Technology Consortium (AEPTC). The ATP was almost exclusively devoted to process improvements for embedding passives as part of the board fabrication process. The consortium also developed standard patterns and test procedures to make the evaluations.

Process Developments

Process innovations for embedded passives can be categorized as either direct deposited, where the embedded components are deposited as part of the equipment assembly process, or off line, with components deposited as part of the PCB fabrication process.

Film devices can also be fabricated with printing and other processes. Xanodics, a new start-up from the University of Arkansas, is focused on a copper and tantalum-based process to form resistors and capacitors on liquid crystal polymer film. The structure is 75 [micro]m thick and provides 150 to 200 n F/[cm.sup.2] of decoupling with less than 3pH of parasitic inductance.

Designing the circuit so the embedded passives are a specific layer of the fabrication process optimizes the specific materials required for each component type. Since using PCB material as a substrate places an upper thermal limit on the processing that can be used to develop desirable characteristics, some off-line work allows more flexibility to get better results.

The best example, developed by DuPont and Coretec, uses copper metal as the substrate. Relatively conventional high temperature ceramic resistor and capacitor materials are deposited on the copper and fired at a high temperature in nitrogen. The resulting copper sheet with deposited components is laminated to a regular prepreg epoxy sheet. The copper is then imaged to form traces for connection to the other layers of the PCB. Materials characteristics approach those of conventional chip components.

3M's development, exclusively for dielectrics, consists of coating a suspension of high dielectric constant barium titanate onto copper. Although this coating has a low dielectric constant, very thin layers can be made so that useful capacitance can still be accomplished. Because the coating is done separately, the layer can be thin, uniform and pinhole-free.

Future Needs

Regardless of the approach, some level of trimming of resistors, and perhaps capacitors, will be required for embedded components. In chip form, ceramic chip capacitors are sorted into narrow capacitance ranges for some applications. Jetting of either resistor of capacitor material (actually counter electrode material) affords the capability to trim up as well as down. Lamination of the resulting layer into the full PCB stack can cause value shifts that either need to be compensated for or controlled.

In the future, we may be able to deposit materials with discrete ceramic component characteristics directly onto a PCB material or other low-cost, low-temperature substrates. While a lot of work remains and maturity is still required, much progress has been made.

References

(1.) M. Kawai. 2003. Motorola Ships Passive-Embedded PC8 for Mobile Phones. Nikkei Electronics Asia. Tokyo, Japan: Nikkei Business Publications . May, pp. 30-39.

(2.) U Shigeru and O. Seiji. 2003. Electrical Properties and Reliability of Organic Integral Passives Substrate. ICEP Proceedings. Tokyo, Japan, pp. 199-204.

(3.) Y. Horikawa, et al, 2003 Development of Embedded Thin Chip Capacitor into Organic Package. ICEP Proceedings. Tokyo, Japan, pp. 205-208.

The author gratefully acknowledges contributions from John Thome in the research for this article.

E. Jan Vardaman is president of TechSearch international, Austin, TX; e-mail [e-mail].