Issue



Infrastructure matures as Flip chip takes off


09/01/2001







E. Jan Vardaman, TechSearch International Inc., Austin, Texas

Flip chip technology has already expanded in two major areas: one driven by the high performance needs of microprocessor, ASIC, and high-end DSP devices, the other driven by form factor, where die sizes are small and packaging cost must be as minimal as the package itself. What's new is flip chip's expansion into the interconnect realm previously dominated by wire bond. This potential expansion of flip chip into mid-range pin counts signals a shift in the adoption of the technology, improvements in the industry infrastructure, and industry maturity, which will, in turn, be reflected in future cost reductions [1].

Infrastructure issues
Historically, the major barriers to the expanded use of flip chip technologies have been the lack of low-cost bumping services, low-cost substrates, and flip chip bonding and mounting equipment, as well as difficulties with underfill. Major improvements over the last four years have removed or reduced many of these barriers. Developments in the infrastructure include the introduction of new, low-cost methods for wafer bumping, an increasing number of subcontract assembly services with growing capacity, and bumping for 300mm wafers.


Figure 1. Solder-bumped FCIP and FCOB growth.
Click here to enlarge image

TechSearch International's recent analysis for wafer bump capacity shows that solder-bumping capacity is still ramping, despite a slowdown in the IC market this year. Many companies have plans in place to expand solder-bumping capacity through 2003. Even with the fast expansion of new capacity for solder bumping, demand is outstripping qualified supply. Today's merchant solder-bumping service providers include APack, Aptos, Advanced Semiconductor Engineering (ASE), Casio Micronics, Chipbond, Fujitsu Tohoku, K&S Flip Chip Division (formerly Flip Chip Technologies), MEGIC, MicroFab Technology, MicroScale, Orient Semiconductor Engineering (OSE), Shinko Electric, Siliconware Precision (SPIL), and Unitive Advanced Packaging Solutions (also known as Unitive Electronics). Solder bump capacity at Citizen Watch is included in the merchant numbers, even though the company uses much of its capacity internally. Advanpack Solutions (APS) in Singapore and Amkor Technology in Korea are expected to have qualified production available in 2002. Merchant capacity for electroless Ni/Au-bumping service providers includes such vendors as IC Interconnect and Pac Tech Packaging Technologies.

The industry has moved from a critical shortage of gold-bumping capacity a few years ago to an overcapacity this year, resulting in lower prices for bumping services. While captive manufacturers in Japan did not increase gold-bumping capacity, expansion by service providers such as Casio Micronics, coupled with the entry of many companies from Taiwan, Korea, and Singapore, expanded gold bump capacity. These entries, along with slower economic growth for 2001, have resulted in overcapacity for gold bumping. Over time, consolidation in the merchant supplier market is expected, and market overcapacity will decline as demand increases. In addition, some merchant gold bump service suppliers are likely to slow expansion plans for the remainder of this year and next. Solder bumping remains under capacity, despite the introduction of many new players and the expansion of capacity at existing suppliers. Solder bump capacity is expected to remain below demand for the next year.

In keeping with the environmentally friendly marketing movement, many merchant bumping operations have introduced or have R&D activities for lead-free bumping methods, and some products using lead-free bumps have been introduced. Discussions at a recent workshop in Austin, TX, included the presentation of lead-free bump research results by the K&S Flip Chip Division (formerly known as Flip Chip Technologies), and Ericsson (with its research work at the Georgia Institute of Technology). Universities, including Auburn University, Georgia Institute of Technology, and the National Cheng Kung University in Tainan, Taiwan, have published reliability results with lead-free solder materials.

The industry has long desired improvements in the underfill process such as more speed and shorter cure times. New "Snap Cure" materials have been introduced, reducing the required cure time from hours to 30 min. The introduction of no-flow underfills offers promise for the future and has been addressed by a variety of companies, including Loctite/Dexter, National Starch and Chemical, Namics Corp., ThreeBond, and 3M. Reworkable underfills remain the "Holy Grail" for flip-chip-on-board (FCOB) applications.

Nearly 20 companies offer flip chip bonders and mounters, each suited for a particular application. Bump inspection systems from at least eight companies are available. Improvements in equipment for flip chip assembly have enabled the technology by allowing the user to select the equipment that provides the required trade-off in accuracy and speed.

The expansion of flip chip for many applications has been hindered by the shortage of known good die. Recent workshops have addressed the issues of bare die testing, but cost-effective burn-in at the wafer level remains elusive.

Expanding flip chip applications
Typically, flip chip has been selected for performance reasons for a number of computer and telecommunications applications. Flip chip interconnect has long been used for mainframes and supercomputers. Companies like Fujitsu, Hitachi, and IBM have used flip chip for performance reasons for many years. NEC has also recently introduced flip chip in its mainframes and supercomputers.

Driven by performance, new CPU designs for processors used in desktop and laptop computer applications feature flip chip in package (FCIP). FCIP is used in products such as AMD's processor family, Intel's CPUs, Motorola's PowerPCs, and Transmeta's processors [2, 3].

The introduction of chip sets with flip chip interconnect for PC applications is also performance driven and represents a movement into the sector previously occupied only by wire bond [4].


Motorola flip chip plastic ball grid array (PBGA).
Click here to enlarge image

Telecommunications and network system applications are also using flip chip interconnect for performance reasons. DSPs and fast SRAMs from Motorola and Texas Instruments use flip chip interconnect. Almost every ASIC supplier's high-end products are provided as FCIP for workstation/servers and network system products. Companies such as LSI Logic are offering flip chip packaging solutions to take the place of options previously dominated by wire bond. Flip chip devices are used as single-chip packages in a variety of applications, including Internet backbone switching applications. Flip chip interconnect offers electrical and thermal performance advantages for switching systems and is useful for reducing net lengths and overall board and system size. High-performance ICs used for network system providers such as routers are increasing in pin count and complexity similar to server makers having ICs with thousands of I/Os mounted in packages with more than 2000 balls or columns.

Size, weight, and form factor demands have driven flip chip into consumer applications like watches and mobile communications products such as pagers. Portable consumer products also use flip chip, mostly inside single- or multichip packages. A few applications such as Motorola's pagers, however, use flip chip directly mounted on the product board. Interesting sensor applications using flip chip for a variety of products are also emerging.

Applications like watch modules and automotive electronics are well known for FCOB packaging solutions, and represent some of the highest volumes in number of units shipped over the last 20 years. More than 200 million flip chip devices are shipped for watch modules each year. Disk drive makers such as Fujitsu, IBM, and Seagate have been using flip chip in hard disk drives for many years as flip chip on flex (FCOF). Flip chip interconnect is used for the preamplifier chip that provides the signal on the flying read-write head that moves along the disks. Figure 1 shows growth in demand for solder-bumped ICs like FCIP and FCOB, which is projected to double from a little over a billion units this year to 2 billion+ units by 2003.

The future of flip chip
The anticipated growth in the flip chip market is finally becoming a reality as a result of performance and form factor drivers coupled with infrastructure developments. The major remaining challenge is the widespread commercialization of cost-effective testing at the wafer level. While some excellent work has taken place, advances are still needed. Despite the slow growth in the electronics sector for 2001, the future for flip chip is bright. Many development programs, while experiencing slight delays, remain focused on future volume applications. An increasing number of devices of all types will be bumped.

References

  1. E.J. Vardaman, L. Matthew, "Flip Chip Market Trends," IMAPS Baltimore, Oct. 2001.
  2. R. Shukla, V. Murali, A Bhansali, "Flip Chip CPU Package Technology at Intel: A Technology and Manufacturing Overview," 1999 Electronic Components and Technology Conference Proceedings, pp. 945-949, June 1-4, 1999.
  3. R.N. Master, "Flip Chip Packaging for PC Microprocessors," APEX Proceedings, p. AT6-2, Jan. 14-18, 2001.
  4. E.J. Vardaman, "Flip Chip Infrastructure and Market Developments," IMAPS Nordic, Sept. 2001.

E. Jan Vardaman is the president and founder of TechSearch International Inc., a consulting company that provides technology licensing, strategic planning, and market and technology analysis for the semiconductor packaging industry. For more information on the flip chip market, see the company's study Flip Chip Markets and Infrastructure Developments. TechSearch International Inc., 4801 Spicewood Springs Rd. Ste. 150, Austin, TX 78759; ph 512/372-8887, fax 512/372-8889, e-mail [email protected], www.techsearchinc.com.