R&D needs for packaging: WLPs may be the answer to the widening gap between device cost and packaging cost.

The packaging industry enjoyed significant growth between 2004 and 2006, based on increased demand for semiconductor and electronic products overall. However, capacity expansion to address this growth has been conservative, resulting in some constraints in supply and higher prices. As a result, many integrated device manufacturers (IDMs) have expanded internal operations during this cycle (in parallel with increasing outsourcing) to balance the cost and risk of capital investments.

There has also been rapid emergence of new package technologies driving the need for increased R&D. Furthermore, higher complexity SIP, stack package, wafer-level packages and Pb-free packages require greater R&D coordination between the semiconductor and system-level packaging industries. The 2007 iNEMI Roadmap highlights several critical semiconductor packaging R&D areas that--if not effectively addressed--will limit future success. This article highlights some market forces driving semiconductor packaging research worldwide, and summarizes the critical research areas.

Market Trends

Over the past two years, worldwide semiconductor packaging unit volumes have been growing at a high rate, driven by a strong overall semiconductor growth cycle. Many older leadframe-based factories have returned to high utilization rates. There has also been significant expansion in capacity for newer FPBGA, CSP, SIP, WLP and flip chip-based packaging (FIGURE 1). Projections for expansion indicate newer technologies will continue to grow at a high rate, while investments in standard leadframe technology will decline.

[FIGURE 1 OMITTED]

The primary factors for higher growth rates in newer packaging technologies are the reduced size, improved performance and lower cost of these technologies. The higher growth rates have, in turn, shifted R&D focus to BGA, CSP, WLP and SIP technologies.

In parallel with the shift, the packaging industry is consolidating through acquisition of IDM facilities by subcontractors as IDMs exit non-differentiated packaging; assembly subcontractor mergers; and EMS companies' entry into packaging services to expand their product and service base. In addition, many companies are using technology development partnerships and manufacturing joint ventures to leverage R&D resources by sharing costs and reducing capital investment risk. While this type of research was historically conducted through open consortia, it has become more common to form private alliances among companies that tightly protect intellectual property and provide competitive advantage. As the industry matures, many of these consolidation activities are expected to continue.

Critical Research Needs

There are several areas where additional R&D is needed. Substrate technology, for example, continues to be a key target area with specific requirements, including improved interconnect density, reliability and reduced cost. New materials are also required to address reliability, performance and cost challenges. Thin wafer packaging and related stacked die have become high priorities since the 2004 Roadmap.

Assembly equipment, in general, is not keeping pace with needed productivity improvements, and new processing approaches are needed to shift the cost structure. There is also a need to improve design simulation and perform chip and package co-design for very high-performance systems. Integrated standards for reliability testing and product qualification are required to help bridge gaps between semiconductor and system standards.

To focus the industry on research that will yield the highest payback, the iNEMI Roadmap team identified the critical areas across the industry. Many of these research needs (TABLE 1) cut across multiple package technologies, so they address a large portion of the market. A few key examples are discussed below.

Low K copper interconnect. To improve device performance, the industry has transitioned to copper interconnect with low K dielectrics. The low K/Cu transition has created the need for research into new copper wirebonding processes, and wafer probe techniques that enable direct contact to copper metal structures. Low K materials also have created a problem with packaging because of the lower strength of these materials. Lower force bonding and development of low-stress die-to-package interconnect are needed to reduce the risk of die damage during assembly and temperature cycling. There is also a need for additional reliability research to further understand the interactions between new die structures and lead-free solder interconnections, and to develop package designs that will help reduce this risk.

Wafer-level packages. WLPs, which provide complete protection and an interconnect structure for direct mount of the die to a system board, are being developed to reduce size and cost. For this technology to reach its full potential, manufacturers must develop high-reliability WLP-to-substrate connections that can support area array pitches below 100 [micro]m. If this type package is to be broadly adopted, it will be necessary to reduce cost by eliminating expensive underfill processes.

Thin packaging and die stacking. These technologies have been developed to increase density, particularly in memory applications. However, both types require wafer thinning advancements. Today, the thinning of 300-mm wafers below 100 [micro]m leads to significantly increased breakage during handling. The reliability of these thin die, which use lower strength low K dielectric materials, is also a concern. Industry trends will drive the need to thin below 50 [micro]m in some configurations. At this thickness, many die structures are dominated by the properties

of the die metal and dielectric.

Interconnect density. As semiconductor device features continue to shrink, the gap between die-level interconnect density and package interconnect density will continue to increase. Today, semiconductor interconnection features are in production at 65 nm, while area array off-chip interconnect is limited to 200-[micro]m pitch I/O features, which are difficult to route with state of-the-art substrate technologies. The need for a radical improvement in chip-to-package I/O density and substrate density is clear, and the solutions will most likely be based on completely new approaches, rather than the evolution of existing technologies. Related to this need are requirements for new materials, including organics that can provide improved TCE match to silicon, lower moisture absorption, higher temperature compatibility and reduced cost.

Reduced packaging costs. In many market applications, semiconductor device cost has continued to drop at a faster rate than packaging cost. The 2007 iNEMI Roadmap projects a 5% per year drop in the cost per I/O for packaging, while many market sectors are driving the need for a 15% per year reduction in product cost. New technology approaches are the key to reducing package cost, particularly given recent increases in base material cost. WLP, which can eliminate many package assembly process steps, may be one technology that can help drive this cost reduction.

Reliability. Development of new test methods and reliability test standards is a pervasive theme through almost all new areas of package development. New materials and structures are much more complex and push reliability boundaries of many applications. To address this, iNEMI has proposed an industry-wide program of collaborative research to develop test methods that will help identify and characterize failure mechanisms. The second phase of this program has also been proposed to develop test standards based on identified failure mechanisms. (For more information, contact Bob Pfahl at iNEMI; [e-mail].)

SiP and 3-D packaging. Two areas of research that have evolved quickly during the last two years are SiP and 3-D packaging. SiP technology is primarily being driven by the mobile phone industry, which requires the integration of many device types into small form factor packages. SIP technology trends are summarized in TABLE 2.

3-D packaging is a longer term development focus that has the potential to shift the entire industry structure and technology base. There are many different competing approaches to 3-D, but they have some common elements, especially in terms of development needs. One critical element is the formation of high-aspect-ratio via structures that can enable interconnect of nanometer scale structures in three dimensions. Approaches to cool these extremely dense structures need to be developed.

Development Process

The packaging roadmap was developed by a group of industry experts representing IDMs, assembly contractors, equipment suppliers, materials suppliers and research groups across the industry. This group also supports development of the ITRS Packaging Roadmap. As a result, the tables on critical research needs and packaging technology are used in both roadmaps. The iNEMI Roadmap, however, provides additional information on market trends and the business conditions that impact the pace and scope of worldwide packaging research and development.

Work will soon begin on the 2009 Roadmap. Anyone interested in participating can contact Chuck Richardson, iNEMI director of roadmapping; [e-mail].

JOE ADAM is vice president of operations for Wispry (wispry.com). He chaired the packaging technical working group of the 2007 iNEMI Roadmap.

TABLE 1. Assembly and packaging--difficult near-term challenges.

DIFFICULT CHALLENGES 32 nm   SUMMARY OF ISSUES

Impact of BEOL, including    * Direct wirebond and bump to Cu or
Cu/low k on packaging          improved barrier systems bondable pads
                             * Bump and underfill technology to assure
                               low K dielectric integrity including
                               lead-free solder bump system
                             * Improved fracture toughness of
                               dielectrics
                             * Interfacial adhesion
                             * Reliability of first-level interconnect
                               with low K
                             * Mechanisms need to be developed to
                               measure critical properties
                             * Probing over copper/low K

Wafer-level CSP              * Reductions in I/O pitch for small die
                               with high pin count
                             * Solder joint reliability and cleaning
                               processes for low stand-off
                             * Wafer thinning and handling technologies
                             * Compact ESD structures
                             * TCE mismatch compensation for large die

Coordinated design tools     * Mixed signal co-design and simulation
and simulators to address      environment
chip, package, and           * Rapid turnaround modeling and simulation
substrate co-design          * Integrated analysis tools for transient
                               thermal analysis and integrated thermal
                               mechanical analysis
                             * Electrical (power disturbs, EMI, signal
                               and power integrity associated with
                               higher frequency/current and lower
                               voltage switching)
                             * System level co-design is needed now
                             * EDA for "native" area array is required
                               to meet the Roadmap projections
                             * Models for reliability prediction

Embedded components          * Low-cost embedded passives: R, L, C
                             * Embedded active devices
                             * Quality levels required not attainable
                               on chip

Thinned die packaging        * Wafer-level embedded components
                             * Wafer/die handling for thin die
                             * Different carrier materials (organics,
                               silicon, ceramics, glass, laminate core)
                               impact
                             * Establish infrastructure for new value
                               chain
                             * Establish new process flows
                             * Reliability
                             * Testability
                             * Different active devices
                             * Electrical and optical interface
                               integratio

Close gap between chip       * Increased wireability at low cost
and substrate--improved      * Improved impedance control and lower
organic substrates             dielectric loss to support higher
                               frequency applications
                             * Improved planarity and low warpage at
                               higher process temperatures
                             * Low moisture absorption
                             * Increased via density in substrate core
                             * Alternative plating finish to improve
                               reliability
                             * Solutions for operation temp up to C5
                               interconnect density scaled to silicon
                               (silicon I/O density increasing faster
                               than the package substrate technology)
                             * Production techniques will require
                               silicon-like production and process
                               technologies after 2005
                             * Tg compatible with Pb-free solder
                               processing (including rework
                               @260[degrees]C)

TABLE 2. SiP technology trends.

                                 Near-Term

Year of Production               2005   2006   2007    2008      2009

DRAM 1/2 Pitch (nm)               80     70     65      57        50
  (contacted)                     85     76     67      60        54

Number of terminals-low cost     600    600    700      800       800
  han-held
Number of terminals-high                2900   3050    3190      3350
  performance (digital)
Number of terminals--            200    200    200      200       200
  maximun RF
Low cost handheld / #die /        6      6      7        8         9
  stack
High performance / die / stack    2      2      3*      3*        3*
Low cost handheld / #die / SiP    6      8      8        8         9
High performance / die / SiP      4      5      6*      6*        6*
Minimum component size           1005   1005   1005   600x300   600x300
  (microns)
Maximum reflow temperature       260    260    260      260       260
  ([degrees]C)

                                 Near-Term

Year of Production                2010      2011      2012      2013

DRAM 1/2 Pitch (nm)                45        40        35        32
  (contacted)                      48        42        38        34

Number of terminals-low cost       800       800       800       800
  han-held
Number of terminals-high          3509      3684      3860      4053
  performance (digital)
Number of terminals--              200       200       200       200
  maximun RF
Low cost handheld / #die /         10*       11*       12#       13#
  stack
High performance / die / stack     4#        4#        4#        5#
Low cost handheld / #die / SiP     11*       12*       13#       14#
High performance / die / SiP       7#        7#        7#        8#
Minimum component size           400x200   400x200   400x200   200x100
  (microns)
Maximum reflow temperature         260       260       260       260
  ([degrees]C)

                                 Long-Term

Year of Production                2014      2015      2016

DRAM 1/2 Pitch (nm)                28        25        22
  (contacted)                      30        27        24

Number of terminals-low cost       800       800       800
  han-held
Number of terminals-high          4246      4458      4670
  performance (digital)
Number of terminals--              200       200       200
  maximun RF
Low cost handheld / #die /         14A       14A       15A
  stack
High performance / die / stack     5#        5#        6A
Low cost handheld / #die / SiP     14A       14A       15A
High performance / die / SiP       8#        8#        9A
Minimum component size           200x100   200x100   200x100
  (microns)
Maximum reflow temperature         260       260       260
  ([degrees]C)

                                 Long-Term

Year of Production                2017      2018      2019      2020

DRAM 1/2 Pitch (nm)                20        18        16        14
  (contacted)                      21        19        17        15

Number of terminals-low cost       800       800       800       800
  han-held
Number of terminals-high          4904      5138      5394      5651
  performance (digital)
Number of terminals--              200       200       200       200
  maximun RF
Low cost handheld / #die /         15A       16A       16A       17A
  stack
High performance / die / stack     6A        6A        7A        7A
Low cost handheld / #die / SiP     15A       16A       16A       17A
High performance / die / SiP       9A        9A        10A       10A
Minimum component size           200x100   200x100   200x100   200x100
  (microns)
Maximum reflow temperature         267       260       260       260
  ([degrees]C)

* Manufacturable solutions are known

# Interim solutions are known

A Manufacturable solutions are NOT known