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 also has 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.
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 also has been significant expansion in capacity for newer FPBGA, CSP, SIP, WLP and flip chip-based packaging (Table 1
). Projections for expansion indicate newer technologies will continue to grow at a high rate, while investments in standard leadframe technology will decline.
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 enter 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 2
) 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.
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 µm. If this type of 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 µm 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 µm in some configurations. At this thickness, many die structures are dominated by the properties of the die metal and dielectric.
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-µm 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 substrates 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.
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 also has been proposed to develop test standards based on identified failure mechanisms. (For more information, contact Bob Pfahl at iNEMI; firstname.lastname@example.org.)
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 3
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.
Roadmap 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; email@example.com.
is vice president of operations for Wispry (wispry.com); firstname.lastname@example.org. He chaired the packaging technical working group of the 2007 iNEMI Roadmap.