Convergence of 3D integrated packaging and 3D TSV ICs
As fan-out technology production ramps and exposure to the technology grows in the industry, there is an interesting set of opportunities emerging. Although RCP technology can provide distinct advantages over both wirebond and flip chip single die packaging solutions, a closer evaluation of fan-out suggests that a more pronounced advantage is possible in the form of a multi-die, or system-in-package (SiP) solution. The RCP multi-die program is specifically designed to incorporate several of these advantages: heterogeneneous integration (die, passives, peripherals), system miniaturization, system performance, system cost, high speed in package computing, system flexibility (chip sourcing, integration), block testability, and a path to integrating with 3D TSV ICs.
Navjot Chhabra, Freescale Semiconductor, Austin, Texas, USA
Beginning in the 1990s and coming into its own in early 2000s, three dimensional (3D) through silicon via TSV IC technology has demanded a significant amount of attention. It became apparent as process and design rules continued to migrate down Moore's law that the challenges of having robust materials and chip performance were becoming a significant concern. Some of the motivations driving the development of 3D IC and TSV technologies are the increasing on-chip, high-speed signal paths as well as utilizing optimum functional blocks within the chip design. While die-to-die interconnects address many of the device functionality challenges, a number of processibility and reliability concerns remain. The hurdles to 3D integration begin with the design and modeling infrastructure and continue with clear needs for process and materials development, decreasing costs through improved yields and, ultimately, alleviating ongoing reliability concerns.
There is another technology path emerging in the industry. Similar to the evolution of front-end wafer processing, package technologies are also evolving. Historically, the motivation behind the typical packaging roadmap has been driven by the need to meet decreasing package sizes (x,y,z), lower costs, increase performance, and provide different reliability requirements and thermal and electrical compliance. However, within each packaging category the challenges of meeting certain reliability grades and functionality still remain. Similar to the ‘red brick wall' seen on the ultra-low-k material roadmap, wire bond technology is beginning to see that similar concern. As die technology keeps advancing and more functionality is required, the ability to route signals without impacting performance and cost is a great concern. While the overall die cost continues to decrease with advancing nodes, package costs are heading in the opposite direction.
In the 1980s, companies began the development of fan-out packaging technology. The idea was to eliminate the need for substrates and gold wirebond, two of the highest cost items in a package bill of materials while, at the same time, addressing some of the limitations of contemporary packaging. In 2007, Freescale introduced a fan-out technology called the redistributed chip package (RCP) built on a 300mm tool set. This specific technology is targeted at meeting the requirements listed below.
Package size reduction: ~30% size and thickness reduction vs. PBGA; package size and routability: one to six signal redistribution metal layers (RDL) and a package size ranging from 2x2mm, to as large at 40x40mm; yields: assembly yield comparable to today's packages; a cost-competitive, high productivity, large area batch process that eliminates the package substrate and eliminates gold wire bonds/C4 bumps; high-performance package with electroplated copper interconnects, reduced electrical parasitics, improved device efficiencies, higher frequency response, and active structures in routing (shielding, inductors); ultralow-k compatible (<90nm MLM) and compliant with advanced silicon technology. Additional requirements are: lead-free, halogen-free, and ROHS compliant; single chip, multiple chip and embedded component capability; 3D IC enabling with system integration roadmap; certified to JEDEC/commercial/industrial level reliability; and meets or exceeds JEDEC requirements for solder joint reliability and drop test.
In early 2009, RCP achieved both commercial and industrial-level certification on multi redistribution layer parts with a range of package sizes. This technology is also well underway towards meeting automotive level requirements. With thousands of 300mm panels produced to date, yields continue to achieve benchmark levels.
Meeting the analog challenge
The use of RCP technology for digital applications was fairly straight forward, however, its adoption for analog applications had additional challenges. Not only were the end user requirements much more stringent, well beyond JEDEC commercial specifications but the electrical parameter tolerances were dramatically tighter. Process and design enhancements to the RCP technology provided the solution with the added benefit of enabling ~20% reduction in die size, which had a significant benefit to both chip performance and cost.
Freescale RCP multi-die systems currently being developed and sampled to end users are incorporating embedded surface mounted devices, discrete components, active RF features, shielding and thermal management structures while providing better system performance and shorter design cycles. For even more integration and performance, these two dimensional multi-die packages are being built in multiple, 3D planes and 3D integrated packages (Fig. 3).
|Figure 1. Convergence of 3D IC with 3D integrated packages.|
As highlighted by the roadmap (Fig. 1), having the flexibility to design complex systems in a true system is a significant product and application enabler. Being able to integrate with the results of parallel development in 3D ICs provides the industry an appealing high performance, advanced integrated system. At this stage, the applications are extremely broad (Fig. 1).
Freescale is actively engaged in developing and providing RCP package solutions for medical applications, aerospace and optical devices, compact system solutions, advanced robotics and other technologies. Solutions involve the integration of discrete ICs ranging from two to more than 10 components along with added surface mounted devices. Packages in combination of 2D and 3D planes with thickness of < 0.5mm (3D stack) including solder spheres are being sampled. As the need to integrate MEMS devices and advanced memory for sensor applications expands, work is underway to develop modules merging both mechanical and electrical devices into single, highly compact modules.
Navjot Chhabra received his BS degree from Boise State U. and is the RCP development and operations manager at Freescale Semiconductor, 6501 William Cannon Drive West, MD OE:08, Austin, Texas 78735, USA; ph.: (512) 895-6470; email Navjot.firstname.lastname@example.org.