Jerome Baron -- Yole Développment
Baron reviewed the status of interposer applications, markets, players and costs. Several of the following speakers would tout the potential of glass as an interposer substrate material due to its perceived lower cost position, outstanding Rf performance, and its ability to be fabricated in large format. Baron compared and contrasted glass and silicon based interposers in the chart below. Henry Utsunomiya, president of Interconnect Technologies Inc., later predicted that glass interposers would be used for FC -- CPU and GPU starting in 2013.
Glass producers in the audience such as Corning Glass and Asahi Glass indicated that they were actively pursuing glass interposer technology as part of the GaTech consortium program. Christian Nopper, R&D director of ST Micro-Tours, indicated that glass substrates are already being used for their Rf IPADS technology [Integrated Passive and Active Devices].
Yole concluded that panel size processing will be mandatory for 2.5D interposers to be broadly adopted in the packaging landscape.
Rao Tummala -- GaTech
Rao Tummala, founding director of the GIT Packaging Research Center, laid out the case for the GIT Interposer consortium. They are studying both silicon and glass interposers and view their low-cost large-panel size solutions as eventual replacements for the BGA packages currently supporting the interposer and chips. Their low-cost silicon solution is linked to the use of polysilicon vs. crystalline Si wafers.
In his presentation on the electrical issues of interposers, GIT's Madhaven Swaminathan pointed out that glass has lower insertion loss and a higher level of insulation than CMOS grade silicon, but glass has return path discontinuities so the insertion loss can be much higher than silicon. Looking at eye diagrams for glass and silicon, they actually concluded that silicon is the best.
- Insertion loss is higher, but there are workarounds;
- Crosstalk can be a killer;
- Better thermal performance spreads the heat and reduces cross talk;
- Better power delivery
- Insertion loss is low;
- Crosstalk is low;
- Localized heating is a problem;
- Power delivery could be challenging
Nanhoom Kim of Xilinx pointed out that there are several physical limitations imposed on the interposer due to cost, manufacturability, and reliability.
Kim also showed that when it comes to electrical performance, thicker oxide, shorter TSV, and smaller diameter are better.
Choon Lee, head of corporate technology for Amkor, reminded us that all DRAM is not equal. 4Gb DRAM DIMM for servers costs ~$250 whereas 4Gb DRAM for a PC is ~$20 -- quite a difference. It's clear why stacked memory is first headed for server applications!
Kai Zoschchke from Fraunhofer IZM provided this convenient plot of TSV resistance vs. aspect ratio:
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Next week: Update on 3D activities at the 2011 IEEE IEDM.