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Fully Buffered DIMM

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Fully Buffered DIMM

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  1. Very Low ProfileFully Buffered DIMMBill GervasiVice President, DRAM TechnologySimpleTechThe subject matter of this presentation is a work in progress.  It had not been balloted or approved as a final JEDEC standard.  Users should not rely on this presentation as indicative of the content of the final standard. JEDEC does not endorse the content of this presentation.  The views expressed are solely those of the author(s).

  2. Fully Buffered DIMM • Designed for needs of mid-range servers • Typically 8 or 16 FB-DIMM slots • 4GB per slot by the time it is ramping(1Gb DRAMs)  32GB & 64GB servers • Only “standard” height is 30mm (1.2”) • Need to penetrate broader markets to ensure success and reduce cost

  3. 1.2” (30mm) standard chosen in 1999 based on 1U server market projections • But, market fragmenting • Blade needs 18.3mm (VLP) • 1U needs 30mm (LP) • 2U can use 38mm or taller • OEMs “demand” one size fits all … but … Form Factor Wars • 1.2” (30mm) standard chosen in 1999 based on 1U server market projections

  4. 38mm High Profile Module Side View 2U Server • Lots of headroom due to huge heat sinks • Tall module (e.g., 38mm) fits fine • Better thermal characteristics • More DRAM supplier options CPUHeatSink 30mm

  5. Cool Air Heated Air Standard Profile Module Blade Server Top View CPU CPU 17700 mm2 Angled Socket 30 mm DIMM

  6. Very Low Profile Module Blade Server Top View CPU Cool Air Heated Air CPU 2 x 2200 mm2 75% Reduction! Angled Socket 30 mm DIMM Vertical Socket 18.3 mm DIMM

  7. The VLP Form Factor 133.35 mm (5.25”) 18.3 mm(0.72”) 14.3 mm(0.56”)Usable Layout Area 4 mm(0.158”)

  8. FB-DIMM Differentiation • How to build a better FB-DIMM • Improved thermal solutions • How about a VLP FB-DIMM? • Challenge #1: AMB is 19.2mm tall! • Good thing guyslike us like to pack10 pounds into a 5pound sack… 19.2 mm(0.76”) 24 mm(0.95”)

  9. FB-DIMM Differentiation • Notice that the AMB has huge windows in the array • This choice was based on some assumptions: • FB-DIMM must be possible in6 layers • No blind vias required • However, what if you’re willing to go to 8 layers and use blind vias?

  10. Honey, I Shrunk the AMB 655 ball AMB29x23 ball array (ball pitch 0.8mm)24.5 x 19.5mm package 510 ball VLP-AMB31x17 ball array (ball pitch 0.8mm)26 x 14mm package

  11. Can the AMB Be THAT Small? The AMB die size is not the limiter… it’s the number of balls on the package that defines its footprint.

  12. VLP FB-DIMM Stacked 2GB

  13. DRAM Size • Max DRAM package supported in VLP = 12.3 x 14.3 mm • This supports most 512Mb chips now • 1Gb shrinks with 70 nm process • 4GB VLP FB-DIMM enabled

  14. A Simpler Variation • Primary-only interface – no southbound • Uses 4-channel memory controller • Eliminates 100 balls, 1W per AMB “Low End” FB-DIMM Controller “High End” FB-DIMM Controller

  15. Current Status • Getting customer input on primary-only AMB • Mechanical feasibility done • Re-ballout analysis under way with AMB suppliers • Thermal analysis under way • Improved airflow with lower ambient • Less radiating space • Heat sinking solutions to be developed • Socket analysis begun

  16. Thank You • Questions? Bill Gervasibilge@simpletech.com

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