Shuki Benjamin et al Compass-EOS & PVA TePla AG 336-Channel Electro-Optical Interconnect: Underfill Process Improvement, Fiber Bundle and Reliability Results Shuki Benjamin et al Compass-EOS & PVA TePla AG

Agenda / Outline / Overview Introduction Underfill Fiber Bundle Assembly Reliability Results Summary

Evolution of Fiber Connectivity When wires ran out of capacity… Between Chips Between Data Centers Between Cities … the world moved to fibers Between Countries Between Continents 1980’s 1990’s 2000’s 2010’s

Motivation for Optical Interconnect With higher bandwidth on Cu lines Transmission lines (density!) Equalization (Energy!) Larger systems and large buildings -> more to cool Fans ! Air condition ! In 2012: The relative share of ICT products and services in the total worldwide electricity consumption was more than 4.6%(*) * W. V. Heddeghem et al., Computer Communication, In Press.

icPhotonics™ - Fastest Optical Interconnect Multi Terabits Full Duplex Bandwidth 1.34 Tb/s in production networks today Over 10Tb/s with next gen chip Highest Chip I/O Density 64Gb/s per mm2 20X higher than other solutions Passive optical links that stretch to Hundreds of Meters vs. Centimeters with Electronics Laser Matrix Photo Detectors Standard I/O

Scaling icPhotonics™ to 10 Tb and Beyond Scale-Up Increase Optical Speed 8 Gb/s Per Channel 32 Gb/s 4X 8X Next Gen: 10.7Tb/s SHIPPING Scale-Out Enlarge Optical Matrix 12 x 14 12 x 28 2X Today: 1.34Tb/s

Optical Interconnect features Direct Coupling to ASIC Chip Low energy consumption: 10pJ/bit (including SERDES) Patents Covering Technology & Processes Flexible form factor Ready for Mass Production

Challenges that had to be solved Standard wafer processes Flip-chip and reflow – standard equipment The optics created new challenges: Underfill Large format fiber-bundles Reliability

Agenda / Outline / Overview Introduction Underfill Fiber Bundle Assembly Reliability Results Summary

Underfill Challenges Some of the usual: But two new… Big die (>400 mm2), Large bump count (~7000) Different bump pitch across the die But two new… A hole in the middle of the die with tight tolerance on overflowing the optical dies Requires a strict control of surface state before applying underfill 20.1mm 20.5mm

Underfill Flow pattern – a complete rectangle around the chip (!) No void concern – air is escaping from the middle Solving the “overflow” issue – options*: Mechanical stop UV cure through the hole Quantity control Controlling the surface A better flow pattern control Enhance adhesion * Acknowledging the work by Karl Becker and his group at Fraunhofer-IZM

Surface issues Uncontrolled flow pattern Underfill delamination

Plasma treatment RF plasma MW plasma Physical ion bombardment Perpendicular impact (shadow) MW plasma Chemical reaction using free radicals More isotropic effects

Yield improvement (Underfill related failures)

Underfil summary Using MW plasma enabled to control the surface chemistry Un-orthodox underfill process presented

Agenda / Outline / Overview Introduction Underfill Fiber Bundle Assembly Reliability Results Summary

High-Density Fiber-Bundle The icPhotonics™ is always conjugated to a Fiber-Bundle The challenges: Easy to align (tolerances) Reliability Manufacturability Cost

Fiber-Bundle: Allignment and Reliability Two-lens system allows for loose tolerances and easy assembly Proprietary glue mixture and gluing process enables reliable connection Standard MT ferrule connector for easy connection to the back-plane.

Fiber-Bundle Assembly Si Template (cost, process control) Fiber-ribbons (manufacturability) Fiber insertion (gigs, ready for automation) Cover and glue

Fiber-Bundle - Summary In Production Acceptable price Qualified Reliable Two 12X14 fibers in bundle connecting modules through optical backplane

Agenda / Outline / Overview Introduction Underfill Fiber Bundle Assembly Reliability Results Summary

Reliability NEBS qualification \ Telcordia GR-63-CORE Optical dies Optical dies to ASIC Bundle assembly to PCB ASIC PCB Substrate Tx Rx (iii) Bundle assembly reliability Bundle (ii) Optical die to ASIC (i) Optical dies reliability

Optical Dies Reliability Commercial qualified components Accelerated aging Custom Si dies – each pixel operated and controlled, each die monitored Tested for optical power (VCSEL’s) and dark-current (PD). Infant mortality < 1% => no burn-in required (a) (b) (c) Fail criteria

Optical dies to ASIC - Reliability Custom Si and III-V DC dies Standard assembly – 25 units ( => 16,800 connections) TC (-400C / +800C, 1000 cycles)* Accelerated aging (1700C, 1300hrs – equivalent to 10 years normal operation)* NO FAILURES ! * Acknowledging the work by Hermann Oppermann and his group at Fraunhofer-IZM

Bundle assembly Reliability Temperature & Humidity: 250C – 550C 95% Temperature cycles: -200C – 600C (n=1000) – no failures Vibrations ±1 dB ±1 dB

Agenda / Outline / Overview Introduction Underfill Fiber Bundle Assembly Reliability Results Summary

Summary Several new aspects of icPhotonics™ based Optical Interconnect were demonstrated Using MW plasma to control surface chemistry enabling an un- orthodox underfill process Large-Format Fiber-Bundle assembly Reliability results presented icPhotonics™ Technology allows system designers to triple high-speed SERDES count into and out of the ASIC die, enabling more efficient systems, reducing energy demands and latency

Next step for more high BW interconnection High density, High speed Courtesy of J. Matsui, FUJITSU Laboratories LTD. Copyright 2014 FUJITSU Laboratories LTD.

Transition to Optical links borrowed from M. Duranton \ HIPEAC