1. 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

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

3. 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

4. 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.

5. 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

6. 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

7. 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

8. 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

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

10. 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

11. 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

12. Surface issues
Uncontrolled flow pattern
Underfill delamination

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

14. Yield improvement (Underfill related failures)

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

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

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

18. 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.

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

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

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

22. 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

23. 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

24. 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

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

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

27. 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

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

29. Transition to Optical links borrowed from M. Duranton \ HIPEAC