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AOC Performance

This report examines the performance and failure rates of Active Optical Cable (AOC) VCSELs, revealing a significantly higher death rate than anticipated. Notably, 20 AOC channels showed failures, with a peak in central channels indicating potential packaging issues. Finite Element Analysis (FEA) highlights stress discrepancies due to the mismatch in coefficients of thermal expansion between epoxy and GaAs materials. Additionally, the long-term optical power decrease observed is approximately five times greater than expected, necessitating further investigation into the causes and implications for future installations.

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AOC Performance

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  1. AOC Performance • Death rates • Channel distribution & FEA • Decrease in optical power with time • Summary

  2. VCSEL Failures • 20 AOC channels have failed. • Failure rate << TL but still much higher than expected. AOC

  3. AOC Failures(Steve McMahon) • 3 infant mortality and 17 random failures • Failures appear to peak at centre of array • Probability (More fails in one channel than observed) = 0.06% • If this is not a fluctuation  problem is not inherent to array but must be a result of the packaging.

  4. FEA Analysis(Stephanie Yang) • Epoxy on top surface VCSEL causes stress because of mismatch in CTE epoxy and GaAs and change in T between epoxy cure and operation.

  5. Cure temperature: 100°C, normal operating temperature 20°C Epoxy 50 um GaAs 120 um Silver Epoxy <10 um PCB 1.6 mm **http://www.epotek.com/SSCDocs/datasheets/353ND.PDF 08 Oct 2012 Diagram and parameters provided by Tony Weidberg

  6. GaAs stress: Max stress along its length on GaAs is 140MPa ; Max von-mises stress of GaAs is 173MPa GaAs displacements: Max out-of-plane displacement is 0.022mm; and max in-plane displacement is 0.072mm. 08 Oct 2012

  7. Power Changes(Will Kalderon) • Use on-detector p-i-n diode current Ipin to monitor power of VCSELs • Look for long term trends • Split samples into installation periods. • Check for evidence of radiation damage to p-i-n diodes

  8. Group results by 4 installation periods

  9. Summary • Death Rate for AOC VCSELs much higher than expected. • Peaking in central channels  packaging issue • FEA stress larger in centre of array • Decrease of power with time is ~ 5 times larger than expected. • Should expect the rate of decrease to get worse with time according to Bob Herrick.

  10. Radiation Damage p-i-n diode? No

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