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AOC Performance. Death rates Channel distribution & FEA Decrease in optical power with time Summary. VCSEL Failures. 20 AOC channels have failed. Failure rate << TL but still much higher than expected. AOC. AOC Failures (Steve McMahon). 3 infant mortality and 17 random failures
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AOC Performance • Death rates • Channel distribution & FEA • Decrease in optical power with time • Summary
VCSEL Failures • 20 AOC channels have failed. • Failure rate << TL but still much higher than expected. AOC
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.
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.
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
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
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
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.