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.

3000 5000010000

0.050.1

0.51

510

50

99

0.01

CERN Field Failure Data (Lognormal Probability Plot)

Time in service (hours)

Cum

ulat

ive

Per

cent

age

Fai

led

(%)

Orig

inal

unp

rote

cted

par

ts (6

00 fa

ilure

s)

Current dielectric-encapsulated parts (20 failures)

1 ye

ar

2 ye

ars

Anticipated failure rate for

dielectric-encapsulated VCSELs

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.

1 2 3 4 5 6 7 80

1

2

3

4

5

6

7

8

Random

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.

PCB 1.6 mm

Silver Epoxy <10 umGaAs 120 um

Epoxy 50 um

Material CTE (ppm/ °C) Y (Gpa) Density g/cm3

FR4 PCB 175 (z) or 13 (x) 0.5 1.9

Epoxy 353-NDTg ≥ 90oC

54 (below Tg)/ 206 (above Tg)

3.56** 1.06

GaAs 6.86 85.5 5.3

H20E 31 25 (guess) 2.55

Cure temperature: 100°C, normal operating temperature 20°C

5Diagram and parameters provided by Tony Weidberg

**http://www.epotek.com/SSCDocs/datasheets/353ND.PDF

08 Oct 2012

6

GaAs stress: Max stress along its length on GaAs is 140MPa ;

GaAs displacements: Max out-of-plane displacement is 0.022mm; and max in-plane displacement is 0.072mm.

Max von-mises stress of GaAs is 173MPa

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

Group results by 4 installation periods

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.

Radiation Damage p-i-n diode? No