Harness QA and Assembly to Barrels

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Status report of the ATLAS SCT optical links
John Matheson (RAL) for the ATLAS opto-links team

• links architecture
• total dose radiation hardness
• investigation of SEU
• cooling issues
• mechanical issues
• system tests
• pre-production harness
• conclusions

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silicon barrel module

• silicon microstrip detector
• readout chips
• need timing, trigger, control in
• need data out
• optical links for low mass, crosstalk

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links architecture

• 40 MHz clock and control on single fibre
• by biphase mark encoding
• 2 data fibres/module, 40 MHz NRZ

radiation hardness (10yr) 10 Mrad, 2?1014
1 MeV neutrons cm-2
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power budget
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barrel harness

• DORIC and VDC
• opto package (2 VCSELs, 1 p-i-n)
• power tapes, redundancy system
• furcation tube (now black !)
• each harness serves 6 modules

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VCSEL irradiation 1

• 20 VCSELs irradiated at INER, Taiwan
• 30 MeV protons, 2?1014 cm-2
• 168 hr at 10 mA, 168 hr at 20 mA

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VCSEL irradiation 2

• VCSELs degrade i.t.o. threshold, efficiency
• injection annealing foreseen in ATLAS
• 60 Mrad gamma - little change

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VCSEL ageing

• 20 VCSELs aged at 100C for 2534 hr
• no failures

R (1/N?t) ln(1/(1-C))
AF (I2/I1)2 expEA/KB (1/T1 - 1/T2)
duty cycle during data transfer 50 fraction of
time sending data 50 fraction of time LHC
operates 33
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Irradiation of other components

• VDC/DORIC 50 Mrad, 2.51014cm-2 n
• 1 week at 100C no failures? ? 0.3 max chip
  failure in SCT (redundancy makes OK)
• wafers being qualified for production
• p-i-n diode 11015cm-2 n, 0.5 ?0.35 A/W
• aged 60C ? ? 5 failures in SCT
• passives 31014cm-2 24 GeV p, no change
• opto-flex assembly 31014cm-2 24 GeV p,
  behaviour as expected from component-level
  irradiations

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single event upset
energy deposition in p-i-n diode may cause SEU
window A gt command bit error
window B gt BC clock error clock arrives up to
6.25ns early ABCD may lose synchronisation
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single event upset in command signals

• Links measured in loop-back mode
• measure errors in command bits

loop-back link
DORIC
VDC

• SEU irradiations at PSI
• pions, protons 300-500 MeV/c
• vary light power
• DORIC threshold varies

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single event upset in bunch crossing clock
BC clock SEU measured in 24 GeV PS beam

• forward module in beam - optical link
• barrel module in counting room - Cu link

L1 trigger beam spill L1 triggers

• BC counter of ABCD is read out after each L1
  trigger
• difference between the modules gt SEU

?SEU ? error rate (s-1) / flux
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single event upset summary

• minimum Ip-i-n 75?A
• max SCT flux 2?106cm-2s-1
• fraction of module data lost

9 ? 10-4 command bit (worst case) 7.8 ? 10-5 BC
clock error
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cooling measurement 1

• heat load from chips 0.4W
• defines T at opto-package
• component lifetime is T dependent
• need to get the heat to the cooling block

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cooling measurement 2

• dT1 through flex
• T drop dT1 dT2 dT3
• minimise dT1 using vias below chips
• AlN backing, BN-loaded epoxy

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cooling measurement 3

• total dT 18C at -7C ambient
• expect opto-package T 0C
• up to 10C tolerable for lifetime
• FEA predicts total dT 25C with no heat
  transfer to environment, shows importance of vias

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mechanical issues design clearance
clearance between top of opto-package/chip cover
and lower side of module is most critical point
compliance of flex must compensate variations in

• barrel eccentricity
• tape stack height

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mechanical issues clearance measurement
clearance measured using jig (Geneva) and
envelope module
worst case uses max. barrel eccentricity, 6 tapes
to push opto-package upwards
1.4mm clearance measured using slip gauges in
agreement with the design value
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CERN system test a surprise
send 2 closely spaced L1 triggers module being
read out when second trigger arrives
excess noise correlated with position
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CERN system test - light leaks
excess noise is due to light leaking from optical
fibres different colour furcation tubes measured
at RAL - black is opaque
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first pre-production harness

• harnesses to be made by Radiantech Inc, Taiwan
• before full-scale production, 8 pre-series
  harnesses will be made
• pre-series harnesses to be used in system test
  at RAL with at least 6 modules at low T on B3
  sector
• first harness received August 02
• some minor issues to be resolved
• optical links are fully functional

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pre-production harness bit error rate
measurements
ttc link operating point
data link operating point
both links have been operated for 12 hr with no
errors
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pre-production harness towards a system test at
RAL

• barrel module on pre-series harness
• fully functional, 1600 e- noise
• pre-series tests completion will define start of
  production in industry

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conclusions

• SCT harnesses must be rad-hard to 10Mrad, 1?1014
  n/cm2
• fibre, ASICs, VCSELs, p-i-n diodes, optical
  interconnects qualified
• harnesses are not immune to SEU but the level is
  tolerable
• mechanical tolerances must be respected to
  preserve clearances
• cooling must be adequate to preserve device
  longevity
• on-sector tests at RAL will be completed before
  production begins

industrial production of 352 barrel
harnesses scheduled to begin late 2002
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