GLAST Proposal Review

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GLAST Large Area Telescope Tracker
Subsystem WBS 4.1.4 Highlights in Progress Since
the January Review Robert Johnson Santa Cruz
Institute for Particle Physics University of
California at Santa Cruz Tracker Subsystem
Manager johnson_at_scipp.ucsc.edu
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Outline

• Overview
• Results from January Review
• Action Item Status
• Changes Since January Review
• Hardware update since January
• Schedule and Cost
• Summary

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Tracker Overview

• 16 layers of tungsten converter foils.
• 12 layers of 3 X0 converters
• Followed by four 18 layers
• x-y Si-strip detector pair closely following each
  converter foil.
• Two additional pairs at the bottom are needed for
  triggering.
• 19 stiff composite tray panels support SSDs on
  both faces with electronics on two sides.
• Converters are on the bottom face, just above the
  SSD plane
• 2-mm gap between trays
• Carbon-fiber sidewalls conduct heat to the base
  and stiffen the module.
• Electronics are based on 2 ASICs, PC boards, and
  custom flex cables.
• 31.6 kg mass per module.
• 10.5 W of power per module.

Multi-Chip Electronics Module (MCM)
19 Carbon-Fiber Tray Panels
Carbon-Fiber Wall
2 mm gap
Readout Cable
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Tracker Production Overview
Module Structure (walls, flexures,
thermal-gasket, fasteners) Engineering SLAC,
Hytec Procurement SLAC
SSD Procurement, Testing Japan, Italy, SLAC
SSD Ladder Assembly Italy
10,368
Tracker Module Assembly and Test Italy
2592
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Tray Assembly and Test Italy
342
342
Electronics Design, Fabrication Test UCSC, SLAC
Composite Panel Converters Engineering SLAC,
Hytec, and Italy Procurement Italy
648
Cable Plant UCSC
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Results from January PDR/Baseline Review

• The Tracker has an Experienced Project Team .
• The concept of the Tracker is well matched to the
  science goals and utilizes mature technology.
• The design is well thought out and can be
  implemented within the available time.
• A strong consortium of groups in Italy has taken
  the responsibility for assembling and testing all
  the ladders, trays, and towers. This is a crucial
  contribution to the Tracker which is being
  executed in a very effective and competent
  manner.
• Baseline the Tracker with Increased Contingency

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Action Item Status
Action Item Response
1 Baseline the Tracker with Increased Contingency The current basis for estimating Project contingency needed uses 25 of the Tracker cost to go VS 18 in January
2 Thoroughly evaluate pre-production ICs Agreed Plan in place
3 Refine Assembly and Test Procedures Agreed In process
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Changes Since January 02 Review

• The schedule has been revised to accommodate the
  overall LAT schedule extension.
• Added time for additional ASIC submissions.
• Incorporated a more conservative schedule for
  Tracker module production with the Italian
  groups.
• Critical Deliveries
• Modules 3, 4 available March 29, 2004, with 11
  weeks of float.
• Modules 15, 16 available August 4, 2004, with 7
  weeks of float.
• Budget
• Estimated cost at completion increased 180K
• MOA with Italy
• INFN ready to sign and has been providing the
  requested funding and covering for the delay in
  ASI approval.
• ASI has not yet signed but has recently begun
  funding Tracker work with approval of 800k for
  FY2002.

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Prototype Tower Module

• Mechanical prototype loaded with dummy SSDs.
• Includes flexure interface to the Grid.
• Used to test and evaluate assembly methods.
• Assembly worked well, but tray tolerances were
  not quite to specification. Tray assembly
  tooling has since been revised and specifications
  met.
• Vibration and Thermal testing
• Single panel LAT-TD-759. ?
• Grid-to-tower interface thermal cycle report in
  progress. ?
• Random vibration of the full module LAT-TD-788.
  Problems (see following)

Composite trays and mass models of the prototype
tower, before mounting of the sidewalls.
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Vibration Test Problem 1

• Some screws attaching the sidewalls to the bottom
  tray backed out during transverse-axis
  qualification-level random vibration. This
  problem was solved (as verified in a retest)
• Replace hex heads by Torx-Plus to enable
  tightening to the full specification without
  stripping the heads.
• Double the number of screws in the non-MCM sides
  of the bottom tray.
• Add aluminum washer-inserts to the sidewalls for
  these fasteners.
• We also plan to use a secondary locking mechanism
  for the screws in the final assembly, as extra
  insurance.

Full module instrumented for thrust-axis vibration
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Vibration Test Problem 2

• In the first test, a hairline crack formed in the
  bottom-tray closeout between the edge and a
  corner-flexure fastener.
• In the second test suite at transverse-axis
  qualification levels the cracking increased and
  the problem propagated to all 4 corners, breaking
  loose the corner-flexure mount inserts. (The
  mid-span flexures all held fast.)

• Remediation in process
• Analysis to make sure we understand the failure
  and the cure.
• Remove light-weighting cutouts in the bottom tray
  and increase its height by 5 mm.
• Reinforce each corner with a bonded metal
  bracket.
• Remediation Plan presented to Project ART.

Cracking as seen after the second test suite.
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Tracker ASICs

• The second run of the GTRC and GTFE ASICs needed
  to be resubmitted
• GTRC V2
• Missing rule in the Tanner DRC led to a short in
  the memory.
• Although complete chip was simulated with
  Synopsys Timemill, clock skew margins were not
  sufficient for the IC to function at nominal
  supply voltage (Tanner does not extract the clock
  network as a distributed RC network).
• GTFE Vf a minor modification was not verified by
  simulation due to misunderstanding, missing an
  error that removed the baseline restoration.
• GTFE Ve the same missing DRC rule led to a
  nonfunctional analog chain.
• Remediation
• Careful crosscheck of the DRC rule-set against
  the Agilent vendor rules and use of the MOSIS DRC
  checking service.
• Improved pre-submission procedural control.
• Controlled row-wise clock routing in the GTRC
  core.
• Submission of a back-up GTRC version without RAM.

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Tracker ASICs

• The digital section does function in the GTFE Ve
  Vf chips, allowing substantial testing to
  proceed
• Probe-card testing of the GTFE using the full set
  of test vectors developed according to
  LAT-TD-247.
• Testing on the mini-MCM using GTRC V1 chips.
• Several problems were addressed in the versions
  in production
• Proper response in the GTFE to undefined
  op-codes.
• Logic errors in GTFE register loading.
• Protection resistors in the I/O pads led to
  unreliable operation at the full 20 MHz.
• Clock skew issues in the GTRC.
• DRC errors and the GTFE Vf comparator bug.
• Chips presently in fabrication (Due August 22)
• GTRC with custom RAM and GTRC with Flip-Flop RAM
  (both usable for flight).
• AC and DC coupled GTFE versions.

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Electronics Testing

• Several mini-MCMs are under test at UCSC and
  SLAC, using the V1 GTRC and Vf GTFE chips.
• Using COM card, interface board, and Python
  script at UCSC, to develop the test station for
  MCM production.
• Using 2 COM cards, TEM, and SCL script at SLAC to
  debug the ultimate readout scheme.
• Mini-MCM has been interfaced with flight like
  Tower Electronics Module(TEM) to verify
  functionality and interfaces. Continued use for
  hardware and flight software development.
• Parts qualification is in progress for
  poly-switches and HV caps.
• Planning is in progress for radiation testing
  (total dose and FEE) after the new chips arrive.

A mini-MCM loaded with 2 prototype front-end
chips and 1 controller chip.
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Electronics Test Systems

• GTFE wafer probing
• Operational on a manual probe station (undiced
  wafers will be available end of August).
• Thorough set of test vectors for complete
  functional testing (see LAT-TD-247).
• All of the test vectors have been exercised
  through the simulation and actual chips (which
  uncovered the bugs fixed in the present
  submission).
• GTRC wafer probing
• Complete hardware and software for manual
  testing.
• Thorough set of test vectors (see LAT-TD-248).
• No bare die yet to test it on (probes dont fit
  V1).
• Test vectors are presently being exercised
  through the simulation and on the mini-MCM (with
  some restrictions, such as not being able on the
  mini-MCM to cycle through the address space).

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Electronics Test Systems

• MCM testing during production at Teledyne
• Second-version interface board is in hand with
  enclosure plus a better monitoring interface for
  power supplies and LVDS bias levels.
• Test plan documented in LAT-TD-153 and
  LAT-TD-249.
• Test vectors are under development for functional
  testing, based on extending the GTRC set.
• VME ADC modules were obtained, and software is in
  progress to test the power supply voltages and
  the LVDS driver bias levels.
• Some software has been developed for threshold
  scanning (analog performance tests) and tested on
  the d-version chip.
• Basic system, to be operated by its developers,
  will be ready for testing the engineering-model
  MCMs in September.
• MCM burn-in station layout of special cables is
  in progress.

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Electronics Production

• Teledyne has successfully developed and tested
  the tooling for bonding the pitch adapter flex
  circuit onto the MCM PWB.
• All parts and materials are present at Teledyne
  to begin assembly of the dummy MCMs for the
  mechanical/thermal engineering model tracker
  module. These modules will have all parts, but
  with dummy or bad (GTFE Ve) ICs and with some
  capacitors replaced with resistors to mimic the
  IC heat load.
• All of the molded plastic MCM carrying cases are
  in hand (in fact, in sufficient numbers for the
  flight build). These are used for MCM testing
  and burn-in following assembly, as well as for
  storage and transport.
• Assembly of the dummy MCMs is beginning at
  Teledyne.
• Pisa is testing the MCM-tray interface,
  especially with thermal cycling.

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Engineering Model Tooling Production

• Experience with the prototype Tracker module led
  to many detailed changes in the assembly tooling
  designs for trays.
• Plyform (Italy) is now assembling EM composite
  panels with the new tooling, and work is
  beginning to add the converters and bias
  circuits.
• GA Engineering (Italy) has assembled all of the
  dummy SSD ladders and is now working on the live
  ones, expected completion July 30, 2002. The
  electronics test system for the ladders is
  operational.
• Tools for mounting the ladders and for assembly
  of the top/bottom trays are in progress.

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Procurement of Long-Lead Items

• Silicon procurement and deliveries on schedule.
• 2314 HPK SSDs have been received and tested in
  Italy.
• Production of flight SSD ladders will begin as
  early as August 5, 2002 pending ladder assembly
  procedure review and release.
• The carbon-carbon closeout material is on order
  from Alcomp (US).
• In purchasing some items for the EM sufficient
  quantities for the flight build were ordered to
  reduce costs
• The molded MCM carrying cases.
• All of the screws for sidewall attachment.

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Summary Schedule
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Key Milestones
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Cost Commitments
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Cost Profile
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Workforce Plan
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Summary

• The flexure-mount redesign effort is on schedule
  and should not delay the Engineering Model
  schedule or the CDR.
• All other aspects of the Tracker design are
  complete. All lowest-level drawings are in place
  as drafts, with 22 released. Good progress on
  assembly and tooling drawings. See the drawing
  tree on the Tracker web page.
• Some details of the production fixtures and
  processes are still being tweaked and tested as
  the Engineering-Model build progresses.
• Work is accelerating on documentation of test
  plans and processes and production processes, in
  preparation for CDR.
• Overall, the Tracker development is progressing
  on schedule for the subsystem CDR in January 2003
  and the LAT CDR in April 2003.