Tower A:
- The assembly and metrology are complete, and the tower is at Alenia. No damage or loss of channels occurred during the transportation.
- Tower A completed vibration testing on the z axis today and y-axis vibration is in progress. All vibration testing will be completed tomorrow.
- During assembly and test, some wire bonds were broken within the MCM and between SSD wafers in some ladders, due to encapsulation failures. However, >99% of the active silicon area of the tower is functioning properly, and the overall layer hit efficiency for cosmic-ray muons is close to 99%, well within requirements.
- See http://glast.pi.infn.it/TowerA.html for some views of the assembly and cosmic-ray events, as well as maps of the inefficient areas.
Tray Assembly:
- 2 Tower-B completed trays are in
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- 8 completed tray panels were received from Plyform this week. Plyform is still working with
- The Tower 0 heavy trays are being thermal cycled some more to try to understand better encapsulation failures on ladders, which occur only on the highly asymmetric trays, namely the bottom tray and the heavy converter trays.
- The project is considering raising the minimum Tracker test temperature from -30C to -20C to alleviate the encapsulation issues.
MCMs:
- 134 flight MCMs have been fully tested and inspected and shipped to INFN.
- Conformal coating rework, testing, and inspection continue on the existing stock of MCMs at SLAC. Another 25 should ship out today.
- A special clamp and procedures were obtained to rework MCMs with small delaminations of the pitch adapter, so this work should start soon.
- A NASA “Tiger Team” visited SLAC and Teledyne last week to study and advise on MCM production and quality issues. The team concentrated on the encapsulation failures that afflict MCMs delivered starting in early July and result in scrapping at least 16% of the existing stock.
- Silicone contamination from masking tape is being studied as a possible root cause of the encapsulation failures. Other thermal issues are also being studied. Work is in progress on a cover to protect wire bonds in case the conclusion is that the encapsulation cannot be used.
- The
- SLAC has a new source inspector trained and ready to go to Teledyne for the production. With many lessons learned, the inspection and oversight will be much more effective, to keep on top of all the quality and technical issues.
- The attempts to solve the pitch adapter trace cracking issues did not work out for various reasons, so production will continue as before, with SLAC absorbing the yield loss. A second vendor of pitch adapters is being qualified on essentially the same design, with some hope of getting a more reliable product.
Flex Circuit Cables:
- More work is being done thermal cycling some cables. One cable with good coupons survived intact 100 cycles. We are cycling two more cables to work out a plan for acceptance thermal testing of cables.
- Parlex and GSFC have perhaps found the root cause of the via plating problems. 6 panels are being fabricated now to prove the process with a new cleaning step.
- SLAC is holding weekly meetings with Parlex on a series of action items designed to resolve the outstanding quality issues.
- The NASA Tiger Team plans to visit Parlex next week.
- First article cables made up from two spliced parts arrived yesterday from Cirrex. One is being assembled, and a series of tests are planned.
- First article full-size 1-piece cables from a second vendor are expected before Christmas.
- We are delivering some prototype cables to Zentek to qualify them as a cable assembly house.
EMI/EMC Testing:
- Fixtures were ordered to support EMI/EMC testing of Tracker towers after delivery to SLAC.
- Good progress was made on defining the EMI/EMC test plan and writing detailed procedures.
Parts:
- Efforts are in progress to inventory all parts and order spares, taking into account new knowledge on yields plus loss of the parts used in Tower-0.
- Orders are being made for additional quantities of some long-lead items, such as carbon-fiber prepreg and carbon-carbon blanks.
- The latest order of GTFE chips was inspected and delivered
to Teledyne, and one mini-MCM with these chips was sent to
- There is concern that we may have to procure more ASICs; we are working to get an accurate updated inventory of parts at Teledyne.