- The Anomaly Resolution Team (ART) spent the week in Pisa and at Plyform and concluded with a report that makes a number of recommendation on how to assure good and reliable bonding of the Kapton bias circuits to the trays. The two most important process changes recommended are
1. Acid etch and prime all of the tungsten foils on both sides before beginning assembly. This is already being pursued both by a Plyform subcontractor and by the NASA GSFC plating lab. The first etched foils could be available as early as next week.
2. Add a thin compliant layer between the steel jig plate and the bias circuit while clamping in the vacuum bag, in order to distribute the clamping pressure more evenly.
- In addition, the ART made a number of recommendations on how to maintain cleanliness and how to monitor the process, and they outlined a test and qualification plan to be followed. The Tracker team is working aggressively to implement the recommendations.
Several trays, some with silicon and thin tungsten,
some without silicon, completed 14 thermal cycles at atmospheric pressure in
- The failure of encapsulated wire bonds between MCM and SSD is completely restricted to the heavy tungsten trays. Hundreds of wire bonds broke on both sides of the heavy trays during the initial 4 thermal cycles, whereas absolutely no wire bonds suffered such failures in the thin-tungsten trays. The only viable way to avoid this problem appears to be elimination of the encapsulation between MCM and SSD (this is not an unusual configuration—most silicon detector systems avoid wire-bond encapsulation, including the large space-born AMS system).
- Plyform reworked two of the failed trays, including the top tray, so that they can be used in a trial tower assembly (see below).
- Plyform restarted production of bare tray panels. We are planning our recovery with a goal of including tungsten and bias circuits in the production by the beginning of October.
Stacked Tray Testing
A stack of 10 trays with 19 layers of live silicon continues
to operate reliably in
- Jumpers and interconnect boards are on order to equip the remaining 3 stacked tray testing systems.
- The layup was completed before the August break.
- Coupons have been pulled, but the Tracker team doesn’t have the data yet.
- A set of solid aluminum sidewalls were machined and verified by CMM to validate the machining program. The results were very good.
- Several meetings were held on MCM workmanship issues. See the minutes on http://www-glast.slac.stanford.edu/Tracker-Hardware/Minutes
- Work continued on understanding bias shorts in MCMs. In almost all cases where the shorts were not there from the start they formed during the thermal cycling and burn-in. Plans are being formulated to high-pot the boards to isolate those with defects.
- Supplies of some production items are critical, especially the pitch adapters. SLAC is
Flex Circuit Cables
- Progress was made on getting GSFC and Parlex together on resolving the coupon test issues. A 3rd party lab will evaluate the GSFC and Parlex coupons to resolve the dispute.
- We have 7 of 8 cables with good tested coupons, with only C4 missing. Parlex has C4 cables ready to ship, so if their coupons test good, then we will be all set for Tower A.
Misc. SLAC Deliveries to INFN
The lifting fixture is in
- The last items for Tower-A assembly, the cable-fixation corner brackets, had to go back for some rework, so they won’t ship until next week.
The interface hardware will be hand carried to
- The Tracker team is preparing to do a trial assembly of a tower from the existing trays (some without operating silicon) the week after next. All trays will have MCMs, so the resulting tower can go through the full suite of functional testing. The tower will be disassembled following the functional tests. This process will help to get the remaining processes finalized and the bugs out before assembly of the first flight tower.