Tracker Status

August 27, 2004


Tray Assembly

-        The problem with encapsulation of wire bonds between MCMs and SSD ladders is more serious than realized last week.  It is a thermal-cycling effect that is breaking to bond between the encapsulation fill material and the dam and silicon surface.  When the encapsulation comes loose it breaks the wire bonds.  This has only been observed on trays with thick tungsten.  Remedies are under study, including consideration of eliminating the encapsulation of these wire bonds (the encapsulation appears to be a bigger risk than a benefit, and the process is difficult and time consuming). 

-        Several trays, some with silicon, some without, were put into the thermal chamber in Pisa, to receive about 15 cycles by Monday.  This is to investigate the bias circuit bonding issue and the encapsulation issue and to support the visit to Pisa next week by the anomaly review team.


Stacked Tray Testing

-        A stack of 10 trays with 19 layers of live silicon is operating in Pisa (one of the trays is the bottom tray).  Except for the problem with the thick-tungsten trays where encapsulated wire bonds broke loose (see above), the tray performance is very good.  The cosmic-ray tracks look clean, with essentially no noise.  A large number of triggers were accumulated last night, and those data are being analyzed offline.



-        286 MCMs have been delivered to SLAC.  Shipping burned-in MCMs to Pisa has been on hold for several weeks pending resolution of workmanship issues raised by the NASA inspector.

-        DPA and ultrasound is being done on two MCMs with internal bias shorts to try to understand better the failure mode.  The team is considering a higher voltage test of these nodes prior to MCM assembly to weed out any defective boards.

-        17 MCMs were carefully inspected for cracks in pitch adapters following burn-in.  Of all the cracked-trace candidates found, only a few measured to be nonconductive.  A set of MCMs was inspected and will go into 200 thermal cycles to investigate possible crack formation.  Work continues on procuring new pitch adapters without any nickel plating in the bend region, to eliminate cracking.


Flex Circuit Cables

-        Several of the flight cable panels failed coupon testing, due to incomplete connection between plating of the vias and the internal planes.  A LAT delegation is visiting Parlex today to deal with this serious issue.


SLAC Deliveries to Pisa

-        Several shipments are going out this week and early next week, including the lifting fixture, vibration fixture, inner shipping container, cable-holding frame, and EGSE systems.

-        The interface hardware will be hand carried to Pisa, including the studs of the newest design (slight change in the thread shape), which are still being coated this week.

-        The last items for Tower-A assembly, the cable-fixation corner brackets, are finished and should ship to Pisa early next week.

-        Procurement of the shipping container has been held up in purchasing, which would be a problem if Tower-A were not delayed.