Minutes of the Tracker
Meeting
Action Items:
- Sandro: send details on
the Plyform t-peel coupon design to Ben
- Sandro: check that the
temperature excursion did not compromise the CMM calibration
- Hiro et al: test the
tower-0 cables with MCMs
- INFN: inspect wire bonds
on EM trays that have been vibrated
- Sandro: discuss with
Plyform a procedure to passivate the cut facesheet edge on the MCM side of the tray
- Sandro: put the MIPs into the 1584 procedure and crosscheck with Plyform
- Sandro/Emilio: sign off on
documents 03566 and 00722
1) MCM connector/sidewall
clearance issue
Sandro
reported that they are working on measuring Tower-0 trays. The CMM confirmed yesterday's result. They measured the pocket depth where the MCM
mounts (i.e. the height of the thermal boss) and the connector versus thermal boss
location. On one tray the
connect protrudes beyond the thermal boss by 200um on one side and 100um
on the other. Also, the MCM is not
parallel to the closeout. After these
measurements Sandro will go to G&A to look into modifying the jig. The problem is the coupling of the rigid tool
with the tray closeout. If the tool and
closeout are not exactly flat, then the tool will ride on the highest points,
which can result in a large gap between MCM and closeout at the location of the
connectors. The depth of the pocket is good,
so that was not a significant contributor to the issue. Something that would help would be a thinner
flange on the MCM pin (from 0.3mm down to 0.2mm). Other than that, the main corrective action
will probably be to compress the glue on the connector side of the MCM. One way would be to put pins without disks on
the bottom.
2) Coupon tests of
etched/primed tungsten
Ben
reported that GSFC did the acid etch and primer on all 400 tiles, thin &
thick. They made some peel test coupons
of their own design 25cm wide. The ends
are not bonded and are bent to give something to grab onto. They were glued together with 3M 2216, with a
3-mil bond spaced with glass beads. Room
temperature cure for 24 hours, then 2 hours at 66C. The first peel results were very low. They are still trying to understand what
happened with those pieces and will do surface analysis on specimens. Specimens were made from flight tiles, bonded,
and tested this morning. The results
were 10 times better, but in all cases the failure is still the primer/tungsten
bond, not the primer/epoxy bond. They want
to investigate now bare tungsten to tungsten, for comparison. They called Cytec, who said to put the primer
on as thin as possible. Results will be available Friday or Monday. Ben would like to get from Sandro the Plyform
coupon configuration. They had tungsten
on one side, Kapton on the other. Both sides were backed up with aluminum.
Sandro will get from Plyform tomorrow the details.
Plyform
has primed their tiles and prepared coupons.
They will do the first tests tomorrow.
The old Plyform results were about 17 lbs/inch on the grit-blasted
tungsten. No quantitative comparison can
be made with the GSFC tiles until an equivalent configuration is tested.
3) Status of tower assembly
preparations & schedule
Sandro
reported that the air conditioning is back online just now. They are making measurements of the trays.
Dave cautioned that the
temperature excursion to 30C could invalidate the CMM calibration. Sandro will check this with the vendor.
Robert suggested that the flight cables in
Arthur
reported that he made shims with silicone and will use them between cables and
structural closeout walls in the Tower-0 assembly. During this process he will fill in details
for the cable installation procedure.
4) Encapsulation issue:
Robert suggested that a qual plan needs to be
formulated for trays with unencapsulated wire bonds. Sandro foresees doing a qual thermal cycle series
(12 cycles). Doing a vibration test with
a flight tray would be problematic. It
is not clean enough at Centrotechnica, and they don’t
have rigorous ESD procedures. A detector
would be likely to be broken during installation. Robert suggested, then, at least to inspect
wire bonds on EM trays, which have gone through vibration. For example, a destructive pull on each wire
just to see a non-zero strength would be enough. Tom requested that Robert send him the note
on pros and cons of encapsulation. Robert
reminded everyone that without encapsulation we have to introduce a new
procedure for passivation of the face sheet trimming
on the MCM side of the tray.
5) MCM update
- Robert reported that NASA will require inspection and some
rework of the conformal coating on MCMs.
This cannot affect MCMs already on trays, but the unused MCMs in
- Peter is working on a design of a fixture to hold a grounded flexible
connector strip (Zebra strip) against the pitch adapter while a
charge-injection test is executed. The
strip will short all channels to ground, making them nonfunctional, except
those channels that have a missing wire-bond connection or broken pitch-adapter
trace. SLAC would like to get this
system working and test all MCMs before shipping them to
6) Flex-circuit cables: Dave
reported that SLAC is waiting for cause and corrective action from Parlex. The 3rd party lab confirmed that Parlex
coupon testing was bad. Jerry is meeting
with the CEO and president of Parlex today.
7) Review of documentation
preparations for tray panel test articles
Martin
has already updated the tungsten tile drawings to include the primer and, in
the notes, the instructions for etching and priming (lifted from the TART
report).
Assembly
drawings: Sandro et al can redline them for the time being, to add the
wires. This will work for the test
articles. Martin is working on a general
update to the drawings and will include the wires.
Tray
assembly procedure: Sandro added to LAT-PS-01584 the TART recommendation for
wire and tiles, Kapton prep. He included
an electrical test from tiles to honeycomb to verify continuity. Also included is
degassing, cleaning, water-break testing, and the t-peel and hardness tests. The top/bottom tray procedure update will
wait until all the dust has settled and we are sure of the procedure. Giovanni is working the detailed procedures
with Plyform. INFN Pisa will monitor closely
the internal procedures. Sandro will put
the MIPs into the 1584 procedure. He will crosscheck this with Plyform
tomorrow.
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8) Dave said that the
alignment plan (03566) and tower assembly (00722) are waiting for Sandro’s
signature. Sandro said he is waiting for an OK from Emilio (by tomorrow).