Minutes of the Tracker Meeting
- 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.
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).