Minutes of the Tracker Meeting
November 14, 2002
Sandro reported that he was at Plyform yesterday. There they have a slow rate of panel assembly still. One problem is that there seems to be a narrow range of pressure that will work for the sandwich assembly and it is time consuming to optimize it. They have found that 0.2 atm is too low for a reliable bond, while 0.4 atm is too high and can cause some damage. Another problem is that the cores have to be cut down to size in the lateral dimensions because of past changes in the closeout thickness. 3 panels will be finished this week. Sandro is asking them to do 4 next week. Then another 4 the week after that will finish the EM standard trays.
Material and drawings went to the machine shop from Plyform to make the closeouts for the top tray. The tool to mount tungsten is ready. The Kapton tool needs one more piece glued to it. Sandro plans now to start mounting tungsten and Kapton the last week of November (was Nov. 11 in the minutes from 2 weeks ago). In that case in principle G&A can start mounting ladders the first week of December.
Tom is ordering 25 heavy cores for the bottom tray. This will be enough for the EM and flight. The point is that we are changing the bottom tray design to use heavy core and 6-ply face sheets. Thicker face sheets requires slightly thinner core and slightly shorter closeouts, so those drawings have to be updated. There is 100 microns difference between 6-ply and 4-ply thickness, according to Sandro. Tom proposes to order the cores unexpanded and machine them ourselves to a precise thickness. Then they can be expanded by returning them to the vendor or maybe by Plyform. This appears to be the only reasonable way to achieve the tolerance at a good price. Sandro will ask if Plyform can expand cores. Note that the core has to be cut to the final lateral dimensions after expanding.
Sandro reported that G&A has built a jig to test wire bonding from MCM to tray and is working on encapsulation. Results are expected next week for both. They produced 30 ladders and 20 have been tested electrically, with good results. The maximum leakage current was 700 nA, with the average about 400nA.
Sandro will go to Mipot with the new encapsulation material to get them started on that. In December he will send wafers to Mipot to make 100 flight ladders there. We will need a preproduction review at Mipot. Tom suggested to do the follow-up at G&A at the same time and also the PRR for Plyform. Sandro says G&A will probably be ready next week to start encapsulation. Mipot will be later, but probably the PRRs for Mipot and for Plyform can be held in the same week.
Tom said that he sent enough extra tungsten for 3 trays. Robert said that it has been decided to put tungsten on the 3 highest trays in the mini-tower. Also, the extra tray to be made for qualification testing should have tungsten.
Next week they will start thermal tests in Terni, first with tray boxes and then with 2 trays in the boxes.
Tom will go to Italy next week and will bring CV15-2500 (500g), CV1142 (6 3-oz tubes), CC for the bottom tray, conductive metal tape for sidewalls, and 3 rolls of transfer tape for MCMs (a regular Santa Claus!). He will try to get Teledyne to send some dummy MCMs to SLAC in time to take them as well. The insert bonding tool is done but is heavy. The assembly tool will be done by Friday. It is even heavier, so he plans to ship those items.
The functional MCM assembly work hit a couple of snags this week. Mostly they are our fault. We put the wrong width of raised strip along the edge, so Teledyne shipped the boards back to SLAC to be corrected. New pieces are ready to bond in place to fix that. SLAC will also countersink the screw holes for the connector mounting. Also, the ICs were diced larger than expected, and they are now larger than the gold pad on the PWB. This makes it difficult or impossible for the robotic tool to place the chips on the board.
Ossie reworking the MCM/ladder assemblies to shift the MCM over by one half chip. Those will go to UCSC to get MCMs mounted on Friday.
Erik announced that Steve Spencer is joining Hytec and will be helping with the GLAST project.
The IPO has agreed that we should proceed with the design just to increase the strength of the interface to the Grid such that nothing breaks with the GEVs input levels. We do not need to concern ourselves about displacements at those levels. The old coupled loads analysis (CLA) from a year ago indicates no problems with displacements. A new CLA and an acoustics analysis in progress will give the inputs needed for analyzing displacement. Until those are available we will proceed under the assumption that the displacements are okay. Erik said that he will look at Tim Thurstons report and propose definitions of margins to be used in the design effort.