Minutes of the Tracker Technical Meeting August 16, 2000 Ossie: the Si test wafers are being ground, at the same vendor that will dice the wafers. Before dicing, he needs a spec on edge roughness. The resulting roughness depends on the fineness of the diamond saw. The detector specs have never included anything on edge roughness, but the existing HPK detectors have exceptionally smooth edges. Meanwhile, the vendor will cut one and present it as a sample for us to look at. Gwelen: A new prototype of the 90-degree interconnect has been made by Alec, this time from G10 (to match better the PC board). He will have the radius cut this week and then will glue a strip of wire-bondable traces on Kapton for bonding testing. There has been some discussion of the kapton design with Pisa collaborators. Alessandro is interested in using the CERN shop and soon will make a layout and gerber file as a proposal. Robert noted that in our NASA proposal INFN is indicated as the supplier of the kapton bias circuit. Gwelen: A fresh sample of Urelane has been obtained to try out for hybrid encapsulation. Bill Rowe is making a sample PC board with dead chips and wire bonds for the initial tests. Ossie: For initial ladder encapsulation tests, Gwelen was requested to run ½ dozen rows on each of 6 samples of Si wafers already supplied by Ossie. This will not give any information on edge effects but should be good for some preliminary tests. Erik: Nothing is happening on the closeout frame design at the moment, pending programmatic decisions in progress. Preliminary drawings already are in hand for the simplified design. Hytec needs to look at venting and whether the bonding areas are sufficient. Hytec recently did some checks of plating Cu and Ni onto the recycled airline brake-shoe carbon-carbon material proposed for the closeout fabrication. Preliminarily, the results looked promising. Erik: Sidewall and core coupon testing is in progress. Mike has tested all of the YLA carbon-fiber core samples. The resulting numbers not as good as YLA theoretical specs. The density is.5 lb/cu foot vs .8 quoted. Mike finished taking data and is doing analysis to get the shear modulus and crushing modulus (through the panel thickness). Resin-based sidewall material is due in 2 weeks (the P30 carbon-carbon schedule is less sure, due to the BF Goodrich oven schedule). Some samples will be sent to outside vendors, where some tests are more cost effective. Fastener pullout tests will be done at Hytec. Steve: Hytec has selected 3 materials for facesheet samples and will narrow to 2 for tests. He got a cost quote of $232/panel for M55J (the cheapest). Our baseline cost estimates have been assuming $250. P75 (as in the existing 300um thick samples) is estimated to be $298/panel. A 6-ply layup of M55J would be 380um thick. The P75 would be about 318um thick. Use of thinner plies would substantially raise the price. Robert noted that Eric once estimated that 200um is sufficient for the thin- converter trays (and that is what was assumed in our NASA proposal). Per Robert’s questions, Erik will take a quick look at whether 4 plys could be used for thin-converter layers. He expressed concern about curling. Robert noted that if going to thinner sheets necessitates significantly more engineering study, then budget issues will almost certainly rule it out. Ossie: work is in progress on getting together a test setup for adhesives. Cleanroom work will build up soon and occupy most of his time. For example, crane installation will begin next week. Eduardo and Roman will try to pick up this work. SLAC is working on getting the test chamber moved to building 33. Gary is returning from vacation and will probably contribute to the strain-gauge work. Roman could begin working on lining up vendors and setting up orders for samples, but the PO’s must go through Ossie. Roman: his analytical model of the payload stack matches with the Hytec results now, after some help from Hytec. He is waiting on arrival of a workstation for beginning FEA. He is now concentrating on setting up test hardware at this time. He recently has configured the DAQ system for the test setup. Gwelen: He and Matt have formulated a conductivity test plan (see http://scipp.ucsc.edu/groups/glast/mechanical/Conductive_glue_testing.pdf ). The essential idea is to test Si/adhesive/gold-pad. They will thermal cycle and measure conductivity. They plan a 4-mil bond line for most tests, but will also study some with thicker bond lines. He has some info from Martin about the number of cycles for testing. Martin will put this into the thermal requirements document. Gwelen noted that humidity is known to be a big effect, in addition to temperature. Gwelen presented an analysis chip size and pad layout. See http://scipp.ucsc.edu/groups/glast/electronics/gtfe_size_recommendation.pdf It was generally agreed that we need at SLAC the wire-bonding machine and automated probing station at SLAC by the end of next summer. Robert will talk to Althouse about this. Ossie noted that he sees a need for a CNC gluing system. One could be acquired in a few weeks for some $42,000, complete with vision system. He said that this can be purchased from GPP money. Pisa will need something equivalent. Robert noted that such automation has always been foreseen, so the issue has been whether it is a commercial system or bricolage. Ossie greatly prefers a commercial system with support, and it was agreed that he should move ahead with this. Ossie: Martin claims that every tray will need to be thermally cycled. To do so, we will need a programmable system. This is a new requirement, and such equipment was not foreseen. Could this be done at the tower level? Over what temperature range is it required? Robert will discuss this with Martin. Ossie: Elliott was concerned about whether tungsten converters would self-destruct upon re-entry. Ossie researched this and found that they would not melt but should get hot enough to oxidize, ablate, and turn to dust. He talked to a tech about testing this by heating in a furnace and blowing hot air on them. Robert cautioned that he would like clear guidance from the project that the tracker is a driver in this issue before investing a lot of effort into it. Issues: 1. Should a spec on edge smoothness be added to the detector specifications document? What should the value be? 2. Standard face sheet thicknesses for standard layers are greater than what the proposal baseline assumes. 3. Does the tracker need to prove that it will break up and turn to smoke and dust upon re-entry? 4. Does component-level thermal cycling testing need to be done during production? 5. Will Pisa use adhesive application equipment similar to what SLAC will obtain? 6. Can a 4-ply layup be used for facesheets in thin-converter layers? 7. Carbon-fiber tray design is on hold pending programmatic/budget decisions. 8. Will (or should) Pisa do the flex (and PCB) work specified in the proposal budget? Decisions: 1. Ossie will order a CNC adhesive application station from GPP funds. Action Items 1. Erik: take a quick look at whether 4 plies can be used for face sheets. 2. Alessandro: make a CAD layout of the 90-degree interconnect flex circuit. 3. Bill Rowe: test the urelane potting compound on chips and wire bonds. 4. Gwelen: make 6 322-count wire-bond rows onto each of 6 Si samples and give to Ossie. 5. Roman: start taking over the task of obtaining adhesive samples for Si attachment. 6. Robert: discuss with Bill Althouse about when procurement of the assembly equipment can occur. 7. Robert: discuss with Martin requirements for thermal cycling tests at the component level.