FDC Weekly Meeting
Date: May 15, 2008
Participants: Daniel, Simon, Brian, Fernando, Roger, Bill, Mark
Next Meeting: May 22, 2008 @ 1:30 p.m.
- Roger visited Allflex in Minnesota last week and spent the better part of a day talking with the company representatives and touring the different parts of their facility. In short, they are very excited about the possibility of working with us on the FDC cathode project. Roger was very impressed with the facility and the level of cleanliness and professionalism displayed. He noted that Allflex works only with flex circuits and materials. - As a result of Roger's meeting with the sales representatives, they came up with a list of questions for us to address when preparing the PR. Each is listed with the results of the discussion from the meeting. * What degree of issue are pinholes in the material? Pinholes can occur when a speck of dust or material is trapped between the photo-resist material and the copper surface during the lamination process. While every effort is made to ensure that the copper surface is clean, these can/do occasionally occur. We feel that given all work is done in a class-100 clean room, this is the only specification that we need to provide. We are satisfied that any pinholes (on a scale of a few mils in size) will not affect the cathode performance given that we have reasonably with traces. * What tolerance/percentage of line defects are acceptable? This includes over-etched and spurious copper (under-etched) lines widths. Should we consider 5%, 10% of the width? Fernando believes that if they are willing to work to provide a 5% spec that we would be satisfied with this. * Gold-plating of the connector pads is not feasible, given the additional handling necessary and possibility of damage to the panels during the process. Allflex will investigate alternatives such as a peelable mask or an organic mask material to prevent oxidation of the connector pads. We are working to ensure that the cathode exposure to air is minimal, therefore we feel that gold-plating should not be necessary. We also felt that the inclusion of masks is not a necessity. * Automated testing of the finished panels is not feasible due to the disparity in size of their test fixture vs. the panel size. Manual testing of each cathode strip to the connector pad can be done. Note that there is no metal tie-coat that needs to be removed, so there is no issue with a dead-short panel. Our options here are obvious limited. We do require checkout of each strip on each board before acceptance. As this work cannot be done by Allflex, we will have to do the job here at JLab. Compounding the situation is that Allflex has no history with 2 micron Cu thicknesses on their boards, so we do not even have an expected probability of problems. The issue is not opens or shorts on the boards given that there is no tie coat on the material, the issue is strips with high resistances that might result from fractures or microfractures on the traces. We need to find out from Allflex what we can do if we find a board that does not meet our electrical checkout specs. * Panel-to-panel Joints - Allflex suggests that they provide us with uncut edges and we trim them in-house during our assembly process. This is of particular concern with the center section, as there is already minimal width available for their tooling and alignment holes. Our current assembly procedure relies on having a precise edge on each board so that we can butt neighbors up against each other. Roger will inquire whether Allflex could take this on and develop a procedure to leave 0.5 mm of Kapton at the joint edges of the cathode boards. * Flex Material - In anticipation of our purchase order, Allflex has ordered a sufficient amount of 2 micron material to accommodate our prototype fabrication. We discussed the possibility of JLAB purchasing a custom-made 5 micron copper Espanex material in sufficient quantity for the production run. Allflex is exploring that avenue with their associate representing the Nippon Steel Corporation in the USA. We are still very interested in obtaining samples of boards with 5 micron Cu. However, if its availability is uncertain for the short term, we will order a larger sample of 2 micron Cu boards (perhaps 10 full sets). This will leave us with extras in case of QA problems and will give us boards for testing (both Fernando and Gerard have expressed interested in performing basic checks on the boards). - Roger will work to prepare the PR, however, there are several issues that need to be dealt with. First, Fernando has reviewed the board design and has asked Roger to make some minor changes to improve the grounding layout. This work is in progress. He will recheck the boards after Roger has completed his work. Second, Bill has come up with a layout for the through-holes in the cathode boards to enable good filling and gas definition throughout the active layers. We decided that he can provide Roger with the coordinates of these holes and Roger can include them in the design. Note that Bill will update the frame drawings to include the new holes. - No progress has been made during the past week on additional solder tests of the rigid-flex assembly to the cathode board mock up. Greg Arnold's group had allegedly purchased a hot air pencil, but we found out that the order never when out because of problems with funds. Fernando will lend one for this use from the Fast Electronics Group. - Note that due to the height of the solder connection between the cathode board and the rigid flex assembly, we will have to revisit the design from the standpoint of adding clearance pockets on the surfaces that mate up against this solder region. We did find out a new option for the ends of the rigid-flex assemblies. The company can actually leave the last portion of the assembly without Kapton backing so the copper traces stick out past the end of the flex piece. This will enable easier soldering. We will have to investigate this further, but in any case, we will still have to modify the design to allow for proper clearance for the connection between the rigid-flex assembly and the cathode board. - Bill will look into ordering a storage box (called a pelican box) for the long-term cathode storage. Roger learned that the cathodes will come from Allflex shipped flat. If we can order this box and ship it to Allflex, they can use it for a delivery container. We can easily modify the box to include the nitrogen gas fittings. - Brian will modify his Lucite box design for storage of the completed cathode planes. This cathode planes can stack up on top of one another (unlike the strung wire frames). He will make some minor modifications to the existing box drawings and prepare the PR.
- Outstanding procurements for the full-scale prototype: * The HV capacitors will be delivered to us in a few weeks. * The 2nd construction station PR has not been started. Brian will get to this when he is available. * The rails (all 4-m length of them) have arrived. * The rail attachment assemblies are being worked on by Bill. He has provided a draft set of drawings to Tim Whitlatch to review. * We are still awaiting delivery of the 2-mm Rohacell for the cathode backing. While Brian was cleaning up EEL 126, he came across a box with a half dozen 2-mm sheets, so we have enough for now. - The clean tent in the EEL clean (ha!) room is now ready for us to move in. Brian will start by moving in a table and a cabinet. He will prepare a PR for two 5 ft x 5 ft granite tables. One will go into the clean tent, and the other will go into our new assembly area in EEL 126. - Brian needs to provide Casey with a drawing for the modifications to the aluminum tooling plate used for our wire plane and cathode construction. Once he does, it will probably be at least 2 weeks before we get the plate back. - Brian and Bill will work to update our wire frame construction sequence document. Brian will provide a first draft to Bill who will work to polish it up. We would like to provide this to Casey so his group (and of course ours) can full understand the procedures.
Test Frame Wire Winding
- The Phase 1 wire winding contract ended officially on Friday May 2. DSC has received a preliminary report on the status of the work, and this report will be improved by IUCF and updated over the next week. Basically they gave us what they had to fulfill the contract requirements, but it is not complete. - IUCF ended up winding 3 planes. Brian brought back two of them with him to study the transport scheme (looks like no wires broke on the 12 hour ride from Bloomington to NN). There were some problems that were found during the winding process: * The technique used to support the wire frames under the wires was non-ideal and this cause significant problems with the final wire placement on the boards. This problem was diagnosed after winding the first two wire planes. A modified procedure was used on the third plane with improved results. * The placement on of the field wires on the winding table, done after the sense wires were wound, had a minor problem. The technician did not account for the differences in wire size. Thus the wire spacing had an offset (too big on one side of the sense wire, too small on the other). This is not a real problem, and will be accounted for in future winding. * The wire placement distribution shows a fairly sizeable number of wires outside the +/-50 micron spec. The fraction of these outliers is about 10%. This is more than an order of magnitude too large. The folks at IUCF are investigating this, but believe that it may be caused by worn equipment on their wire spooling and winding equipment. * There was suspicion that the wire measurements had a correlation of where on the measuring machine the wire frame was placed. Data were taken to quantify this problem, but DSC has not gotten the analysis as of yet. * The wire tension measuring system was painfully slow, and so full tensions measurements on all wires were not completed. Kim provided the IUCF folks with the wire lengths, and they have taken hopefully sufficient tension measurement data to give us a feeling of what tolerance they can provide. We had requested +/-5%, but it may be that +/-10% is what their system can provide. We will know more shortly. * DSC will go over the Phase 1 data and meet with Elke to plan on when and if Phase 2 will take place. We need to be sure that IUCF can meet our specifications, both in terms of the detector requirements and the budget. There are rumors that IUCF is working to prepare a budget for Phase 2, but nothing has come our way yet. * Finally, much thanks to Brian who spent a long week at IUCF representing our group. - DSC is working with Steve Christo to prepare a wire specification document for the tungsten and CuBe wires leading up to procurement. Steve is preparing a document for the Hall B chambers and we will most likely adopt this document for Hall D. DSC reviewed the existing Hall B documents to give folks a flavor of how these documents have been prepared in the past. We need to make decisions on what is required for the FDCs.
Stack Assembly Procedures
- DSC, Brian, Tim, and Bill will work to finalize the stack assembly construction document that has been prepared. This document should be in place before we get too far in the construction process.
Composite Cathode Updates
- Denny has extracted the tensioning system from mothballs and it is now being setup in the shop. Brian will work to make a tensioned cathode without foam backing on his return. In tensioning the cathode plane he will study how the 3 piece cathode reacts under tension. He will also measure the electrode distortion as the tension is increased. - The cathode tensioning work has been delayed due to a miscommunication between us and the shop on what was to be done. As the instructions Casey had received were not complete, DSC put the work on hold until all necessary equipment for the measurements was in place. Brian will be directly involved in all aspects of this work. - Denny has the Acquity Laser system from Fernando and has it fully set up trailer 94B. He has done some test measurements and verified that the measurement results agree with crude measurements. Bill completed the PR for the laser and it is now ours. Denny is modifying his setup to provide a more robust support frame for the cathode frame and is incorporating the ability to do 2D measurements with the system. DSC will push Denny to provide 1D measurements of our prototype cathodes down the middle so that we can understand the gravitational sag scale of the cathodes with the 2-mm thick foam backing. - David Lawrence will be supervising a high school student for the summer. This student will work on taking Denny's flatness measuring system and automating it to do full 2-D scans of our cathodes. This student will be arriving in the middle of June. - Fernando has indicated that he is worried about the quality of the cathode ground if we only provide a connection through the 10th daughter board. He has asked that we work to include additional ground connection points about the cathode perimeter. We have to look into this. One suggestion that came up was to make the cathode support frame a PC board (a simple one) that we could connect to.
Cooling System Tests
- Denny completed the set up of the cooling system. He then packed it up and will move it to F117 after the system review. Fernando will take over the measurements and study the cooling properties with a fully loaded preamp daughter board in place.
Gas System Design
- Vladislav (Slava) Razmyslovich is working on a preliminary layout of the gas handling system for the CDC and FDC in preparation for the upcoming systems review. We will sit down with him in a specialized meeting to review the design concepts when we get a chance.
Gas Volume Definition
- Bill has put some time into moving the design forward and the main points are given earlier in the minutes. Basically as the gas fills the volume like a liquid, he wants to include a series of holes in the cathode about the full perimeter of the board. This will require modification of the support frame (the G10 skin onto which the cathode is mounted) to allow for the gas to go through the G10 and the foam core. Note that any foam exposed to the gas must be sealed.
- Kim needs to provide an instructional writeup for the Phase 1 and Phase 2 wire frame PCB component attachment. This is on her to-do list, but is not a high priority for now.
Cathode Board Discussion
- Roger needs to prepare a document for QA/stuffing/cleaning for the cathode boards and a similar document for the cathode daughter boards and ground boards.
- Work continues on characterizing the preamp daughter boards to specify the ASIC dynamic range for both the FDC cathodes and wires. Simon is extracting from the data the amplitude distributions. In detail, he is extracting the peak voltage amplitude from each FADC distribution. Sample results are in the FDC log book for the cathodes and the anodes. Knowing the gain of the ASICs, cables, and shaper (in fC/mV) we can work backwards for the muon data to specify the dynamic range. We can then specify the dynamics range for the more heavily ionizing protons and (more importantly) pions in the FDC chambers (know the difference in energy loss in the FDC for these different particles). Fernando will characterize the gain of the ASIC/cable/shaper combo for us in his lab. Simon is also working with simulations to try to come up with a cross check of the dynamic range that we extract from the data. For this, he is working with some advanced features of GARFIELD that model the ionization and clustering. - Simon, Fernando, and DSC will prepare a write-up of the analysis results and our analysis of the required dynamic range of the anodes and cathodes. Fernando will be in contact with Mitch Newcomer on our progress and plans. Our goal is to have a first draft of a report on this work by the end of next week. After the systems review, we will spend a few days to polish up the report and circulate it to a wider group for comments before passing the information on to Mitch. - Note that as we need to characterize the ASICs for both the FDC and CDC, it may be beneficial to the project for Yves to visit us from CMU to go over the measurement results and connection from the data to the final specification of the dynamic range. It is not clear when this visit would be most useful. Things will come into focus over the next several weeks. - Note: it is apparent that we will not have completed our work on the characterization of the ASIC dynamic range before the next submission deadline to MOSIS. However, it seems that we will have another submission opportunity later in the summer. This should not delay us too much - Brian will perform an optical scan of the cathode strip edges in one of our spare 2 micron Cu cathode planes. We want to make sure that there are no obvious systematic problems with the construction. He will work to find a x50 microscope to do this work.
- DSC has collected all of the available FDC subsystem design drawings and placed them on the FDC website. The URL is: http://www.jlab.org/Hall-D/detector/fdc/drawings.html. Folks should go through the drawings and let DSC know what drawings and/or categories are missing for a complete design set. - Also folks should send DSC the latest design drawings where there have been changes to keep this web site up-to-date through the review season.
- The FDC short-term work list has been posted on the FDC web site (see http://www.jlab.org/Hall-D/detector/fdc/). This is continually being updated and DSC welcomes any feedback or comments from the group.
Minutes prepared by Daniel. Send any comments or corrections along.