Difference between revisions of "Minutes-8-23-2012"

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== Cathode corrosion ==
 
== Cathode corrosion ==
  
−
- New SEM results from Olga (follow the above link) for the samples from the Vlad's test with the vacuum chamber; the chamber had water inside and temperature at end of the day (lamps were off overnight) was close to 100degC.  The test was done for about 4 days.
+
- New SEM results from Olga (follow the above link) for the samples from the Vlad's test with the vacuum chamber; the chamber had water inside and the temperature at end of the day (lamps were off overnight) was close to 100degC.  The test was done for about 4 days:
  
−
=*Copper foil with EPDM inside: significant corrosion, a lot of sulfur present.
+
*Copper foil with EPDM inside: significant corrosion, a lot of sulfur present.
 
   
 
   
−
=*With the EPDM of the gasket part of the foil strips were inside the gas chamber and part exposed to the air: no sulfur seen at the air side and a lot of it at the gas side. However, inside the gas volume there was moisture and the temperature was much higher than outside. We had seen corrosion before also in the samples placed in air with some water put on the foils and no heating.
+
*With the EPDM of the gasket, part of the foil strips were inside the gas chamber and part exposed to the air: no sulfur seen at the air side and a lot of it at the gas side. However, inside the gas volume there was moisture and the temperature was much higher than outside. We had seen corrosion before also in the samples placed in air with some water put on the foils and no heating. We will do more tests.
  
−
<!--
+
*Copper foil with Viton: some traces visible, almost no sulfur there but some chlorine. Tim suggested cleaning the O-rings before installation.  
−
 
+
−
- Results from the vacuum chamber (Vlad's) experiment: it was running from last Thursday (end of the day) till Monday morning, pictures linked above. One clearly sees damages on the EPDM sample, just a little on the Viton one and no damages are seen on the Viton+grease sample. The samples are now with Olga and will have SEM results next week. Bill proposed to make another sample with Viton+grease with curving shape to have more potentially damaged area and then measure if the resistance has changed. Vlad will check the resistance of the samples that we have now. On Tuesday we started the same test except there's no water inside the gas volume.  
+
  
−
- As of now we see two solutions of the corrosion problem: using the technology that we used already for the third and fourth packages, i.e. Viton+grease, or in addition to that, covering big areas on the cathode including all the traces with Kapton glued with Hysol. Using Kapton foils doesn't seem to create leakage but we tested this on a flat Lexan sheet. We decided to use the standard technology for the second package, i.e. only Viton+grease. When we come to the first package (in about two-three month from now) we will discuss again the use of Kapton; there we may have to use it if we are going to re-use the cathodes from the former second package since some of the channels have to be fixed with conductive ink. Of course we will wait for the latest SEM results
+
*With Viton and Apiezon: no visible corrosion, only copper and carbon lines are visible, but the grease was not cleaned. Olga will repeat the measurements after cleaning it.  
−
before continuing with this procedure. Note that one once you chose one of the two options you can't use later the other one, like you can't use epoxy if the surface is greased.
+
  
−
== Conductive tape technology ==
+
- The first testing chamber with production wire frame and cathodes was opened yesterday, exactly 4 weeks operating with HV and gas. Some traces from the EPDM O-ring are visible but it doesn't look like the corrosion on the first and second packages. We conclude that the humidity is an important factor. No traces on the cathode against the Viton+Apiezon O-ring are visible. The test with the small-scale prototype is running two weeks, haven't opened it yet.
  
−
- Microscope pictures from the damaged cathodes (package one) on which we have removed the rigid-flex assemblies (or daughter cards) are linked. On the card contacts one can see the silver balls, on the foil contacts the conductive tape is visible with some balls inside and also on the copper pads (the cathode side). We found it is important to count the number of dents (craters) on the copper pads after removing the conductive tape with heating and cleaning the place. Vlad did this for one full cathode. First he measured the resistances on all the channels, then the cards were removed and then he did the counting by classifying the craters roughly as big and small (factor of 2-3 in diameter). The distributions of the big/small/sum of the two are Poissonian with a mean value of the sum of ~5. By correlating the conductance (1/R) with the number of the balls one can estimate roughly that a big ball has about 1.2 Ohm on average and a small - ~3 Ohms. Then some correlation is visible between the conductance and the weighted sum of the number of the balls (first three histograms, in linear, log-y scale and as a profile). There are of course errors in counting the balls, but in average for most of the cases the resistance can be explained by the number of the balls, i.e. statistically.
+
- Tim for the humidity conditions in the Hall: nominally it will be less than 45%, but he can't exclude some periods when it might be higher. There will be dry air blowing through the magnet. We should avoid opening the Hall doors for a long time during the installation.
−
 
+
−
- Another important result: all the first test samples using conductive tape technology were re-measured. On the first 8 cards all the channels showed resistance below 2 Ohms, and most of them being 0.6-1 Ohm. Among these ~half were with tinned card contacts, four were irradiated with ~1-10KRad, one was cooled with liquid Nitrogen. The last card (no special treatment) had many channels in the 10-100 Ohm region. When the samples were made we checked them with a testing card which tells you only that there's conductivity, we didn't measure the resistances. We suppose the last card was not glued correctly from the very beginning. These samples were made Feb-April 2011.
+
−
 
+
−
- We conclude: most likely the variations in the resistances we  observe on the production cathodes are due to mechanical deformation of the cathode frames. The samples were made on small g10 plates and when handling them you don't have the leverage to deform them. The cathode deformations, both pringling and radial deformation may cause curvature at the contacts which can move the balls from their position.  
+
−
 
+
−
- We discussed if (1) we are going to continue with the same conductive tape technology but making sure the cathode doesn't deform after the cards are glued to the cathode, or (2) we use conventional soldering or a new technology for bonding the contacts. After long discussions we decided to go with (1). Bill: not comfortable with the current procedure (actually nobody is), but making sure the cathodes don't move should help. Eugene: this question had to be discussed five years ago, now we should continue with the conductive tape technology, even if it turns out say 10 channels are not working it will not be a problem. The main argument to use the conductive tape is that you can repair it (Simon) or fix several channels using wires (Anatoly demonstrated that's possible). On the other hand, once the cards are soldered you can't re-solder them, although fixing some components on the cards is also possible. New technologies, cathode designs (Bill) were discussed but all these require at least a lot of R&D, followed by complete refurbishment of the cathodes and we are not in a position to do this now.
+
  
 
== Engineering ==
 
== Engineering ==
  
−
- Discussions how to make sure the cathode stays flat during all the operations after installing the conductive tapes, which includes: gluing the cards to the back of the cathode frame, moving the cathode from one place to another, storing the cathodes, cathode installation in the package, colling tube installation, testing the cathode channels, connecting the cables to the cards.  
+
- We will have two strong-backs to be used to grab the cathodes from both sides and keep them flat. We discussed how to support the cathode periphery when using the strong-backs. Casey made a table with rods that will be used to store the cathodes in a flat position.
  
−
- After the meeting Bill, Dave, Lubomir and Casey discussed these issues at Blue Crab. Bill will make two strong-backs (lifting frames) with suction caps (use vacuum), to be used on the foil or the back side of the cathode for transportation. Casey will work on a table with rods to store the cathodes in flat position. Same clips that are used for grounding will be put on both sides of the cards attaching them to the wire frame, which will prevent radial deformation during tube installation, cabling and testing.
+
- The rings for the cathode strong-backs came from the REX company right after the meeting, but there were issues with the fittings for the suction cups; also the weight of the aluminum ring seams too big.
 +
   
 +
== Electronics ==
  
−
- Bill: Mylar gluing problem we had recently is due to humidity. Several tests were done showing much better results when using lamps for heating. Bill suggested using lamps from now on the improve the curing process.
+
- Fernando: wrong zip file was send to the company for the PCBs; now all the files have the correct names to exclude such a problem.  
  
−
== Electronics ==
+
- Main discussion was what to do the with these four PCB sets. Mechanically, compared to the original PCBs, there is a small difference in the gas connector positions (about a mm); according to Tim it will work and mechanically the wire planes will be interchangeable. Fernando: some of the signal traces are at different positions and the gold-plated ground area is bigger; the traces going through that area have to be covered with conformal coating. There should be no differences in the HV PCBs, but Fernando will check all the boards and on Monday we will decide if these can be used. Eugene: if you spend more than two weeks on these boards we better purchase new ones, which however will be tricky (at the end of the fiscal year) and will delay the production. Lubomir and Dave: we will need the boards in two weeks, if not we have to re-work the schedule.
−
 
+
−
- It turned out wrong Gerber files were used for the production of the extra 4 PCB sets ($9K). Eugene will discuss with the administration how to exclude such mistakes in the future; he suggested manufacturing another 4 PCB sets.
+
  
 
== TDR ==
 
== TDR ==
  
−
- Lubomir: the version linked above is almost complete; just sub-system section needs more work. Everybody is encouraged to make his remarks.corrections by the next meeting.
+
- Lubomir received corrections from Bill and Simon, still some work remains to be done here.
  
 
== Other ==
 
== Other ==
  
−
- Beni asked when the third package will be in 126 for testing. Need to install the grounds, all the parts are ready, Vlad will start working on that, then the cooling tubes have to be installed and finally Chris will do the HV connections - in about 2 weeks must be ready.
+
- Eugene urges us to do all the purchases for the FDC as soon as possible at least by the beginning of September; after that most likely there will be no money till the end of FY12.
−
 
+
−
-->
+

Latest revision as of 16:35, 24 August 2012

August 23, 2012 FDC meeting

Agenda

  1. Production Construction Tracking (Dave)
    • Cathodes
    • Third package
  2. Cathode corrosion
    • Results from SEM analyses: [1]
    • Test chambers
  3. Engineering (Dave)
    • Cathode strong-backs
  4. Electronics (Chris, Nick)
    • PCBs
  5. TDR, pages 132-145 (Lubomir)
  6. Other

Minutes

Participants: Fernando, Tim, Eugene, Dave, Simon, Vlad, and Lubomir

Production

- Dave: working on 10 new cathodes to be used in the first package, not in the second package as we always stated before. Again the bottleneck is the card gluing, but we will start making progress there, by tomorrow we plan to have the cathode strong-backs ready to be used to move the cathodes. Will start working soon on the other two cathodes that are needed to finish the first package. After that we will have two sets of cathode foils left.

- The third package is ready with the subsystems: grounding, cooling tubes, HV cabling. The plan is to move it to 126 tomorrow. The grounding worked fine, Vlad put ~100 clips for grounding as planned and another ~100 attached close to both sides of the cards (where possible and needed) to prevent the cathode deformation at the periphery. As Casey suggested, we used a new method to install the cooling tubes. We tightened the bracket on one card in the middle of the tube and installed the rest of the brackets loose. Then, going from the middle card toward the two ends of the tube we tightened the rest of the brackets. Thus, the copper tubes apply some pressure on the cards; before we had problems with some of the cards being pulled by the tubes. Gluing of the back brackets with green epoxy to the tubes was done at the end. In 126 after installing the cables we should experiment how easy will be to remove the extra clips we put on the card sides.

Cathode corrosion

- New SEM results from Olga (follow the above link) for the samples from the Vlad's test with the vacuum chamber; the chamber had water inside and the temperature at end of the day (lamps were off overnight) was close to 100degC. The test was done for about 4 days:

  • Copper foil with EPDM inside: significant corrosion, a lot of sulfur present.
  • With the EPDM of the gasket, part of the foil strips were inside the gas chamber and part exposed to the air: no sulfur seen at the air side and a lot of it at the gas side. However, inside the gas volume there was moisture and the temperature was much higher than outside. We had seen corrosion before also in the samples placed in air with some water put on the foils and no heating. We will do more tests.
  • Copper foil with Viton: some traces visible, almost no sulfur there but some chlorine. Tim suggested cleaning the O-rings before installation.
  • With Viton and Apiezon: no visible corrosion, only copper and carbon lines are visible, but the grease was not cleaned. Olga will repeat the measurements after cleaning it.

- The first testing chamber with production wire frame and cathodes was opened yesterday, exactly 4 weeks operating with HV and gas. Some traces from the EPDM O-ring are visible but it doesn't look like the corrosion on the first and second packages. We conclude that the humidity is an important factor. No traces on the cathode against the Viton+Apiezon O-ring are visible. The test with the small-scale prototype is running two weeks, haven't opened it yet.

- Tim for the humidity conditions in the Hall: nominally it will be less than 45%, but he can't exclude some periods when it might be higher. There will be dry air blowing through the magnet. We should avoid opening the Hall doors for a long time during the installation.

Engineering

- We will have two strong-backs to be used to grab the cathodes from both sides and keep them flat. We discussed how to support the cathode periphery when using the strong-backs. Casey made a table with rods that will be used to store the cathodes in a flat position.

- The rings for the cathode strong-backs came from the REX company right after the meeting, but there were issues with the fittings for the suction cups; also the weight of the aluminum ring seams too big.

Electronics

- Fernando: wrong zip file was send to the company for the PCBs; now all the files have the correct names to exclude such a problem.

- Main discussion was what to do the with these four PCB sets. Mechanically, compared to the original PCBs, there is a small difference in the gas connector positions (about a mm); according to Tim it will work and mechanically the wire planes will be interchangeable. Fernando: some of the signal traces are at different positions and the gold-plated ground area is bigger; the traces going through that area have to be covered with conformal coating. There should be no differences in the HV PCBs, but Fernando will check all the boards and on Monday we will decide if these can be used. Eugene: if you spend more than two weeks on these boards we better purchase new ones, which however will be tricky (at the end of the fiscal year) and will delay the production. Lubomir and Dave: we will need the boards in two weeks, if not we have to re-work the schedule.

TDR

- Lubomir received corrections from Bill and Simon, still some work remains to be done here.

Other

- Eugene urges us to do all the purchases for the FDC as soon as possible at least by the beginning of September; after that most likely there will be no money till the end of FY12.

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