Revision as of 14:49, 17 August 2012

August 16, 2012 FDC meeting

Agenda

1. Cathode production Construction Tracking (Dave)
2. Cathode corrosion
   • Status [1]
   • Possible procedure changes
3. Conductive tape technology
   • Test results [2], ball counting hist.#1, ball counting hist.#2, ball counting hist.#3, big ball distribution, small balls distribution, big+small balls distribution
   • Procedure changes
4. Engineering (Bill)
   • Cathode strong-back
   • Other: epoxy tests
5. Electronics (Chris, Nick)
   • PCBs
6. TDR, pages 132-145 (Lubomir)
7. Other

Minutes

Participants: Eugene, Bill, Dave, Simon, Vlad, Beni, and Lubomir

Cathode production

- Dave: working on 8 new cathodes to be used in the second package. The bottleneck is the card gluing since we have not decided if we want to change the procedures.

Cathode corrosion

- Lubomir about the SEM results: On the wire samples some small crystals (~3um) are seen containing sulfur, Olga counted about 25 of these on 2cm wire length; too small quantity to account for the copper damage on the cathodes. On the EPDM surface - no conductivity and very low yield from the microscope - still one sees some sulfur on the used EPDM, but much less or nothing on the virgin EPDM and on the prototype EPDM. Dave will check if the virgin and used EPDMs are from the same batch.

- 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 before continuing with this procedure.

Conductive tape technology

- 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.

- 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 that there's conductivity. 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

Engineering