Minutes-10-20-2011

October 20, 2011 FDC meeting

Agenda

1. Production Construction Tracking
   • Status (Dave)
   • First package tests (Lubomir)
   • Resistance of z-axis conductive tape (Lubomir)
2. Engineering (Bill)
   • Cooling/grounding system
   • Other: protective covers, new hubs, ...
3. Electronics update (Chris)
4. Testing set-up at EEL126 (Beni)
5. Other

Minutes

Participants: Eugene, Bill, Tim, Beni, Mark, Vladimir, Chris, Dave, Glen, Simon, Casey, and Lubomir.

Production

- Dave: Working on second package. First end window ready, second will be ready by the end of the day. Two cathodes (type-1) are ready. Another two cathodes (type-2 and 3) just need the daughter cards to be put on (the last operation). The first wire frame was strung and taped, but there were some delays with the position measurements. Wire scanning stops in the middle of the chamber, most likely due to a combination of software and hardware issues. Will try to find the Caleb's original software (Parker ACR project) and use it, at the same time to identify why it stops, which is the signal causing this.

- Lubomir: Vladimir tested all the channels from cell#4 top cathode to the top of the package. All channels are working. The exception is a noise seen on two channels, one on the bottom cathode and one on the top cathode of cell#6. Some smaller noise is seen also on their neighbors, mots likely induced from them. The noise looks like discharge, a sharp random signals (~10-20ns from the pre-amp) with amplitudes ~100-200mV and frequency ~1kHz depending on the HV. Vladimir checked carefully but couldn't find similar noise on any wire. The top and bottom strip showing noise do not cross each other. The noise appears only if there's HV on sector #4 for the top strip and on sector #2 for the bottom strip. In both cases the beginning of the strips and their traces leading to the connector are very close to the HV distribution chain on the PCBs for the corresponding sector.

- To investigate the noise problem, cell#6 was disassembled. Using a new card (made by Anatoly) now we can measure the resistance between the strip and the corresponding pin on the daughter card. We found that these noisy strips have higher resistance than normal: ~10 Ohms, compared to 1.5~4 Ohms. It was found also that bending the cathode frame may increase the resistance, after some relaxation in may come back, but also may stay higher and eventually can be "fixed" by bending the frame again. Similar problem was found on other channels of these two cathodes. Re-clamping/re-heating the conductive tape solved the problem in all the cases except one, the connector on the bottom cathode that has noisy channel. There Casey had to replace the daughter card. After removing the old card we looked with a microscope: the silver balls from the conductive tape were visible on all the connectors, the conductive tape glue was much ticker between the pads than below the pads (due to the holes between the pads on the flex), no dents on the cathode side, but some silver balls were embedded in the tinned pads on the flex. We discussed possible reasons for enhanced resistivity and decided to do more prototyping with the z-axis conductive tape. Eugene pointed that 10 Ohms is too small to cause noise problems. The strip capacitance was measured after the meeting on a separate cathode (it is very difficult to measure it inside the package since the card used to connect to the strips has much higher capacitance): ~10-20 pF between strips, ~40pF between strips and ground plane. Since in the package we have another ground plane further away one can assume the strip to ground capacitance is <100pF which at 10 Ohms gives a time constant of <1ns to be compared to the 10ns of the pre-amp.