September 8, 2011 FDC meeting
- Production Construction Tracking (Dave)
- Additional testing procedures
- First package tests (Lubomir)
- Engineering update (Bill)
- Electronics update (Chris)
- New testing card
- Chamber testing at EEL126 (Beni)
Participants: Bill, Dave, Simon, Beni, Elton, Mark, and Lubomir.
- Dave: The capacitors were changed on all wire frames needed for the first production package. Wires frame #6 was populated, wires deadened and will be put in package today or tomorrow. Wire frame #7 is out of the stringing table and Chris will put the elements on it tomorrow. The last two cathodes for the first package: started putting the rigid-flexes on type-1; on type-2 the frame was glued and on Monday the Mylar foil will be glued.
- After testing the first cell of the production package we found the following problems:
- One wire was broken at the standard place, between the pad and the epoxy. Casey fixed it already. Beni asked if this is a "standard place", how we can mitigate the problem. Dave: before soldering we started putting additional epoxy at that place that reduced the number of broken wires, so after that this is the first wire that we found broken. Beni and Bill discussed if this was caused by a frame deformation.
- One cathode channel didn't have a good contact; it passed the test with the diode testing card, but when we checked it with a generator the signals were attenuated. Re-heating the conductive tape for 30 sec solved the problem. However, after finding this we checked all the channels with a generator and found another bad channel. In this case re-heating for 30 sec didn't help. Casey decided to try re-heating for 60 sec and this time it helped.
- On the two wire frames that will go in the first package we found several broken resistors, some at the signal and some at the HV side. These are 1MOhm current limiting resistors. Most likely they were broken during the ring lamination when putting lead bricks on the top to make the ring flat. We were using cork pads bellow them, but Bill suggested another (polyethylene based) material. Also for the future we should avoid putting the bricks on the elements.
- All the above findings suggested that we need to do more tests before stringing and before stacking the wire frames and the cathodes:
- testing the resistors on the wire frames (with an ohmmeter) before stringing.
- testing the wire channels by applying step function with a generator on the +HV and looking with a scope at the individual channels at the connector
- testing of the cathode channels can be done with a generator (suggested by Anatoly) but it will require applying the signal on the other side of the strip which is not possible for the short strips in the middle. Another way is to induce the signals on all the strips by laying a cable from the generator on the top of the cathode. This method was used now to check all the cathodes for the stack. Probably the easiest way to do it is just to measure the resistance of the contacts.
- The first cell (with wire frame #5) was operational for almost a week. It was conditioned in 24 hours up to +2200/-500V (~500 nA total) and never tripped. On this wire frame the capacitors were not changed but covered with Humi-seal. The question is whether we want to change the capacitors on such wire frames that are working fine. Bill: we want to change them because the solder balls could move and cause problems in the future. The problem is that there's high probability one can damage the wires especially on boards with Humi-seal on the capacitors. We should try it on an old frames (or the first cell) before making decisions. Also on four of these frames we used Epon epoxy which may turn out to be unacceptable in any case, and that we can't replace.
- Beni and Elton stated that the priority now should be building the first package and later to decide about the capacitors. Beni also insisted we should move the second cell back to Blue Crab asap in order to understand the short between field and sense wires.
- The modified fixture for the wire deadening will come on Monday. Other parts/tooling for the package assembly will come next week, as well.
- Information from Chris before the meeting: all rigid-flexes were tested and found 5 (out ~500) that can't be easily fixed and will be shipped back for repair. In any case we have enough for the production.
- As discussed for the tests above we need to look at the wire and strip signals (or measure resistance) at the daughter card connectors. For that we need a card similar to the cathode testing card, same connectors on both sides but just with straight through traces to bring the signals outside of the frame. Chris will make such cards.
Chamber testing at 126
- Beni: done with the tests of cell #2. We should start preparing for the first package tests. Need to reorganize that space in 126, most importantly to find better place for the electronic racks. It will require re-cabling and again fight with the noise but has to be done. Valdimir will help.