BVDC Bias Voltage Distribution Card ---------------------------------------- Original Rev. 2-July-2007 Current Rev. 10-Oct-2007 This file describes the layout details of the 24 channel Bias Voltage Distribution Card, i.e. the BVDC-24. The BVDC card is 4.200" in the "X" axis, i.e. along the Wire Frame and it is 5.000" in the "Y" axis, i.e. perpendicular to the Wire Frame. The BVDC-24 card uses 7 component types. They are: R1:R24 100 Meg Ohm Resistor R25 2 Meg Ohm Resistor R26, R27 100 Ohm Resistor C1:C30 10 nFd 1600 Volt capacitor J1 50 pin double row 0.1" x 0.1" 25 mil sq pin header for the readout cable J2, J3 12 pin receptacle that plugs onto the Wire Frame J4, J5 3 pin Raw Bias Voltage Connectors pins are spaced 0.2" 25 mil sq pins 90 deg bend All component types have been selected to reduce the risk of contamination of the LAr. The circuit board itself for the BVDC will be made from G-10 rather than from the more conventional FR-4. A completed BVDC will be tested in the PAB Materials Test System before the BVDC cards are assembled in the T962 cryostat. Quantity of BVDC Cards to Manufacture ------------------------------------- We need to make enough BVDC-24 cards for either: 480 wires --> 20 BVDC cards --> build 25 cards 720 wires --> 30 BVDC cards --> build 35 cards 25 x 24 = 600 35 x 24 = 840 the delta is 240 components Parts List ---------- 100 Meg Ohm Resistor Ohmite Slim-Mox 102 Digikey Part No. SM102F-100M-ND $1.37 ea in quantity of 200 Order Quantity: 850 2 Meg Ohm Resistor Ohmite Slim-Mox 104 Digikey Part No. SM104F-2M-ND $2.77 ea in quantity of 100 Order Quantity: 100 100 Ohm Resistor Dale RN55D CMF resistor Newark Stock No. 83F1313 $0.12 each in quantity of 100 Order Quantity: 100 0.01 uFd 1600 Volt ICC PPB Capacitor Newark Stock No. 30K6562 Polypropylene Film $0.58 ea in quantity of 250+ Order Quantity: 850 12 position receptacle AMP 1-535676-1 for 25 mil sq pins Digikey Part No. A26412-ND spaced 0.1" Rt/Angle $2.25 ea in quantity of 25 Order Quantity: 40 Bias Voltage Connector Molex Header 36 pin right angle each 36 pin stick Molex Part No. 22-28-8362 makes 6 connectors Newark Stock No. 56H3123 need 70 connectors $1.60 ea in quantity 10-24 Order Quantity: 20 Readout Connector 3M Part Number 2550-6002UB 50 pin 2 row header Newark Stock No. 46F4733 0.1" x 0.1" 25 mil $1.93 ea in quantity of 25+ straight solder tails Order Quantity: 40 PCB Layout Details ------------------ The BVDC card was layed out with all of the signal traces on the top side and the bulk of the bottom side is a Ground plane. There are no vias carrying signals on the BVDC card, i.e. it can not have a broken via problem when it gets cold. Design rules were used so that a minimum relief of 3mm exists between signal traces at the Bias Voltage and the Ground plane. Wherever possible space was used to hold a much wider relief between the Bias Voltage elevated signals and the Ground Plane. At its tightest the signals were run on 20 mil traces with 25 mil space between the traces. 12 mil traces were used only to escape the 50 pin connector header. The end of the BVDC card that is away from the Wire Frame has two holes to hold a pair of 6-32 nylon jack screws. The intent is that these jack screws could be used to support the far end of the card. If a strip of G-10 is put along the top edge of the HV Cage then these jack screws could also be used to guarantee that the BVDC cards do not unplug from the Wire Frame. The same thing could be done along the vertical edge mounted BVDC cards by taping holes in such a G-10 strip for the jack screws. These is also a hole for a 6-32 screw centered between the two connectors that plug into the Wire Frame. This is available for mounting purposes if it is useful. The foot print for the 12 pin connectors that mount to the Wire Frame includes extra holes so that this connector could be expanded to carry the BVDC Ground to the Wire Frame. A 15 pin connector could be used which would carry 2 Grounds along with the 12 wire signals. Note that one pin in this 15 pin connector is clipped out to give sufficient relief between the Bias Voltage elevated wire signals and Ground. The BVDC card has two connectors for the raw Bias Voltage so that the raw Bias Voltage can be daisy chained from one BVDC card to the next. Each of these connectors is a 3 pin connector with the pins spaced 0.2". In each connector: 2 of the pins are for a ground shield and 1 pin carries the Bias Voltage supply. The 2 ground shield pins in each connector are tied to the BVDC card's Ground Plane through 100 Ohm resistors to break the ground loops. The pin headers on the Wire Frames that plug into the 12 pin AMP 1-535676-1 connectors on the BVDC should have pins that are about 0.3" long. The raw Bias Voltage supply can plug onto the BVDC cards using: AMP 1-87309-4 crimp contacts (Newark Stock No. 90F3791) and AMP 87499-9 housings (Newark Stock No. 90F7738). Testing of the BVDC cards ------------------------- Clearly the BVDC cards must be carefully tested before they are assembled into the cryostat. - A simple test may be to use Neon bulbs (NE-2's with 100K Ohm resistors) and plug them into the Wire Frame connectors. Then apply 250 Volts or so the the Bias Voltage connection. If the Readout Connector signal pin is tied to GND then the corresponding bulb should flash at about 2 Hz. Open the Readout Connector signal pin and the bulb should stop flashing. This test would check all of the parts, and check for leakage, and check for opens or shorts. - A more conventional test would be to use a high input impedance meter (like the Dana 5900) and check the Wire Frame connectors with a few hundred Volts of Bias Voltage plugged into the card. Check with the Readout Connector open and shorted to GND. Still need to check the signal output path. Question: How to safely discharge all of the 0.01 uFd capacitors after this test ? Do NOT want to spark them as that is a good way to create noise or leakage problems. Short the Bias Voltage connector and short the Readout connector and let them discharge through the 100 Meg Ohm resistors. Cleaning of the BVDC cards -------------------------- Clearly the BVDC cards must be carefully cleaned before they are assembled into the cryostat. The default process would be: Ethanol then Alconox soap then water then distilled water then cook dry at 50c in Ron's oven. Package in Zip-Lock bags.