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Re: CDC Electronics Assembly



Hi Fernando,

Thanks a lot for the drawings. Some questions:

What is meant by the Conformal Seal? Does it refer to make the connector 
gas tight with glue? The problem with those new connectors is that the 
space between solder leads and connector are larger compared to the 
previous (smaller) one which makes that much more difficult. We even do 
not know yet if it is possible with the smaller connectors.

Going back to the PCB-feedthrough design. The argument was that when you 
solder the wires (coming from the straws) to it, they would make a 90 
degree angle with that PCB. Could we not make solder pads on that PCB 
(like you have for SM components) so that the wires can be 
soldered at 0 degrees. Those PCBs with wires can be prepared before 
detector assembly and we can use the new connector on the other side of 
that PCB.

Cheers,
 	Yves



                           /--------------------------------
                          /   Yves Van Haarlem
        _--~~--_         /
      /~/_|  |_\~\      /      Carnegie Mellon University
     |____________|    /        Department of Physics
     |[][][][][][]|:= /          Wean Hall room 8404
   __| __         |__ \       	 Pittsburgh, PA 15213
  |  ||. |   ==   |  | \           USA
(|  ||__|   ==   |  |) \
  |  |[] []  ==   |  |   \   	    Tel.:   +1 412 268-6949
  |  |____________|  |    \                  +1 412 641-9252
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On Tue, 12 Aug 2008, Fernando J. Barbosa wrote:

> Hello everyone,
>
> Following discussions with Yves and Slava, I have attached two pdf drawings 
> describing the assembly process. Note that these drawings are not to scale.
>
> Please provide feedback. Board design will proceed with the new EDAC 
> connector.
>
> Regards,
> Fernando
>
>
>
>
>
> Fernando J. Barbosa wrote:
>> Hello everyone,
>> 
>> I have attached a pdf describing the edge card connector from EDAC. This is 
>> similar to the one Gerard suggested but in 0.156" contact spacing. The 
>> connector part number is 307-030-500-202, which is a 30 contacts on dual 
>> row with a HV rating of 1800 V AC rms,  Thermoplastic Polyester insulator 
>> and $3.05. I searched for similar connectors and Sullins also has a similar 
>> one rated at 1800 V DC but with a different insulator (PPS Ryton). However, 
>> the cost for the Sullins part is five times higher at ~$15. The EDAC 
>> connector is stocked at Newark.
>> 
>> Now for the assembly details which are based on Slava's drawings. Slava, I 
>> would appreciate if you could email your drawings to those on this 
>> distribution list.
>> 
>> The assembly attempts to minimize the cable length from the straw to the 
>> connector:
>> 
>> 1. 24 RG-174 cables are prepared as follows:
>> a. Strip both ends so that there is the center conductor for soldering, 
>> insulation of center conductor, braid and outer insulation. Each is about 
>> .125 long so there are steps (different diameters).
>> b. On the straw side, prepare as is now planned with solder ball and 
>> conductive rubber. Maybe a heat shrink piece could be applied to secure the 
>> conductive rubber cylinder and cover the shield in one step.
>> c. On the connector side, slide each of the 24 cables into a small copper 
>> plate (perhaps a bit less than .125 thick) with 24 holes and solder the 
>> shield braids at the exit of the holes. The shields will all be connected 
>> together to the shield HV and to 2 connector pins. Solder each of the 24 
>> center conductors to the connector.
>> 
>> 2. The connector has 24 pins connected as in 1.c above, the next 2 adjacent 
>> pins connect to the copper plate to the shield HV, as in 1.c above. The 
>> next two pins are left unconnected and insulated or cut. the final 2 pins 
>> are soldered to a cable to attach to the endplate for grounding (ground on 
>> card is connected to endplate in this way.
>> 
>> 3. The back side (soldered connections) is sealed with the proper viscosity 
>> sealer and with low out-gassing characteristics (no silicone here). The 
>> finished part forms the connector assembly.
>> 
>> 4. Connect all the cables from all the cable assemblies to the straws and 
>> endplate (grounds).
>> 
>> 5. Attach dummy boards with straps to the edge card connectors on each of 
>> the cable assemblies.
>> 
>> 6. Position the gas plenum Plexiglass cover and feed all the straps through 
>> their respective holes on the Plexiglass cover. Slide this cover while 
>> pulling or straightening  the straps until the cover touches the 
>> connectors.  Attach the connectors with screws, washer and neoprene seal 
>> washer.
>> 
>> 7. Rotate CDC so that connector side is at top.
>> 
>> 8. Apply sealer (see 3 above) around each of the connectors/plexiglass 
>> holes.
>> 
>> In this way, we only need a short distance between the straws and the gas 
>> plenum cover. This is not very elaborate but  I can provide a drawing if 
>> necessary to better explain this technique. Please note that if one of the 
>> wires in the straws brakes and shorts tripping the HV, all the 24 channels 
>> in the group will be off. This is required because the shields are also at 
>> HV and the RG-174 is not rated for this level of HV. So, this is inherently 
>> safe.
>> 
>> There will also be an aluminum plate or aluminized mylar cover over the 
>> whole gas plenum and grounded for shielding.
>> 
>> Please provide feedback so we can finish the design of the HVB PCB. The HVB 
>> PCB will have the HV distribution network, the connections to the preamp 
>> card connector, grounding, etc. The preamp card, as in the FDC, is 
>> removable from the HVB.
>> 
>> Regards,
>> Fernando
>