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Re: CDC Electronics Assembly
Hi Fernando,
I see, this brings me to the RG-174 cable - so we plan to put the shield
to ground and the signal part to 1800V - the cable is not being spect to
do that, right. Now we leave the shielding to float, before we put it to
1800~V as well.
If in the final design we leave the ground of the cables floating then we
do not have a problem with the PCB feedthru. If we plan to connect also
the cable grounds I believe we can make enough real estate on that
feed-through pcb to solder the signal part on one side and the cable
grounds on the other side of that pcb and have one more solder pad for the
grounding to the endplate. Asuming that the feedthru pcb is as broad as
the new EDAC connector is long. The old EDAC connector is half as long
and has 13 solder leads per side, that times 2 gives us 26 solder leads
on both sides of the feed through 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
/__\ /__\ \ Fax.: +1 412 681-0648
~~ ~~ \-----------------------------------
On Wed, 13 Aug 2008, Fernando J. Barbosa wrote:
> Hi Yves,
>
>
> Yves Van Haarlem wrote:
>> 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.
> There are adhesives with different viscosities for this purpose but we need
> to try them. I will test with the connectors you are sending me. The choice
> of the adhesive is very important in terms of its chemistry so that we don't
> end up with polymerization (aging) inside the straws.
>>
>> 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.
> Yes, this is a possibility. The issue with this approach is that we need to
> solder all over the shield (300 degrees?), not just at the shield/PCB
> interface. If we don't, the wires on the shield will be all over the place.
> However, we could just solder at the shield/PCB interface and then use a
> conformal coat of adhesive. We need to check this. Maybe two small PCBs, one
> for each row on a connector?
>
> Regards,
> Fernando
>
>>
>> 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
>> /__\ /__\ \ Fax.: +1 412 681-0648
>> ~~ ~~ \-----------------------------------
>>
>> 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
>>>
>