[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: CDC Electronics Assembly
Hi Fernando,
Thanks for the drawing. I was actually thinking of sealing the pcb in the
endplate which would be much easier to seal than the connector.
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,
>
> The shield is at HV (1800 V) and the inner conductors are at the same HV but
> with the series resistors; the signals are decoupled from the inner
> conductors with HV caps to the preamps. In the drawing, pins 13 and A13 are
> labeled HVshield. So, the potential between the shield and the inner
> conductor is about zero.
>
> I attaching the new PCB option with the updated drawing. It seems we have
> email problems.
>
> Regards,
> Fernando
>
> Yves Van Haarlem wrote:
>> 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
>>>>>
>>>
>