Re: CDC Electronics Assembly

["Fernando J. Barbosa" <barbosa@jlab.org>]

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
>>
begin:vcard
fn:Fernando J. Barbosa
n:Barbosa;Fernando J.
org:Jefferson Lab
adr:Suite #10, 12B3;;12000 Jefferson Ave.;Newport News;VA;23606;USA
tel;work:757-269-7433
version:2.1
end:vcard