[Halld-tracking-hw] CDC feedthrus and end plate

[Gerard Visser]

Hi Fernando and Tim,
	Please consider as I mentioned the use of a pressfit pin socket in the 
endplate if space is at a premium. [Well, ok, I think we know that is 
true...] I don't know if this is really practical in aluminum, it 
certainly works in printed circuit boards. I think it would be 
relatively easy for you to make some tests, if you can afford to delay 
releasing the endplate drawings for a little while yet.
	Consultation with Mill-Max (or other vendor) might give a more accurate 
judgement of which socket to select and whether it will work. But 
naively I think - trying to stay small - that for instance Mill-Max # 
0252-0-15-15-32-27,
http://www.mill-max.com/pin_rec_catalog/productInfo.cfm?webpartnumber=0252&start=1&leaddiameterrange=.015-.025&pin_or_rec=&PartDescription=Receptacle%20With%20No%20Tail&taildiameter=NONE&tailtype=NONE&mountingfeature=PRESSFIT&mountinghole=0.057&bodylength=&search=&pr=Rec&stagecode=
  pressed into a (round) hole 0.057+/-0.002 x 0.150 min depth (not to 
break through, of course), and located anywhere that there is 0.080 
diameter clear area on the outside surface of the endplate, would do 
nicely. If you can find 152 such appropriate locations for this, one 
near each preamp connector. We can certainly find a ~0.020 diameter pin 
to crimp or solder on the ground wire, to plug into this socket.
	I just think that this might be easier to accomodate than tapped holes, 
and also easier to actually install the ground wires. Of course, a lug 
under a screw is probably a better connection, so if there is room for 
that I certainly don't want to dissuade you from that approach.
	Use of the pressfit pins should certainly be conditional on some tests 
to see how they go in bulk aluminum, which is not their usual 
application. And also probably to optimize the diameter. Also of course, 
this approach would add an additional setup and processing step to the 
endplate production, must cost a little.
	Please consider it, unless you have a reason to rule this out immediately.
	Sincerely,

		Gerard

ps. The ground wires can be solid bare wire (#16 - #22), no? That seems 
the easiest to me. [And actually #22 solid wire can be plugged right 
into this socket, assuming it is cleanly cut; if using tin-plated wire 
then the contact should be changed from gold to tin, also a standard 
option - but leave the body plating gold. Bare copper might be 
preferable though. Or a slightly larger pin for #18, e.g. 
0334-0-15-15-34-27-10-0. Maybe that is the way to go, looks even better.]

Fernando J. Barbosa wrote:
> Hi Gerard and Tim,
> 
>     I am in agreement with Gerard. I have always made the point that the 
> shorter the connection (any) the better and distributed throughout the 
> end-plate. Slava has also made the point that a direct connection (say, 
> a stud through the gas plenum) would be impossible due to the density of 
> the straws and the location of the preamp card connectors.
>     Ground wire (16 AWG w/FEP insulation?) connections in a regular 
> pattern will work better than the peripheral connection attachment. Of 
> course, the quantity of these connections will need to be determined but 
> I agree that we should make provisions for as many as possible even if 
> not used in the final configuration. I have not looked at the latest 
> drawings in detail but I requested a large number of blind taped holes 
> throughout the endplate when we were considering different alternatives 
> to the straw connections in the past - maybe these were dropped along 
> the way.
>     The grounded disk is supposed to be copper and there are no major 
> constraints on the thickness, other than cost. But this is already an 
> expensive disk due to all the machining that will be required.
>     Therefore, if there are no mechanical strength issues on the 
> endplate, let's add the taped holes throughout the endplate and make the 
> connections as Gerard suggests.
> 
> Best regards,
> Fernando
> 
> Gerard Visser wrote:
>> Hi Tim,
>>     Yes, I know. This (152 direct lines) is what I had in mind. Maybe 
>> it is too much to ask for. Your question whether we can live without 
>> it is a good one, wish that I (or Fernando) knew the answer 100% for 
>> sure. *Perhaps* the answer is yes. If I had to guess, I'd say better 
>> than even odds.
>>     One the other hand if you could for instance add the 152 features 
>> (4-40 blind taped hole? or a blind hole to fit a Mill-Max press-fit 
>> pin socket? or something like this?) to the endplate, then if the 
>> eventual answer turns out to be no, it does not mean the finished, and 
>> I imagine rather expensive, endplate is unusable.
>>     It was the absence of any such features as far as I could 
>> understand in your drawing, that stimulated this discussion.
>>     If it is simply impossible to have 152, or even 152/2 or 152/3 or 
>> 152/4 by some sharing scheme, then we must risk doing without it. If 
>> it is possible, my opinion is the features should be added, they can 
>> always be left unused if it turns out that we don't need them, i.e., 
>> if grounds around the outside will not suffice.
>>     By the way, the boards will (I really hope) be sitting on a ground 
>> plane, e.g., the upstream plenum is a sheet of thin aluminum, right? 
>> Because I can pretty much guarantee you that 152 preamp boards with 
>> each a skinny 40 cm ground wire between the preamp and the endplate, 
>> this will not work. If the connection is through a common sheet of 
>> (preferably plated) aluminum, it stands a good chance but I would 
>> still be nervous that the direct (152 5cm lines) plan might prove to 
>> be necessary.
>>     Well, I think we should consider this more and you'll have to tell 
>> what you can really do. But the shorter, wider, more distributed the 
>> ground connections are, the lower the risk and potentially the better 
>> the performance. We must not forget this :)
>>     Sincerely,
>>
>>         Gerard