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

[Fernando J. Barbosa]

Hi Gerard and Tim,

    I suggest avoiding any plating using nickel on aluminum. Although 
there are some newer processes such as electroless nickel, blisters and 
de-lamination often occur. We had this problem at BNL with a standard 
industrial process on aluminum endplates for the EVA straw chambers 
(this occurred after 6 months in a non-controlled environment).

    Chromate conversion coatings should work well but the thickness of 
this coating is critical. Please check MIL-C-5541, Class 3 for this 
application. The thickness of this coating will need to be considered 
for the machining tolerances on the endplate.

    Considering the no-plating option, the metal insert that locates the 
straw and makes the connection from the straw donut to the endplate with 
conductive epoxy should be reliable if the endplate is clean and if the 
assembly is performed in a dry environment. For additional protection of 
these joints, Humiseal 1B31 or 1B73 can be applied over the conductive 
epoxy joint. For the case of the ground connections with the threaded 
socket or bolts, you could use a copper or silver loaded lubricant/paste 
designed to prevent corrosion at the interfaces.

Best regards,
Fernando



Gerard Visser wrote:
> Hi Tim,
>     Well, anything that is reliably conductive on contact.
>     I guess the best is gold (over a nickel flash of course).
>     However any of the conductive "chromate conversion" finishes 
> should work fine. This is widely used for aluminum parts in electronic 
> equipment. I don't have much experience with specifying plating, I did 
> know something a long time ago but would hesitate to try to recall it. 
> But I think this chromate conversion finish is covered in one of the 
> mil standards and that is probably the place to look for how to 
> specify it.
>
>     - Gerard
>
> Tim Whitlatch wrote:
>> Hi Gerard,
>>
>> What type of plating did you have in mind?
>>
>> Gerard Visser wrote:
>>> Hi Tim,
>>>     Is it possible to find 152 appropriate locations for this 
>>> 4947-0-15-15-34-27-40-0 pin socket? [With clearance to allow a 
>>> nutdriver to install it - maybe that is not an issue at all because 
>>> of the height of this part but I'm not familiar enough with the 
>>> design at this point to know.]
>>>     If you think you can fit them in, yes I at least would advocate 
>>> that you do so and have the vendor do the work as the baseline plan. 
>>> Seems to me much easier than to rework the part later. These holes 
>>> will not need to be very precisely located but it still must amount 
>>> to a significant amount of setup work considering the size and 
>>> complexity of the endplates.
>>>     Of course, this requires a decision from others, it is not my 
>>> place to ask you for this. I understand (correctly?) you will be 
>>> having a phone meeting with CMU tomorrow anyway, I can join this 
>>> briefly if you want to add this topic to the agenda. Please let me 
>>> know.
>>>
>>>     - Gerard
>>>
>>> p.s. Is the endplate going to be plated? Bare aluminum of course may 
>>> have issues with adequate contact in the presence of oxidation. (Not 
>>> just for these ground pins but also for the straw attachment and 
>>> others. Plating is not that expensive in comparison to the 
>>> enhancement of reliability of the connections.)
>
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