Latest FDC prototype design

["Daniel S. Carman" <carman@jlab.org>]

Hall D folks,

I have gone over the drawings provided to me by Randy Wojcik
and have a number of comments and questions.  I think in order
to complete the review/design process in the most timely manner
that we organize a telephone conference call.  This will save 
some of the back and forth and allow for us to converge more
quickly.  Elton Smith is gone this week to New York for the 
Intersections conference.  We should then aim to have our phone 
meeting next week.

However, I thought that it would be a good idea to circulate
the latest drawings that I have along with my questions so
folks can think about them in advance.

1). Figure: randyV3.pdf  (wire frame)

   - We need provisions for HV connectors on the PC board.  These
     should be PC Board mounted connectors.  Also, what are the
     holes in the PC board near the HV ``ears".
   - The definition of the ground planes remains a confusion for me.
     I think this is a matter of design style.  In the past I have
     had the highest noise immunity when I surround the signal
     traces with a sizeable ground plane.  In this design the signal
     traces are ``out in the open".  The ground plane is defined, as
     I understand it, on the opposite side of the board.  I would
     like to talk about this.  Noise immunity is an important
     consideration for this prototype so that we can make the
     most informed decisions on the electrode layout.
   - Will the PCB manufacturer drill the through holes on the board?
     If so, how are the dowel pin holes specified?
   - The width of the solder pads seems to be too narrow.  I prefer to
     have them 1.5 to 2.0 mm wide.
   - Will there by a solder mask included?  
   - The signal traces running from the solder pads to the connector
     have sharp corners.  Is this just an artifact of the drawing
     program?  I prefer smooth curves to reduce the possibility of HV 
     breakdown and signal reflection.
   - What is the difference between the blue HV bus and the red HV
     bus?  Are they meant to be on opposite sides of the board?
   - Need to include external sighting mark to locate chamber relative
     to an external reference.

2). Figure: cathodeV3.pdf  (cathode board)

   - The cathode board design has me confused still.  When last we
     talked, we decided to make the cathode plane (the copper-cladded
     kapton) larger in size so that we could include dowel pin holes
     to improve the alignment and positioning.  But I assume that we
     are still mounting it on top of a G10 frame.  How then will we
     make provisions to connect this to Fernando's signal readout
     board?  How is the kapton attached to the G10 frame?
   - What about holes for gas flow through the kapton?
   - Why are the cathode strips uneven at the ends?
   - Is there going to be any ground plane definitions on the cathode
     board?

Also, we need a full mechanical drawing for the final design.  For
example we need to ensure that the clearance of the G10 spacer above 
the solder pads is proper.  Also it is not clear to me how many G10
spacers are included.  We had discussed at one point that maybe we
could reduce the number of these spacers by two.  Finally we need to 
see the design for the aluminium frames to double check the location
of the O-ring positions and the gas input and output attachments.

In the mean time, please let me know if there are any design decisions
still in the open that need to be thought about this week.


					Daniel

**********************************************************************
*                                                                    *
* Dr. Daniel S. Carman                   e-mail : carman@jlab.org    *
* Ohio University                        office : (740)-593-2964     *
* Department of Physics                  fax    : (740)-593-1436     *
*                                                                    *
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