note from meeting with sidet this morning

[David Winter <winter@nevis.columbia.edu>]

hi all,

several of us (dave, me, RJ) met with bert and hogan today to discuss 
their observations about the fixtures that have been fabricated.   i'll 
start with what i see as the action items that came out from the discussion:

- RJ will send to sidet the offsets that would be required to create 
shims for the main assembly fixture, to allow the backplane to be 
positioned without pedestals attached to it (needed for them to use 
current parts with the fixtures)

- RJ will also report how difficult it would be to design & fab chip 
positioning fixture with "walls" between the chip areas, allowing the 
chips to be efficiently placed

- Bert is going to explore a tweak to the chip positioning fixture where 
he's added 160 micron wires to act as the "walls" mentioned in the 
previous bullet.

Here's a more detailed summary of the discussions.

- one issue that Bert has raised is how challenging it will be to 
position the chips using the current fixture: one edge (along the long 
side of the chips) and scribe lines to space the chips (200 um between 
them).  we talked about the possibility of adding another edge instead 
of scribe lines.  RJ is going to look into the difficulty of doing so.  
It may be that extra expense may be offset by increased efficiency and 
reliability in the assembly.  Bert has also come up with a tweak whereby 
he uses 160 micron wires to act as stops at the position of the scribe 
lines; this could allow them to operate efficiently with these fixtures.

- the current fixtures were designed under the assumption that 
backplanes would be delivered with pedestals already attached.  this 
poses a problem for bert since there are no such parts available.  we 
discussed various scenerios.  the first would be for sidet to produce 
shims that would allow roughly correct placement of the backplane in the 
recessed cutout of the main assembly fixture.  the next would be a new 
fixture in the same spirit as the sensor positioning fixture, with dowel 
pins placed appropriately for the dimensions of the backplane.  if the 
backplanes are delivered with pedestals, the current fixtures are 
appropriate.  should we need the pedestals placed on after the assembly, 
we will have evaluated some of the issues of assembling with 
pedestal-less backplanes.

- It also turns out that the process of laying down a thin strip of 
arclad is extremely time-consuming.  in the current model, there would 
be effectively two such strips laid down per side (one for chips, then 
later another one for the sensor).  we discussed the possibility of 
placing the chips and sensor at the same time.  this would greatly 
improve the ability to lay down arclad -- a single large, template piece 
could be cut to size and easily placed.  The consequence would be that 
should we have to test for bad chips before wirebonding the sensors, and 
a procedure would need to be developed to replace single chips.  we'll 
have to think about it.

dave

--
David L. Winter, PhD
Columbia University in the City of New York
Nevis Laboratories
winter<AT>alum<DOT>mit<DOT>edu
http://www.nevis.columbia.edu/~winter
212-854-5680 (Campus Office)
914-591-2819 (Nevis Office)
631-344-7843 (BNL Office)

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