Loop doc for Sen-Sen bonds from Fermilab

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Loop doc for Sen-Sen bondsfrom Fermilab

• Lenny Spiegel
• Jan 30th, 2006

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FNAL Sen-Sen bonds
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FNAL Sen-Sen bonds

• When the issue of sparking arose, in November
  2005, we changed our TOB sensor-sensor signal
  bond profile to increase the height of outer
  sensor bonds above the n implant. At the same
  time we eliminated 2 out of 6 sensor-sensor bias
  bonds, which were at the same height as the
  signal bonds. Thus we have two profiles1.  A
  "square" profile for the first 76 of TOB modules
  constructed at FNAL.                   loop
  height                 505 microns              
       n critical clearance   140 microns outer
  sensor (sensor 2)2.  A "triange" profile for
  the last 24 of TOB modules.                  
  loop height                 513
  microns                   n critical
  clearance   286 microns outer sensor

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FNAL Sen-Sen bonds

• In both cases we are using the first set of bond
  pads on the sensors (unlike UCSB which switched
  to second set for their outer sensors when they
  changed profiles in November 2005). Also, in
  reporting the above numbers I have subtracted
  the 25.4 micron diameter of the bonds from the
  microscope focus measurements as this gives a
  better indication of the clearance distance.
  Finally, it should be understood that the above
  numbers are averages obtained from a limited
  sample of measurements and that there is a fair
  amount of variation, so that some n clearances
  are around 100 microns or less.I've enclosed a
  picture of the "square" profile don't have one
  of the "triangle" profile.We are starting a
  program in the US to encapsulate all
  sensor-sensor bonds (including the bias bonds)
  for ALL TOB (and TEC) modules assembled here. In
  theory the encapsulate material (Dow Corning
  Sylgard 186) gives a factor of 5-6 improvement on
  air - for large gaps (2cm). In practice we find
  it difficult to show that the encapsulant buys
  more than a few hundred volts in the maximum
  operating voltage. However, a few hundred volts
  is still significant and, in any event, we have
  started the process.