Bond with current pulses

1
Wire-bond failures induced by resonant
vibrations in the CDF silicon detector

• Long after the end of commissioning a non
  negligible rate of permanent failures started to
  show up. Both failure modes are consistent with
  loosing the continuity on power lines on the
  non-accessible part of the detector.
• DVDD JUMPER connection
• Loss of the Z side information
• Wire bonds lying on a plane that is orthogonal to
  the magnetic field
• DOIM power connection
• Loss of all information from the module
• Wire bonds lying on a plane that contains the B
  Field vector but have a step up from a substrate
  to the other
• These are not the wire-bonds with the largest
  current in the system!
• Current surges (fusing the bond) were ruled out
• Aging mechanisms were ruled out

Time line of the silicon integration in CDF for
RunII
JUMPER route control, power and data between rF
and rZ sides of the double sided SVXII modules.
DOIM are laser diodes packages that drive data
from the tracking volume to the VME crates.
A perfect Wire-bond While resonated a crack grows at the heel The bond breaks on a time scale of minutes
Wire-bonds break due to fatigue stress on their
heel induced by resonant vibration. These
resonant vibrations are a direct consequence of
the oscillating Lorentz forces induced by the
magnetic field on wire-bonds with non-DC current.
A closer look with 40500 frames/second video
equipment
Resonant frequencies

• Single frames have been digitized and a
  quantitative analysis has been performed.
• Bonds were excited with limited number of pulses
  to measure the amplitude of the motion versus the
  number of pulses and the dumping ratio.

2-3 natural resonant frequencies up to 50 kHz
(range of interest for CDF) for realistically
shaped bonds. Each resonant frequency f can be
excited with pulses at f, f/2, f/4 etc
Bond with current pulses
Free decay of the motion

• The resonant system has a very high Q.
• The width of the resonance is about 1-200 Hz.
• Differently shaped bonds imply different resonant
  frequencies.

Bond without current pulses
40 pulses in a row
Conclusions
CDF operational response

• AVOID trigger conditions that could resonate the
  bonds.
• Administrative and Run-Control software.
• Understood and removed all possible spurious
  sources of the 5th L1A
• TS (Trigger Supervisor) firmware and Command
  Signal strength changes
• Current swing minimization
• Reduce the power
• output of the
• bus drivers
• Minimization of
• noise occupancy
• Trigger Inhibit on resonance (in place and being
  commissioned)

• Last fall the CDF experiment faced a crisis due
  to internal unrecoverable failures on the silicon
  detector.
• The source of the failures has been understood to
  be simple physics mechanisms that could have been
  taken into account during the design and
  construction of the hardware.
• Counter measures have been studied, developed and
  applied to the CDF experiment. Since these
  implementations are in place, no other failures
  have occurred.

Not real encapsulant
Small drops of encapsulant (Sylgard 186 Silicone
Elastomer from Dowcorning) limit the oscillation
amplitude by more than a factor of 50 by covering
just the first 50-100 mm of the wire. We were
not able to break these wire-bonds!
Gino Bolla, Purdue University for the CDF RUN2
Silicon Group
9th Pisa Meeting, La Biodola, Elba Italy, May
25-31