# Presentation: 083297

## G. BollaPurdue UniversityFor the CDF Silicon Task ForceMany thanks to:CDF collaboratorsSiDet (FNAL Silicon Detector facility) TD (FNAL Technical Division)

- Wire-bonds failures induced by resonant vibration in the CDF Silicon Detector

- G. Bolla, IEEE NSS 2003 Portland OR

## Outline (really a time-line)New Failure Mode well after commissioning 

- G. Bolla, IEEE NSS 2003 Portland OR

## First observations and immediate reaction

**The failures were tracked down to anomalous trigger conditions during data taking.**
**Trigger TORTURE tests (to explore dead-time at high trigger rates)**
**Fake triggers generated according to the fixed beam structure. ****Synchronous!.**
**High Dead time runs (due to problems in the experiment)**
**SVX3 chip can go in a HIGH occupancy (100%) mode if 5****th**** L1A is issued (buffer is only 4 deep)**
**Long readout time drives CDF into issuing a trigger as soon as there is a free buffer. This happens with a fixed time interval between each other. ****Synchronous!.**
**Failures concentrated on an integrated time of a few hours to be compared with ~ 2 Years of operations.**
**This must be something that we can avoid!**
**Introduction of a rate limit at L1 for the experiment**
_**Only reaction possible with the limited knowledge.**_
**Started the investigation**

- G. Bolla, IEEE NSS 2003 Portland OR

**Notes:**
Forget the comment on HIGHER luminosity

## Symptoms of the failures

**DOIM failures:**
_**No more data from the module.**_
**Only feedback is the current consumption on the power lines**
**Module still responds to all the detectable inputs.**
_**Sudden drop on the Port-Card current consumption**_
**Loss of 1/5 of the power consumption**
_**Occurred on both ISL and SVXII**_
**DVDD Jumper connection**
_**No more useful data from the Z side of the module**_
****** ****side still operable and symptoms free**
**Increase by 10-15 % of the Analog power consumption (AVDD) and consequent trips.**
**Extra AVDD current is strongly dependent on what the Digital part of the chip is doing**
_**Failures are confined to SVXII only**_
**Symptoms have been successfully reproduced on the bench (with spare modules) and are consistent with the loss of continuity on specific power line at well identified locations in the hardware**

- G. Bolla, IEEE NSS 2003 Portland OR

## What are the power lines that fails?

- DOIM TX Power
- (Dense Optical Interface Module Transmitter)
- Vertex 2002 presentation by S. Hou
-  8 bits + clock optical link that transmit the data from the tracker to the VME boards.
- Laser diodes are powered with a differential power supply:
- Granularity of the failure indicates wire-bonds breaking/fusing.
- Other single point failures are not consistent with the symptoms (very specific)

- SXV3 chip Digital power (DVDD)
- from  to Z side.

- Same connection as for everything else.
- All control signals
- All data lines
- Analog power as well
- 5 times higher current in steady state condition
- Never Less than 2 times higher

- G. Bolla, IEEE NSS 2003 Portland OR

## What do they look like

- G. Bolla, IEEE NSS 2003 Portland OR

## Multiple lines of investigations

**Power surges in time scales short enough not to trip the Power Supply and still capable to fuse the wirebonds.**
**Extensive measurements of the energy needed to blow the wirebonds**
**Extensive analysis of the energy stored locally in the detector**
**Extensive analysis/measurements of the time response of the tripping circuitry of the power supplies**
**This mechanism was ruled out. More than a factor of 5 safety margin**
**Aging of the various components in the power lines.**
**Focused on the ****vias**** on the small jumper**
**Accelerated aging tests (high Temperature & high current)**
**No failures up to *****20 years equivalent***** of data taking **
**(we stopped after ~4 weeks at 120 C with 1 A per VIA)**
**Power surges on the complex ground of the system.**
**Hard to replicate on the bench**
**A deep review of the GND connections. Nothing really came out of it.**
**Fatigue on the wire-bond heel induced by Lorentz Forces.**
**	****Similar work done in the past for completely different reasons (IEEE Transaction on Components, Hybrid and Manufacturing Technology, Vol 14, NO 4, December 1991)**

- G. Bolla, IEEE NSS 2003 Portland OR

**Notes:**
Go straight to the punch line that is point 4

## How is the current on those lines?

**Both have a behavior that is trigger dependent**
**DOIM:**
**The output of the current amplifier feeds either the laser Diodes (bit HIGH) or a dummy load (bit LOW)**
**The 2 loads are supposed to be perfectly matched.**
**Dynamic measurements have been performed on a sample of DOIM TX packages left over.**
**The ********I distribution is centered at 0 current with tails up to 20 mA.**
**DVDD Jumper connection**
**The digital part of the SVX3d (BE) chips have a current consumption that is strongly time dependent.**
******mA/chip while waiting for a trigger **
**Doubles up during digitization (we have an on chip Wilkinson ADC)**
**Grows up to 120 mA while reading out.**
**Capacitors on the lines smooth up the behavior**
**The time spent in the high current mode is occupancy dependent (on chip sparsification logic)**

- G. Bolla, IEEE NSS 2003 Portland OR

## Bonds and Lorentz forces

**With a 1.4 T Magnetic Field, 200 mA of current and a 2 millimeter bond in a plane that is orthogonal to the field the forces are in the range of 5E-4 N (50 mg). **
**The induced movement should not exceed 3-4 ********m (hard to measure on a 25 ********m Al wire)**
**Resonant behavior is expected and the natural resonant frequencies are in the KHZ range depending on the length and shape of the wires (CDF is interested only up to 50 KHz)**

- G. Bolla, IEEE NSS 2003 Portland OR

## Detection of the resonances

**With regular video equipment the resonances were detected.**
**The amplitude of the oscillations is consistent with a few wire diameters **
**Test wire-bonds while oscillating break in time scales of minutes.**
**At 10-20 KHz this implies ~ 10E6 - 10E7 cycles.**

- G. Bolla, IEEE NSS 2003 Portland OR

## What happens at the heel

- 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.

- G. Bolla, IEEE NSS 2003 Portland OR

## A closer look with 40K fps camera

**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.**
**3 pulses (at the right frequency) are enough to induce motion**

- G. Bolla, IEEE NSS 2003 Portland OR

## Very narrow resonances

**2 natural resonant frequencies up to 50 kHz (range of interest for CDF) for realistically shaped bonds.**
**With current pulses each resonant frequency f can be excited with pulses at f, f/2, f/4 etc **
**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.**

- G. Bolla, IEEE NSS 2003 Portland OR

## F.E.A.

**The system is very simple and can easily be simulated**
**The agreement with the experimental results is very good**

- G. Bolla, IEEE NSS 2003 Portland OR

## Operational response

_**AVOID**_** trigger conditions that could resonate the bonds.**
**Administrative and Run-Control software.**
_**Understood and removed**_** all possible spurious sources of the 5****th**** L1A**
**TS (Trigger Supervisor) firmware and Command Signal strength changes**
_**Current swing minimization**_
**Reduce the power output **
**	****of the bus drivers **
**	****(programmable)**
**Minimization of noise **
**	****occupancy**
_**Trigger Inhibit on potential resonances**_
**Count time between readout commands (********t****i****)**
**If (********t****i**** -********t****i+1****)<****1********sec**** C++**
**If C > ****5**** pull the brakes**

- G. Bolla, IEEE NSS 2003 Portland OR

## Possible solution (obvious)

**The small amount of encapsulant was placed by hand**
**By placing the encapsulant only at the foot the problematic associated with not perfectly matched CTEs should be minimized**
**No effort on our side toward any large scale technique (too late for CDF)**

**Small drops of encapsulant**** **
**(**Sylgard 186 Silicone Elastomer from Dowcorning) **limit the oscillation amplitude by more than a factor of 30 by covering just the first **
**50-100 ********m of the wire.**
**We were not able to break these wire-bonds!**

- G. Bolla, IEEE NSS 2003 Portland OR

**Notes:**
Add the picture of the foot

## Conclusions

**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.**
**Similar problems could be faced by other applications.**

- G. Bolla, IEEE NSS 2003 Portland OR