1. Recent TOB Developments
C. Campagnari
On behalf of the US module testing groups

2. Outline Status Update CMN (Micro-discharge) Problem
4 Hybrid Thermal Cycler
Stereo and 6 chip module production
Dead pipeline column fault
Module Burn-in (Wien Cold Box) Status
Grounding improvements
Backplane pulsing
First US Rod
CMN (Micro-discharge) Problem
Description of problem
Why you should be concerned about it?
Studies performed
Future plans/Request for aid

3. Hybrid Thermal Cycler-Pulser
Now fully commissioned at UCSB
Many thanks to CERN group for their constant aid
~40 minutes to thermal cycle 4 hybrids
6 hybrids had APV-PA bonded at UCSB
4 6-chip hybrids
1 4-chip R-F hybrid
1 4-chip stereo hybrid
No opens or shorts caused by bonding

4. Hybrid Thermal Cycler at UCSB (2)
Scope mode (25 ns between each acquisition)
Opens added to hybrid to test PA pulser
Opens clearly seen in both scope mode (above) and pedestal tests (below)
Should have no problems detecting problems in hybrid bonding
All 4 chips shown here

5. Modules Produced with Final Hybrids
First Stereo TOB module made!!!
3 TOB stereo module produced in total
All well within specs mechanically and all Grade A
Kapton circuit was missing a trace for bias. We made it by hand with Ag Epoxy.
One chip has dead pipeline column
Found to be dead prior to module production
2 TOB 6-chip R-F module produced (first module of this kind produced!!)
Both Grade A
1 TOB 4-chip R-F module with final hybrid built
Grade B due to known sensor faults

6. Dead Pipeline Column (1)
Chip with unusual pulse shape and pinhole tests found (see next slide)
After conferring with Aachen and CERN, problem appears to be confined to one pipeline column
After taking a pipeline test with many events, it became clear that the noise of a pipeline column was too low to be active (Dead pipeline column)
Noise is lower than APV in bare hybrid

7. Dead Pipeline Column (2)
Other symptoms of dead pipeline columns
Pulse Shape Test
No calibration injection 0.5% of events
Causes dips in pulse shapes
Pinhole Test
1 in 192 chance of having no calibration injection, causing channels to be marked as pinholes
Need to modify hybrid testing procedure to find dead column prior to module assembly
Measuring pulse height in pipeline-like test with calibration injection would find this problem 100% of time
Problem is not serious enough to cause rejection of module
~ Equivalent to dead channel

8. Module Cold Box Status All functionalities demonstrated (UCR/UCSB)
Cold box fully instrumented
10 UTRI, 10 PAACB, FED multiplexer, 2nd CCU and electrometers
Works with multiplexer, electrometers and PAACBs
Performed long term module tests during production run with full readout of temperatures and currents
Since September CMS week
Implemented grounding scheme to reduce noise greatly with multiple modules
Conducted first backplane pulse tests

9. Module Cold Box Noise at UCSB
Before
After
High noise on all 8 slots tested
Grounded hybrid-to-UTRI adapters to cold box plates.
Noise reduced on all slots enough for defects to be seen.
Both at UCSB and FNAL

10. Backplane Pulse Test in Cold Box
Shorted to two channels
Open (to remove short)
Open
Open
Open (to remove short)
Shorted to two channels
Module 1025 noise with 100V bias
Module 1025 backplane pulse response with 100V bias
Channel with marginally low noise shows up clearly in backplane pulse response
Successfully tested in LT version 1.15 (needed upgrade from 1.10)

11. Single Rod Test Stand at UCSB
Complete set of electronic ready to test single rods
Test box provides dry, dark, and electrical isolated environment
Connects to Rod burn-in chiller for cooling
Prototype rod with 3 biased modules tested on stand

12. First Assembled Rod in US
First rod in US fully assembled
Took approximately 2 hours for assembly
Electrical tests have just begun

13. CMN Problem
14 of 60 modules produced at UCSB exhibit large common mode noise (one chip only)
All of the 14 modules have a larger bias current than expected from sensor QTC probing
Extremely high noise on 1-4 channels on each module suggests all the excess current localized to these channels
No obvious damage seen on these channels (visual inspection)
No indication of problems seen in sensor QTC measurements
At UCSB, problem always appeared at first test after bonding
1 module at FNAL developed problem during Wien box module burn-in after a full ARCS module characterization

14. Why be concerned about CMN problem?
One can argue that this may not be a real problem for several reasons:
It is mainly occurring at high bias voltages
It causes only a small amount of Common Mode Noise (CMN)
The noise is removed by CMN subtraction in the FED.
In fact we see evidence that all of the above are not quite right: (see discussion below)
It may be that more sophisticated CMN removal algorithms are needed and hopefully the FED is capable of running them
It may be that the new ST sensors have a drastic reduction in this problem
Study of 102 recently produced ST sensors sent to the US (thanks Manfred et al.) gives indication that problem is less severe in new production
In addition, CMN problem developed in 1 FNAL module during burn-in
Not clear how the problem will develop during operation

15. CMN Turn-on Voltage

16. Common Mode Subtracted Noise
25 ADC
6.5 ADC
Off scale 
Off scale 
Module #:
(Peak Off)
Chips with CMN (micro-discharge problem)
Common mode subtracted noise in blue
For majority of modules with problems, the CM subtraction is imperfect.
7 of 12 have >2.0 ADC noise
3 of 12 have more than twice the usual noise

17. Common Mode Subtraction Variation
Module 1010
Module 1016
Common mode subtraction results clearly vary
Answer differs mode-to-mode or test-to-test
Would yield varying signal efficiency/noise during data taking
Not clear how this will evolve with time/radiation

18. Module 705 before LT (FNAL)
After assembly module was tested (09/08) on ARCS at 400 V and graded “B” (6 faulty channels). No problems observed.

19. Module 705: LT data (FNAL)
Data was taken at 20°C on Sept.19 (10 days after the first test). A group of high noise channels is seen around channel 219 and increased CMN is seen in chip #2

20. Module 705 after LT – I (FNAL)
Module was re-tested on ARCS on 09/23. High noise in channel #219 and high CMN is observed at 400 V. At 200 V channel #219 has only slightly higher noise than the rest of the channels
400V

21. Module 705 after LT – II (FNAL)
On ARCS kept module at 400 V for 30 minutes before testing (to allow current settle down)
CMN did not go away, it became even higher

22. Comparison of IV curves (FNAL)
”before” measurement is taken on 09/08 on ARCS before LT
“after” measurement is taken on 09/23 on ARCS after LT
green curve is a measurement done using Keithley on 09/24 with 1 minute interval between steps
No visual defects are observed on the sensors around noisy channel #219
At this point we can’t conclude whether the effect we observe is due to thermal cycling or if it is some other effect

23. Studies to determine origin of CMN problem
3 FNAL CMN problem modules sent to Karlsruhe for irradiation studies
See talk by F. Hartmann
Extensive program of sensor probing and additional module IV measurement undertaken
Sensors probed prior to assembly in modules
Sensors with >5 mA extra current relative to sensor QTC measurement separated from others
Module then assembled and bias bonded to first sensor
IV measured
Bias is bonded to second sensor
IV remeasured
Module is then fully bonded and tested

24. Sensor Probing Three Sets of Sensors Probed
Old OB2 (Week to Week )
75 Sensors
Old OB1 (Week to Week )
31 Sensors
New OB2 (Week )
97 Sensors
Environmental conditions tightly controlled
Temperature C
RH < 30% at all times

25. Results of Probing Study - UCSB (1)
22 modules produced and bonded prior to change in procedure
4 had CMN problem
6 modules produced were IV measured prior to sensor bonding, but sensors not probed
5 show greatly increased bias current prior to bonding of channels
Bonding is NOT source of problem
32 modules produced with sensor probed at UCSB
5 built with sensors with increased bias current (>5 mA)
4 show CMN problem
27 built with sensors with IV matching sensor QTC measurements
Only 1 shows any indication of CMN problem
Only appears in ~50% of test
Problem appears to originate prior to module assembly
The sampling of sensors was slightly biased toward high-fault rate sensors.
Almost all from old OB2 batch.

26. Result of Probing Study (2)
Probed UCSB (450 V) – QTC Measurement (450 V)
Sensor Group
> 2 mA
>5 mA
>10 mA
>20 mA
>100 mA
< -2 mA
<-5 mA
<-10 mA
Old OB2
15% 9% 8% 5% 1% 3%
Old OB1 6% 0%
New OB2 2%
We observed that a bias current increase of ~5 mA can cause common mode noise
Rate of CMN problem consistent with percentage of old OB2 sensors this increase
UCSB probing agrees much better with new OB2 sensors!!!!
Produced Week of 2002
Factor of ~4 decrease in the rate of higher and lower current measurement at UCSB relative to old OB2 sensors
We need to measure sensors after all processing changes were made to confirm these result ASAP!!!!

27. Preliminary Conclusions (1)
The CMN problem appears to be a sensor problem
It is NOT created during module assembly or bonding
The cause of the problem is NOT clear
No visible damage or indication of defects from sensor QTC
Pre-screening sensors (measuring IV) in US appears to improve situation greatly but:
We do NOT know how the problem will evolve
Rate of appearance vs. time, power cycles, etc.
Changes with radiation damage
How problem parts will act with in sub-structures with final electronics and power supplies
Can only make ~9-12 sensor IV measurements per hour at assembly centers
Would need 1-2 full-time techs for this alone at peak production
Doing it somewhere else would even be better
While improvement in newest batch of sensors probed were seen, we cannot rule out the possibility of having a FRACTION of effectively dead chips in the TOB and outer TEC until problem is better understood

28. Preliminary Conclusions (2)
We really cannot do much more to study this problem at UCSB/FNAL
Hopefully we have provided enough information to Sensor Group to continue study
See irradiation/probing studies by Karlsruhe
Looked into studying modules with IR camera
2 private companies found in Bari and in San Diego which can study parts with their equipment and our expertise
No idea of cost
2 companies identified which sell cameras-OptoMetrix and QFI
Cost about $80,000 for full system
Karlsruhe has partial system
Need camera and IR lenses (>$30000)
Hiroshima University has a system which we may use there
Really need a Sensor Group contact to continue study
Do not have man-power for this and other responsibilities