P. Béné, F. Cadoux, A. Clark, D. Ferrère, C. Husi, M. Weber University of Geneva

IBL General Week - 11, 12 February 2010

IBL Stave Loading Status

Summary of the activities at UniGe:- Stavelet program for thermal interface investigation- Electrical insulation of module versus stave

Stavelet – Loading with glue/grease test program

Purpose of the tests – glue versus grease:• Selection of candidates according to past experiences, thermal performances, viscosity, …• Evaluation of weight versus area• Optimization of the glue/grease dispensing technique (no glue overlap between the 2 chips)• Thickness uniformity and placement accuracy – XYZ metrology • Robustness to thermal cycling – XYZ metrology • Rework ability?

Removal and evaluation of time and risk for this operation Inspection of neighboring module edges Inspection of remaining surface loading again

• Does the use of Parylene® coating make a change?• Practical use

Independent tests to the stavelet program:• Radiation hardness of the glue and grease samples – Thermal performances, consistency…• Glue and grease mechanical and thermal characterizations• Others…

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Gluing and grease test program on C-foams stavelets

~20 mm

~150 mm

Glass pieces loaded with glue and or grease and various patterns

Glass references:- Glued on the 2 sides- Height > glass thickness- Hole for XY metrology- Top surface for Z plane

NB: Assembly of the 3 washers as much as possible in the same plane

Glued holding bar Glued holding bar

Procurements:- Glass pieces (20x40 mm2)1 or 2 mm thick to be cut by a diamond tip CERN stroe + cutting UniGe- C-foams to be coated with parylen. 1 or the 2 sides? Samples to be cut at UniGe + Comelec (coating) – C-foam in 0.25 g/cm3, 0.5g/cm3 et 0.9g/cm3

- Holding bars made of aluminum or plastic to be butt joined to the C-foam UniGe- Mechanical washers to be made & glued UniGe- Glue and grease candidates To be discussed with Marseille and IBL stave WG- Jigs to handle and load the glass pieces on this stavelet To be made by UniGe with the corresponding threads for the holding bars and placement accuracy- Tungsten wires for the rework with glue

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Assembly jig allowing to glue the aluminum ends, but also the dummy glass modules

Features to reference the dummy glass modules

Area to glue gleass fiducial marks

Stavelet Jig Designs

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Stavelet Jigs

Stavelet assembly jig

Stavelet jigs for metrology, thermal cycling, storage

Features for dummy module assembly references

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Glass Pieces Under fabrication

40

20

10

10

Dum

my

Glas

s Mod

ules

with

Fid

ucia

l Mar

ks

Glass pieces for Jig References

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Carbon Foam Electrical Insulation using Parylene® Coating – Investigation for IBL Stave

Concerns:- Carbon foams are electrical conductive materials- IBL module require an electrical insulation for the FEI4 backplane but as well as for the detector HV- Depending of the detector technology the potential at a distance of 300µm from the foam can be as high as 1000V.- Bare foams can easily release carbon dust that could cumulate and be oriented into the electric field and therefore reduce the insulating distance

Proposal is to use of a thin coating like Parylene® allowing:- To prevent electrical problems and limiting the thermal resistance- To contain and avoid releasing carbon dusts

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Pictures of the Foams under a MicroscopeCarbon Foam 0.25g/cm3 – No Parylene POCOFoam 0.55g/cm3 – No Parylene

POCOFoam 0.55g/cm3 – 5 µm Parylene POCOFoam 0.55g/cm3 – 20 µm Parylene

NB: No coating was made for carbon foam 0.25 (No sample available)

Mag

nific

ation

x10

0

500 µm 500 µm

500 µm 500 µm

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Set-up – 1st Testing Step

- Cupper foils were directly in contact with the foam samples- 3 samples tested for the resistivity (non coated, 5µm and 20µm)- 2 samples tested for HV insulation (5µm and 20µm)

HV

HV GND

Foam sample

insulator

insulator

Clamp

Clamp

Tested samples: POCOFoam ®Test setup: Coated foam samples clamped between 2 cupper foils and connected to the 2 HV polaritiesPressure to the coated surface: Unknown but not null

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Parylene® Coating Insulation to contact Breakdown Voltages [V]

No No 0

5 µm Yes 550 (over 10 microns)

20 µm Yes 1100 (over 40 microns)

Comments: The coated (5-20 microns) foams does not release any visible carbon dust.

Set-up pictures and Results

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Pictures after Electrical Breakdown

NB: Breakdown possibly occurred where the clamps were applying the highest pressure

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Second Testing Step with Shims

Electrical insulation in a new test conditions:- With 400µm gap between the cupper and the foam- Various samples: non-coated, 5µm and 20µm

HV

HV GND

Foam sample Insulating shims (~400µm)

Plastic stiffener

Plastic stiffener

Clamp

Clamp

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Set-up Pictures and Results with Shims

Parylene® Coating Breakdown Voltages [V] Equivalent insulation for 300µm air + coating

No 1100(over 800µm air)

400 V

5 µm 2400 (over 10 µm + 800 microns air)

1050 V

20 µm 3300V(over 40 µm + 800 microns air)

1500 V

NB: - Safety factor should be applied to the limit to get guaranty on long term QA- Considering a safety factor , the current design is acceptable with 10-20 µm Parylene®

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Pictures – Copper after Electrical Breakdown

5 µm Parylene 20 µm Parylene

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Si-detector backplane

Edge chipping and Si-debris often seen pointing in all directions

Additional Comment

Observed during SCT production and QA

Stave coating is clearly an advantage in such a case even for backplane/edge voltage like 100V

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Summary

• Stavelet Program - Goal is to test various thermal interfaces to evaluate the practicality for loading, the thermal stability, the weight, the rework-ability - Thermal evaluation of a selected grease interface will be done with dedicated thermal set-up- Time scale: ~3 months

• Module to stave electrical insulation- Parylene® coating have been made on POCOFoam samples: 5, 10 and 20 microns- Coating almost invisible under the microscope- No carbon dust release when touching the samples with the fingers- In IBL condition with ~300µm gap from the sensor edge to the stave it will be risky to operate it without an insulating coating. - The preliminary recommendations from this test is to coat the stave with 10 to 20µm Parylene®.- Remaining question: Is this 10 to 20µm enough when considering the aging, and the radiations

• Stave loading concept- Close connection between CPPM and UniGe- Common concept with a cradle and a manipulator- Progress to be made with a nominal stave design

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