Velo Module 0 minus minus

Paula Collins

Investigating Module 0 thermal performance

Baseline module design combines elements of different CTE (and Young’s Modulus)

Can the elements stand the strain? What about the bump bonds? What about repeated thermal cycling (-40 →+20 oC)?

Is the thermal performance in vacuum as expected?

Different approaches are possible to optimise (flexible glue, splitting silicon into smaller pieces)

Kapton: 30-80 10-6 C-1

Silicon: 2.8 10-6 C-1

Diamond: 1.5 10-6 C-1

Thermal Performance and Simulation

Power consumption varies as a function of lifetime

~ constant in chips: 0.5-? W/cm2

Silicon rises to ~0.3-0.5 W/cm2 in the part most remote from the cooling

See presentations of Steve Blusk and Brian Maynard from upgrade meetings for more details

0.0

0.2

0.4

0.6

0.8

1.0

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0 10 20 30 40 50Distance from beam (mm)

Po

we

r/A

rea

(W

/cm

2 ) at -25 C

at -15 C

at 0 C

Chip power W/cm2

Ultimately the cooling attachment will be a huge challenge

Second stage of mechanical tests would be to investigate different methods of cooling pipe attachment

Could be clamped between additional diamond pieces

Or could go for ATLAS style approach: use RVC foams to couple round metallic tube to rest of structure

Use of small glass capillaries has been suggested by Nikhef

2 diamond piecesEnclose in CF frameCooling pipe around the edgeOrOne TPG core large hybrid?

Bus cable

Hybrids Coolant tube structure

Carbon honeycomb or foam

Carbon fiberfacingReadout

IC’s

Silicon sensors

Properties of Thermal GreaseExtensively studied for ATLAS and CMS upgrade (both strips and pixels)• >8 different compounds tried by ATLAS (dow corning, wlpg, cgl 7018 etc.• http://cdsweb.cern.ch/record/1238166/files/ATL-UPGRADE-PUB-2010-0

02.pdf• Example candidate for foam development is Allcomp, Inc but lots of R&D

even for non vacuum environments – lowering density of graphitic foams, increasing density of RVC foams etc. etc.

• No need to reinvent the wheel, but have to try things out in our scenario…

Some strain could be taken up in the glue

“Fluid Glues” exist and can be tried:• Dow Corning 734RTV (tens. strength= 16 Kg/cm2, 321%

elongation, CTE~300 10-6 C-1, er~2.5, dielectric rigidity~18KV/mm

• Epotek 353ND (flex. strength= 750 Kg/cm2, CTE=56 10-6 C-

1, viscosity = 2000 cps)

Other things to watch for: radiation resistance, outgassing properties, thermal conductivity

In view of the cost of the diamond.. Dismountable tests?

Maybe a hard glue needed for a one sided firm connection e.g. cyanoacrilate.

CERN interestWe are interested in procuring piece(s) of diamond from Diamond Materials and testing various aspects of the module 0 construction.

The initial try for the shape would be the rectangular 3x2 chip piece, plus a margin on 3 sides to allow for potential cooling pipe attachment

Initial thickness: 200 micron

Interest in mechanical and electrical tests7

Vacuum test stand developmentRaphael Dumps

Vacuum test stand essential for LHCb (and possibly other groups)

Design is in progress• Incorporate germanium window

and camera• Position measurements• Peltier cooling• High speed feedthroughs• Inerchangeable flanges for testing

different modules

8

Mechanical testsVerify planarity and surface roughness of diamond• Use of scanning EM at CERN metrology department

Populate with 6 pieces of silicon and heater chips (total thickness 300 micron), and temperature measuring sensors

First cooling try to tie back edge and sides to a plate of fixed temperature

Later can try various methods of attaching cooling pipes and mount in vacuum tank

Heat with various powers, and cooling temperatures and compare the temperatures achieved with the thermal simulations

Practice measurements of temperature with the thermal camera and deflection

Thermally cycle and check for damage

If severe deflections are seen, we possibly can try to attack this with structuring the diamond (e.g. grooves)• CERN has measurement devices for cryogenic tensile testing

9

Stage 0 minus one test300 um thick silicon piece glued onto diamond and instrumented with smd components to allow uniform and non uniform heating

Glued to diamond cooling plane

Loosely clamped with a lot of thermal grease to Peltier cooled heatsink

Possibility to mount assembly inside vacuum tank

Electrical testsOne piece of diamond to be instrumented as a timepix readout

See if a standard timepix planar silicon assembly can be read out via diamond metallisation lines

Check on issues such as metal deposition, reliable attachment of connectors, bonding issues, and thermal interface

To be done in collaboration with CERN PCB workshop

Device can go to testbeam and also be irradiated

First step will be to thermally cycle and check bump bond integrity

11LHCb VELO Upgrade MeetingApril 14th 2010 - Paula Collins

Irradiation tests (Phil, Jan, Maurice)

Diamond pieces are being irradiated

The evolution of the thermal conductivity will be checked

A number of samples will be irradiated in parallel and removed after a certain time

The performance will be calibrated against a non-irradiated piece

12LHCb VELO Upgrade MeetingApril 14th 2010 - Paula Collins