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 o C)? Is the thermal performance in vacuum as expected? Different approaches are possible to optimise (flexible glue, splitting silicon into smaller pieces) Kapton: C -1 Silicon: C -1 Diamond: C -1

Thermal Performance and Simulation Power consumption varies as a function of lifetime ~ constant in chips: 0.5-? W/cm 2 Silicon rises to ~ W/cm 2 in the part most remote from the cooling See presentations of Steve Blusk and Brian Maynard from upgrade meetings for more details

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 pieces Enclose in CF frame Cooling pipe around the edge Or One TPG core large hybrid? Bus cable Hybrids Coolant tube structure Carbon honeycomb or foam Carbon fiber facing Readout IC’s Silicon sensors

Properties of Thermal Grease Extensively studied for ATLAS and CMS upgrade (both strips and pixels) >8 different compounds tried by ATLAS (dow corning, wlpg, cgl 7018 etc pdf 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/cm 2, 321% elongation, CTE~ C -1, e r ~2.5, dielectric rigidity~18KV/mm Epotek 353ND (flex. strength= 750 Kg/cm 2, CTE= 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 interest We 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 tests 7

Vacuum test stand development Raphael 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 tests Verify 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 test 300 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 tests One 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 11 LHCb VELO Upgrade Meeting April 14 th 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 12 LHCb VELO Upgrade Meeting April 14 th Paula Collins