M. Gilchriese Pixel Stave thermal/mechanical studies for Valencia Upgrade Workshop M. Gilchriese, M. Garcia-Sciveres, M. Cepeda LBNL W. Miller and W. Miller, Jr iTi

M. Gilchriese 2 Introduction Studies of single layer stave support and monolithic structure Layouts based on possible B-layer implementations Construction uses carbon foam and round Al pipes. –Round tube embedded in low-density conducting foam + very thin “skins” of carbon-fiber laminates(eg. K13D2U) –Why round tube? Would allow full-pressure testing with gas(not possible in current detector). –Why foam? Versatile. Low-mass. Compatible with both monolithic and stave-based designs. FEA mechanical and thermal analysis Prototype of single stave section (measurements in progress) Generally assume a “spec” thermal load of 0.6W/cm 2

M. Gilchriese 3 Integrated Monolithic Option Support split into two halves 35 mm radius inner stay clear Low density foam structure with thin(125 micron) skins on inside and outside(makes shell). Heat load assumption for 800mm length=120W Two pass for each cooling tube: 5mm ID to limit pressure drop to <200mbar 88mm 37.5mm 24.4mm

M. Gilchriese 4 FEA Studies See backup for most details and figures Gravity sag over 800 mm length: about 3 microns Distortion from cooldown(  T=50C): <10 microns Thermal performance –Tube wall -22C –CGL7018 coupling tube to foam –Detector temperature -18 to -15 –Note red is IC “overhang” Proof-of-concept -17.8ºC -15.6ºC Center detector more representative

M. Gilchriese 5 Possible monolithic development Shared cooling tubes => lower mass Also smaller radial envelope Note half of the modules are “outside”.

M. Gilchriese 6 Stave Design 1 Concept –Retained features of integrated design, same cooling tube size –Less foam, but added cylinder –Outer diameter ~93mm –Inner diameter 70mm

M. Gilchriese 7 Stave Concept 1 for B-Layer Replacement Half-length shown

M. Gilchriese 8 Stave 1: Basic FEA Configuration Effects simulated –Mass of coolant, average density 145kg/m 3 –Laminate, 2 layers 2.5mil, 0/90, K13D2U Radiation Length estimate=0.532% –Foam=0.11% –Tube=0.3% –Composite=0.11% – Coolant=0.012% 5mil laminate 5.6mm OD tube 12mil wall 0.5mm of silicon to simulate chips and detector Also 0.9 mm of Kapton cable for additional mass

M. Gilchriese 9 Second Configuration-Stave 2 Goals –Reduce tube size and amount of foam material –Analytically evaluate impact on thermal and mechanical design OD=88 mm ID=~69.75mm

M. Gilchriese 10 Stave 2: With Offset Mounts Space on back-side next to mounts appears adequate to place cable, for wrap-around mounting Cable position (for thermal analysis) Potential cable location

M. Gilchriese 11 Stave 2: With Offset Mounts Cable Illustration –Back side, thin bonding wraps around –Cable on back-side becomes thicker as the stave end is approached Cable constant thickness in this region

M. Gilchriese 12 Stave 2: Gravity Sag Upper Stave position near vertical centerline –Modeled ½ length, from mid plane of symmetry of a 778 mm long stave –Model provides effect of a 5 point support stave length Resulting gravity sag 0.41microns Does not include support shell sag

M. Gilchriese 13 Stave Concepts - FEA Summary Stave 1Stave 2Comments Gravity SagNegligible <0.1µNegligible <0.5µDoes not include shell sag! 5-pt support Cooldown distortion <6 µ out of planeAbout 50 µ50C change Stress in foam- tube interface 300 psi145 psi50C change. Does not include glue compliance  T(C)-no cable About 5 Tube at -22C  T(C)-with cable on front About 6 Worst case?

M. Gilchriese 14 Development Work Carbon foams with good thermal conductivity, but significant density, are available from multiple producers POCO foamPOCO foam: eg.  = 0.55 g/cc and K(out) 135 and K(in) 45 K-foamK-foam: eg.  = 0.34 g/cc and K(out) 55 and K(in) ? We have, in fact, made staves with POCO foam/round tube as part of upgrade R&D for outer silicon tracker. We have now worked with company to make samples with  about 0.15 g/cc and K of about 45(isotropic). In future, are hoping to also investigate carbon nanotube(CNT) loaded materials with same company and perhaps CNT “cloth” under development for heat spreaders for ICs. CNT have very high K along tube direction >1000.

M. Gilchriese 15 Pixel Stave Prototype Development Thermally conducting foam obtained from Allcomp, Inc –0.18 g/cc as delivered –Thermal conductivity not measured (yet) Small prototype (20 cm long and about 2.4 cm wide) made – see photos on next pages –Small aluminum tube(2.9mm OD and 2.3mm ID) used to simulate about what might be used for CO2 at SLHC –Foam machined (easy) to shape and with groove for tube –CGL7018 used to couple tube to foam –Hysol 9396 loaded with Boron Nitride (30% by weight) used to couple facings to foam One facing is YSH70 cloth, 140 microns thick Second facing is K13D2U 4-ly laminate 300 microns thick ( orientation)

M. Gilchriese 16 Pixel Stave Prototype - I Foam with groove for tube. Three pieces joined. One side YSH-70 cloth K13D2U laminate

M. Gilchriese 17 Pixel Stave Prototype - II Tube with CGL7018 YSH-70 and K13D2U glued to foam Tube in foam with CGL7018

M. Gilchriese 18 Pixel Stave Prototype - III Final assembly(foam+fiber halves glued together around tube) Heaters on YSH-70 side only for first measurements Platinum-on-silicon heater in middle to simulate pixel module and copper-kapton heaters on either side to minimize end effects. 6.9 mm 24 mm Foam 260mg/cm 2 (exc. Pipe) => 130mg/cm 2 for

M. Gilchriese 19 Thermal Performance IR camera used Water coolant at 1.0 l/min at 20C. Vary power level in silicon heater And separately in copper-kapton heaters to about match Power/Area LabelEmisBGAveSDMaxMinUnit A C A C T in boxes

M. Gilchriese 20 Preliminary Thermal Performance Note if CO2 used as coolant then reference temperature could be about -30C. Thus delta T of 10 => T of -20C. FE-I4 goal FE-I3 normal Max. spec    Includes sensors & power conv. But not cables.

M. Gilchriese 21 Conclusion Integrated monolithic concept appears to be structurally and thermally feasible Multiple stave concepts developed and also feasible (no surprise) All based on edge-to-edge modules (no shingling). Low-density, thermally conductive foam with very thin carbon- fiber facings appears to be feasible approach mechanically and thermally. First prototypes made and validation in progress.

M. Gilchriese BACKUP

M. Gilchriese 23 Integrated Monolithic Structure

M. Gilchriese 24 Integrated Structure Assumptions Split Structure –Sandwich structure, with cooling tubes embedded between 2-layer composite facing Composite laminate produced using K13D2U fibers and Cyanate Ester resin –5mils for two layers (0/90) 5 mm ID Aluminum tubing, 12 mil wall (~5.6 mm OD) FEA Structural Model –Tubes and foam core treated as solid elements Mass of coolant, average density 145kg/m 3 –Outer surface laminate: used laminate element, with single material –Inner surface (saw-tooth) contain laminate elements with material designations for: Composite layers (0/90) Silicon module assembly, 0.5mm silicon Cable, 0.9mm uniform along length

M. Gilchriese 25 Gravity Sag Model based on 1G loading vertical –Sag measured in local coordinates –T1: translation is vertical along shell split plane –Maximum sag ~2.8microns –Model length 800mm 2.8 μm

M. Gilchriese 26 Thermal: 50C Temperature Change Y Thermal strain due to cool-down –Local coordinates, T2 is transverse to vertical plane of symmetry peak shape change is 5.5microns –Model length 800mm Unfortunately the out- plane distortion is a combination of T1 an T2

M. Gilchriese 27 Thermal: 50C Temperature Change X-Direction Thermal strain due to cool-down –X: direction 8.2 to 6.6 microns X is split plane, using symmetry boundary conditions –Model length 800mm

M. Gilchriese 28 Pixel Thermal Solution-Integrated Structure Description –Isotropic carbon foam: 45W/mK Specialized low density (0.21g/cc) foam: enhanced to high conductivity –Includes 5mil laminate thickness –Detector 250microns –Chips 200 microns –Bump bonds 25microns –Interface resistance from bonding chip to foam equal to 0.8W/mK; 4mil thickness (CGL7018) –Pixel chip heating: 0.51W/cm 2 –Simulated tube wall -22ºC Results –Peak chip edge: ºC –Detector ranges from-15.6 to ºC -17.8ºC -15.6ºC Center detector more representative

M. Gilchriese 29 Stave Approach

M. Gilchriese 30 Stave 1: Gravity Sag Upper Stave position near vertical centerline –Modeled ½ length, from mid plane of symmetry of a 778 mm long stave –Model provides effect of a 5 point support stave length Resulting gravity sag 0.085microns Does not include support shell sag

M. Gilchriese 31 Stave 1: Thermal Distortion Cool-down effect: 50°C Delta –Most of distortion is contraction along stave length –Distortion T2 is out-of-plane –T2 peak distortion is 5.6microns

M. Gilchriese 32 Stave 1: Thermal Strain Stress in Foam/Tube Interface –Evaluated without compliance of bonding adhesive (CGL7018 type) –Contraction of Al tube produces local stress of 300psi at interface Effect best evaluated through testing –Plan is to use special Reticulated Vitreous Carbon Foam with enhanced thermal and mechanical properties Solid Von Mises Stress

M. Gilchriese 33 Stave 2: Thermal Solution-With Cable Cable heat load –Adds a heat flux of 0.1W/cm 2 to the 0.6W/cm 2 chip heat load –Gradient before was 4.99 º C, detector middle to tube inner surface –Would expect gradient of 5.82 º C now –Gradient now from detector middle to tube surface is 6.0 º C Cable surface –Peak º C, or a ΔT=7.9 º C –Peak affected by K assumed for the copper/Kapton cable Used 0.35W/mK, whereas Kapton alone is 0.12

M. Gilchriese 34 Stave 2: Gravity Sag-Off Set Mount Effect on rotation of stave –Maximum rotation 1.9 μradians due to sag

M. Gilchriese 35 Stave 2: Thermal Distortion Stave with out-of-plane bending due to cool-down 50°C –Modeled ½ length, from mid plane of symmetry of a 778 mm long stave –Model provides effect of a 5 point support stave length Resulting bending 51.5 microns

M. Gilchriese 36 Stave 2: Thermal Strain Stress induced by contraction –Less than in Stave 1 geometry –145psi, more localized at ends –Be mindful that compliance of adhesive not present

M. Gilchriese 37 Stave 2: Thermal Solution Model Parameters –Carbon Foam, 45W/mK –Composite Facing, K13D2U-55% vol fraction 0/90, K t =0.55W/mk, 220W/mK planar (no axial thermal gradient so this parameter is not an issue) –Chip 0.2mm –Bump bond thickness,.05mm –Detector, 0.25mm Adhesives –Tube to foam, 4mils, 0.8W/mK –Foam to composite facing, 2mils, 0.8W/mK –Chip to composite facing, 4mil, 1.29W/mK –Cable to detector module, 2mils, 1.55 W/mK

M. Gilchriese 38 Stave 2: Thermal Solution-No Cable Coolant Tube boundary condition –-22 º C Chip Heat Flux, 0.6W/cm 2 Detector Temperatures –Left edge, º C –Middle, º C –Right, º C

M. Gilchriese 39 Stave 2: Thermal Solution-With Cable Thermal plot with cable removed –Illustrates comparative uniformity in detector temperature

M. Gilchriese 40 Detector Temperature Summary Thermal Solutions for two designs, but unfortunately different detector layouts –Integrated, different by chip over-hang –Stave-like, provides complete coverage Two different foam/sandwich structures, one with less material analyzed first With time will bring configurations into consistency However, the predicted detector surface temperature for each is: –Low-mass stave without cable heat load, -17 º C –Low-mass stave with cable heat load, -16 º C –Integrated Foam/Tube Support without cable load, º C Caution, as analysis proceeded slightly more conservative properties were used for the composite facing and the foam: –Facing 0.55W/mK versus 1.44W/mK –Foam 45W/mK versus 50W/mK

M. Gilchriese 41 Bare Module Dimensions mm Active area mm mm Footprint mm stack 200um chip 20um bumps 250um sensor Module power load: 1.25W => 0.4 W/cm 2 but we use 0.6 W/cm 2

M. Gilchriese 42 Stave Arrangement Modules abut one against the next. Flat stave surface! 48 modules per stave for 778mm total length. Readout/power from both ends.

M. Gilchriese 43 Option 1: Module with Flex Cable 14mm 500mm Flex cable 0.075mm 0.97mm Cable power load: 0.4W (uniform over full 50cm)  Each module has a pre-attached, full length cable  All cables are identical and are cut to length during module attachment

M. Gilchriese 44 Option 2: Cable(s) pre-laminated on back of stave  Flex would be laminated to back side of stave and tested before modules are added  A flap at each module location is bent around and to the top of the module and wire bonded after the module is loaded.  A single 2-sided copper cable could be used to route all the signals. Multiple aluminum on kapton planes could be laid up on top of that to build up power bussing, bonding each one down to the copper flex to get the power to each flap.  Recall all this is built and tested before modules are added, so repeated gluing and wire bonding are not an issue.  Assume same cable power load as for option 1.  A stave control card would be loaded at the stave end as for option 1 Signal cable with 24 flaps before lamination. Could also be multiple cables. End of stave card could be built-in