# Presentation: 125089

## Pixel Stave thermal/mechanical studiesfor Valencia Upgrade Workshop

- M. Gilchriese, M. Garcia-Sciveres, M. Cepeda
- LBNL
- W. Miller and W. Miller, Jr
- iTi

## 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/cm2

## 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

## 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

## Possible monolithic development

- Shared cooling tubes => lower mass
- Also smaller radial envelope
- Note half of the modules are “outside”.

## Stave Design 1

- Concept
**Retained features of integrated design, same cooling tube size**
**Less foam, but added cylinder**
**Outer diameter ~93mm**
**Inner diameter 70mm**

## Stave Concept 1 for B-Layer Replacement

- Half-length shown

## 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

## 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

## 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

## 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

## Stave 2: Gravity Sag

- Upper Stave position near vertical centerline
**Modeled 1⁄2 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

## Stave Concepts - FEA Summary

|  | Stave 1 | Stave 2 | Comments |
| --- | --- | --- | --- |
| Gravity Sag | Negligible <0.1μ | Negligible <0.5μ | Does not include shell sag! 5-pt support |
| Cooldown distortion | <6 μ out of plane | About 50 μ | 50C change |
| Stress in foam-tube interface | 300 psi | 145 psi | 50C change. Does not include glue compliance |
| T(C)-no cable | About 5 | About 5 | Tube at -22C |
| T(C)-with cable on front | About 6 | About 6 | Worst case? |

## Development Work

- Carbon foams with good thermal conductivity, but significant density, are available from multiple producers
- _[POCO foam](http://www.poco.com/us/Thermal/foam.asp)_: eg.  = 0.55 g/cc and K(out) 135 and K(in) 45
- K-foam: eg. _[](http://www.kfoam.com/mainsite/index.htm)__[ = 0.](http://www.kfoam.com/mainsite/index.htm)__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.

## 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 (90-0-0-90 orientation)

## Pixel Stave Prototype - I

- Foam with groove for tube. Three pieces joined. One side

- Foam with groove for tube. Three pieces joined. One side

- YSH-70 cloth

- K13D2U laminate

## Pixel Stave Prototype - II

- Tube with CGL7018

- YSH-70 and K13D2U glued to foam

- Tube in foam with CGL7018

## 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/cm2
**(exc. Pipe)**

- => 130mg/cm2 for

## 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

- Label	Emis	BG	Ave	SD	Max	Min	Unit
- A1	0.95	19.0	27.41	0.65	28.4	25.9	C
- A2	0.95	19.0	27.36	0.80	28.4	23.8	C

- T in boxes

## 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.

## 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.

## BACKUP

## Integrated Monolithic Structure 

## 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 **

## 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**

- 2.8μm

## 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

## 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**

## 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/cm2
- Simulated tube wall -22oC
- Results
- Peak chip edge: -13.8 oC
- Detector ranges from-15.6 to -17.8 oC

- -17.8oC

- -15.6oC

- Center detector
- more representative

## Stave Approach

## Stave 1: Gravity Sag

- Upper Stave position near vertical centerline
**Modeled 1⁄2 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

## Stave 1: Thermal Distortion

_*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***

## 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

## Stave 2:  Thermal Solution-With Cable

- Cable heat load
- Adds a heat flux of 0.1W/cm2 to the 0.6W/cm2 chip heat load
- Gradient before was 4.99oC, detector middle to tube inner surface
- Would expect gradient of 5.82oC now
- Gradient *now* from detector middle to tube surface is 6.0oC
- Cable surface
- Peak -14.1oC, or a ΔT=7.9oC
- Peak affected by K assumed for the copper/Kapton cable
- Used 0.35W/mK, whereas Kapton alone is 0.12

## Stave 2: Gravity Sag-Off Set Mount

- Effect on rotation of stave
**Maximum rotation 1.9****μ****radians due to sag**

## Stave 2: Thermal Distortion

- Stave with out-of-plane bending due to cool-down 50°C
**Modeled 1⁄2 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*

## 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**

## Stave 2: Thermal Solution

- Model Parameters
- Carbon Foam, 45W/mK
- Composite Facing, K13D2U-55% vol fraction
- 0/90, Kt=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

## Stave 2:  Thermal Solution-No Cable

- Coolant Tube boundary condition
- -22oC
- Chip Heat Flux, 0.6W/cm2
- Detector Temperatures
- Left edge, -16.66oC
- Middle, -17.01oC
- Right, -16.78oC

## Stave 2:  Thermal Solution-With Cable

- Thermal plot with cable removed
- Illustrates comparative uniformity in detector temperature

- -15.57

- -15.94

## 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, -17oC
- Low-mass stave with cable heat load, -16oC
- Integrated Foam/Tube Support without cable load, -17.5oC
- 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

## Bare Module Dimensions

- 16.200mm

- Active area

- 17.500mm

- 16.210mm

- Footprint

- 19.000mm

- 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**_

## Stave Arrangement

- Modules abut one against the next.
- _Flat stave surface!_

- 48 modules per stave for 778mm total length.
- Readout/power from both ends.

## 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

## 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