# Presentation: 381948

## The D0 Run2b Silicon Stave Structure

*From material selection to performance verification*

- Giobatta Lanfranco
- Fermilab
- PPD/ Mechanical Department
- 2003, November 18th

## What is a «stave» ???

- STAVE =
- 	structure providing support and active cooling 	to the silicon sensors and their read-out 	electronics

## Outline

- Stave design
- Material investigation to satisfy design requirements and operating constraints
- Carry out extensive FEMs of the various material-design configurations
- Selection of best solution
- Testing
- FEA validation (trust the FEA to reduce minimize)

## Requirements

- Structural
-  60micron sag max in silicon
-  structure fundamental frequency > 60 Hz
-  Sensor core support < 50 micron flat
-  Low stress in silicon (prevents noise)
- Thermal
-  Silicon T < 0°C

## Why the Channel Design?

- Very stiff (the carbon fiber is right where you want it): ~50micron sag in operating conditions (145gr)
- Straightforward assembly process
- Sensor/hybrid accessibility and protection
- Cables support

## The Stave – exploded view

*Channels not shown*

- Axial modules

- Stereo modules

## Stave subsystems

- Silicon Sensors (4 modules)
- Hybrids
- 10 chips, mounted directly on the silicon sensors
- Channels
- Represent the stave structural part.
- Pin holders
- Align stave with the supporting bulkhead
- Interconnects the channels
- Core
- Flat bed for the silicon sensor (30microns achieved)
- Interconnects the channel
- Cooling line
- Embedded in the core
- U shaped
- Ethylene glycol 40% volume solution

## Materials

## Material Requirements

- High Radiation Hardness
- 10-30 × 106 rad
- High Radiation Length (Xo)
- No flame retardants (bromine-based) or other high Z materials (Z ≤ ZOxigen))
- C = 18.8cm, CF ~ 26-28cm,  Al = 8.9cm, Si = 9.36cm (but we can’t do without!)
- Elevated Bending Stiffness (EI) and Creep resistance
- Micron level positioning
- Low Outgassing
- Silicon CTE compatibility (bimetallic effect) is generally desired
- CTE Silicon = 2.49 × 10-6 ppm/°C @ 20°C
- To avoid warping and stress build-up (noise in Silicon)
- Low mass
- Lower gravity induced deflections
- Reducing inertia is also beneficial during silicon tracker transportation

## Core Materials - skin

| Materials Investigated | PROS | CONS | Choice |
| --- | --- | --- | --- |
| Kapton® MT | Relatively high K (0.36 W/mK (3×standard Kapton®)
Good epoxy adhesion
Excellent dielectric properties 
1 and 2 mils thick sheets available | Lowest Young’s Modulus (2.6GPa - but given the 20ppm/K isn’t it a plus?!) |  |
| Mylar® | Rigid (performs well for vacuum check)
Excellent dielectric properties 
Easy flatness achievable | Unacceptable epoxy adhesion |  |
| Impregnated Kevlar® 149 fiber | Good epoxy adhesion
Very High E (179GPa) | Difficult impregnation process
Poor flatness
 K = 0.04 W/m K |  |
| Impregnated Fiberglass E | Good epoxy adhesion
0.288 W/m K | Difficult impregnation process
Poor flatness |  |

## Skin Materials

- TEST: investigate peel strength and resistance to collapse under vacuum of the skin-tubing interface for leak checking

## Core Materials – “core core”

| Materials Investigated | PROS | CONS | Choice |
| --- | --- | --- | --- |
| Rohacell® 51 | Sheets with required thickness available
Extremely high Xo (~air!)
Low mass | Fragile
“Dusty”
Open cell (difficult epoxy mass control) |  |
| IM7/EX1515 Carbon Fiber frame | Rigid
 | Electrically conductive structure beneath the silicon sensor
Difficult assembly |  |

## Cooling Pipe Materials

| Materials Investigated | PROS | CONS | Choice |
| --- | --- | --- | --- |
| Aluminum |  Isotropic
 Relative easy bending
 Leak tight
 Predictable behaviour |  Galvanic Corrosion
 Low Xo
 Electrically conductive |  |
| PEEK® | High Xo
Corrosion resistant
Electric insulator
Pliable |  Hard T forming tuning
 Poor K (~0.12 W/mK)
 Helium permeable
 Collapses under vacuum |  |
| Carbon Fiber
[0/±45/0]
IM7 / EX1515 55gsm, 55micron ply |  Good Xo
 Stiff
 Easy leak check (no collapse under vacuum) |  Long R&D path (not leak tight) 
 Electrically conductive
 Non homogeneous
 Matrix is hygroscopic
 High wall thickness
 Electrically conductive |  |

## Channel Material - Fiber

## Channel Material – Resin System

| Materials Investigated |  | T 
[°F] | t [min] | Characteristics | Choice |
| --- | --- | --- | --- | --- | --- |
| Cyanate | RS-3 | 350 | 120 | good balance between toughness and high temperature/wet performance. 
Satellite, airframe/missile and dielectric structures |  |
|  | RS-12 | 265 | 300 | low temperature curing
Aerospace, radome, dielectric structures |  |
|  | EX1515 | 225-250 | 120 | Toughened, has ultra high conversion & high radiation resistance, fully self adhesive
Spacecraft and other Cryogenic Temperature Stable Structures, Reflectors & Radomes  |  |
| Epoxy | RS-7 | 250 | 90 | excellent balance of mechanical properties, toughness and modulus.  Sporting goods and aircraft structures  |  |
|  | BT-250E-1 | 250 | 60 |  MIL-R-9300 Qualified, 3 month out time @ room temperature
Secondary aircraft structures, Radomes, Sporting goods |  |

## Channel Laminate Lay-up Properties

| K1392U with epoxy resin BT250E-1
RC = 29.3% mass; 45 m thick ply
9 ply Lay-up: 0° ±45° [0]°3 ±45° 0°
density 1.727 gm/cm3 |  |  |  |  |  |  |  |  |  |
| --- | --- | --- | --- | --- | --- | --- | --- | --- | --- |
|  | GPa |  | GPa  |  | m/m K |  |  |  | W/m K |
| EX | 241.5 | GXY | 49.12 | X | -1.47 | XY | 0.89 | KX | 92.86 |
| EY | 44.63 | GXZ | 3.183 | Y | 2.671 | XZ | 6.8×10-3 | KY | 26.88 |
| EZ | 6.481 | GYZ | 2.373 | Z | 54.08 | YZ | 0.33 | KZ | 0.49 |

## Epoxies - Requirements

- Short curing time (productivity)
- Peel strength
- Wicking
- Accommodate CTE mismatches
- High purity for sensor gluing

## Epoxies... lots of applications, too many choices! (1/2)

| Epoxies | Main Application | Choice |
| --- | --- | --- |
| High Purity Epoxies (lower contamination levels of ionic and outgassing impurities) |  |  |
| Hexel 5313 + 3134 (hardner) | Silicon / hybrids mount |  |
| TDR 1100 | Silicon / hybrid glue joint. Cable on cable lamination. Very high peel strength |  |
| Araldite 2011 | Strong bonding to metals, ceramics, rubbers and rigid plastics. Sensors onto bus lamination |  |
| DP125 – EG 3M | Fast curing electronic grade, 25 minute worklife, very high peel strength. |  |
| Silicone based Glues |  |  |
| NE001 | Silicon onto carbon fiber mount. Absorb strong CTE mismatches |  |
| Dowcorning 3140 | Silicon onto carbon fiber mount. Absorb strong CTE mismatches |  |
| GE RTV 12 A+C parts |  Mixed with glass microspheres to thicken it. Silicon onto carbon fiber mount. Absorb strong CTE mismatches |  |

## Epoxies... (2/2)

| Epoxies | Main Application | Choice |
| --- | --- | --- |
| Structural Epoxies |  |  |
| DP-110 GRAY 3M | Strain relief protection. General applications that require fast curing times and good adhesion. Unlike many other fast cure two-part epoxies, this adhesive has excellent peel strength and shock and impact resistance  |  |
| DP-190 GRAY 3M | This adhesive has a 90 minute work life, with improved impact and shock resistance over many traditional epoxy adhesives. It is a 1:1 mix ratio of 2216 B/A Gray Adhesive. Channel-Core interface |  |
| 2216 3M  | Provides High Strength Bonds in Shear and Peel. Bonds Rubber, Metal, Wood, Plastic and Masonry. |  |
| Loctite 349 | UV adhesive. Modified Methacrylate Ester. Bonds and seals glass to glass, or glass to metal components such as precision optical instruments |  |
| HYSOL 9460 | High Peel strength |  |
| Electrical joint Applications |  |  |
| 2902 TRA-CON | Silver Epoxy |  |

## Stave Materials Properties – Summary

## Coolants

- Dowcal 10, ethylene glycol based, Dow Chemical Corporation
- Dowcal N and Dowcal 20, propylene glycol based, Dow Chemical Corporation
- Syltherm XLT, Dow Chemical Corporation
- 3M Fluorinert FC-77, C6F14 (FC-72) and C8F18, perfluorocarbon liquids, 3M Corporation

## Coolants Performance 1/2

- Velocity (U), mass rate (M), exit bulk temperature (Tb2) and temperature at the wall (Twall) given a 6psi pressure drop along the pipe.

## Coolants Performance 2/2

- Film coefficient (hc), Reynolds number (Re), Prandtl number (Pr) and Nusselt number (Nu) given the pressure drop along the pipe.

## STAVEFinite Element Analysis

## Stave Finite Element Model

| Material | Color code | Thickness [m] |
| --- | --- | --- |
| Rohacell | orange | 1000 |
| Kapton + epoxy layer | purple | 225
( p.g. + 50 ep.) |
| Silicon | Cyan | 320 |
| Patterned Glass + epoxy layer | Blue | 170
(120 p.g. + 50 ep.) |
| Glass | Light blue | 200 |
| BeO | Red | 380 |
| Gold / glass | Magenta | 210 |
| K139-BT250E-1  | green | 360 |
| Cooling tube
PEEK® | (not shown) | 100 |

## Deflection in the Silicon

- Units [mm]
- Restraints:
- 	z = 0mm, free to slide longitudinally
- 	z = 600mm, clamped

## Predicted T distribution in Silicon

-  q = 5W / hybrid
-  khybrid = 100.4 W/mK
-  Tb = -15°C
-  hc = 700W/m2K
-  Tube inner size: 7.2mm × 1.8mm

## Predicted Gravity Induced Stresses

- Stave total mass = 145gr
- Max sag = 49 m
*Notes:*
- (1) it keeps into account the peel strength in the kapton®-epoxy joint
- (2) Glass only property

| Material | Ultimate strength
Mpa | Predicted
Max von Mises stress
kPa |  |
| --- | --- | --- | --- |
| Silicon | 120
(208.9 ultimate bending) | 405.5 | 296 |
| Carbon Fiber | 126.7
(lamina max –S2) | 1761 | 72 |
| Rohacell® | 0.8 | 5.4 | 148 |
| Kapton/epoxy | 1.4 (1) | 93.3 | 16 |
| Patterned Glass | ~40 (2) | 95.3 | 420 |
| Glass | ~40 (2) | 58.0 | 689 |
| BeO | 135 | 172.2 | 784 |
| Gold / glass | ~40 (2) | 42.2 | 947 |
| PEEK® | 79.5 | 28.0 | 2835 |

## STAVE THERMAL TESTS

## Temperature sensors layout

## Thermal test – typical T profile

## FEA validationPredicted and Measured Temperature Profile for a Stave Mockup

## Stave Layers Thermal Resistance

*Comparison between the total heat leaving the stave (Q out), given as a function of the temperature difference between outlet and inlet, and the estimated heat entering the fluid (Q in_coolant) given as a function of the fluid bulk temperature and of the fluid temperature at the wall of the peek tubing. For every test condition (case 1 through 8), the fluid flow has been determined by two independent methods: 1) using the measured flow from the calibrated flowmeter (Gilmont correct) and 2) using the measured DP in the stave to calculate the flow through the tube cross section and the tabulated properties for ethylene glycol 40.6% volume *

## STAVE STRUCTURAL TESTS

## Strain and creep tests

- Point and quasi-distributed loading on D0 Stave

## Stave Deflection Test - 577.1 gr concentrated load

## Creep Test (8 weeks) - silicon surface150 gr quasi distributed load

## Summary

- Stave meets requirements
- Sag = 47.8 micron (!)
- Fundamental frequency = 91 Hz
- Max T on Silicon ~ -0.5°C
- Outstanding creep resistance (and @ room T!)
- Excellent structural and thermal FEA prediction
- Testing and analytical predictions must go together for a reliable and effective design

- And now...

- ANY QUESTIONS
- ???

## Formulas

## Deflection Tests on different configurations

## Understanding the Laminate Layout

- Extensional stiffnesses

- Coupling stiffnesses

- Bending stiffnesses

## BT-250E-1 Cure Cycle

## Hy-Bor®

- Boron Fibers (Hy-Bor®) have been investigated
- The CTE can be tailored to close match that of Si
- However
- _Low Xo_ (produced via chemical-vapor deposition using hydrogen reduction of Boron Trichloride on a tungsten filament in a glass tube reactor.
- 	2BCl3(g) + 3H2 (g) > 2 B (s) + 6HCl
- Do not allow to be bent around low radius corners

## Predicted and Measured Temperature Profile for the Stave Final Configuration

## Meaning of the non dimensional parameters: Re

-  Reynolds Number
-  is the density, *u* the velocity, *D**H* the hydraulic diameter and  the fluid viscosity. Re _relates the viscous and inertial forces_ _and determines the transition from laminar to turbulent flow_. For flow in long ducts, where the entrance effects are not important, the laminar region ends around _Re = 2320_; from 2320 to 10000 a transition from laminar to turbulent flow takes place, where the viscous effects become more and more important (*transitional regime*); after that the turbulent flow is completely developed.

## Meaning of the non dimensional parameters: Nu

- Nusselt Number
-  *k* is the thermal conductivity. Relating the film coefficient to the thermal conductivity of the fluid, _gives an indication of which heat transfer phenomenon_ – convection versus conduction – _is prevailing_ in the fluid and provides a direct way to calculate *h**c** *

## Meaning of the non dimensional parameters: Pr

- Prandtl Number
** is the kinematic viscosity, ** the thermal diffusivity and *Cp* the specific heat. Since ** can be seen as the molecular diffusivity of momentum, _Pr relates the temperature distribution to the velocity distribution_. So the temperature gradient at the wall will be steeper in a fluid having a large Prandtl number at a specified Re. Consequently also the Nu will be larger and the convection will be more efficient.

## PAN vs Pitch Fibers Technology

- PAN Type Carbon Fiber is excellent in elasticity and strength and used mostly for light weight, high strength structural materials
- Pitch Type Carbon Fiber has high elasticity, heat and electric conductivity and good matching with Lithium ion and therefore used for electromagnetic shield as well as for lithium and fuel battery. It is also used for structural materials with light weight and high strength

## Manufacturing Process of Carbon Fiber (PAN-based) 

- Carbon fiber is made by carbonizing special acrylic fiber (precursor) as a raw material

## Manufacturing Process of Carbon Fiber (Pitch-based) 

- The carbon fiber fabrication from pitch generally consists of the following four steps:
- _Pitch preparation_: It is an adjustment in the molecular weight, viscosity, and crystal orientation for spinning and further heating.
- _Spinning and drawing_: In this stage, pitch is converted into filaments, with some alignment in the crystallites to achieve the directional characteristics.
- _Stabilization_: In this step, some kind of thermosetting to maintain the filament shape during pyrolysis. The stabilization temperature is between 250 and 400 EC.
- _Carbonization_: The carbonization temperature is between 1000-1500 EC.