BTeV Pixel Substrate C. M. Lei November 2001

Design Spec. Exposed to >10 Mrad Radiation Exposed to Operational Temp about –15C Under Ultra-high Vacuum, 10E-4 torr or better Serve as a Dimensionally Stable Support Serve as a Heat Sink to remove heat 60W (0.5W/cm^2)

Material Spec. Rad-Hardness and Low Rad Length Low Out-gassing Rate Light and Stiff High Thermal k and Low cte

Design Approach Address Cooling Needs First Heat Removed Basically by Conduction to Coolant: Q = k*A* T/ L Maximize k*A while Keeping Thickness L Small

Design Types Cooling Tubes Array with Added Substrate (Fuzzy C Design) Cooling Chamber as Substrate (Beryllium Design)

Cooling Tubes Array with Added Substrate Need Manifolds and many Joints Need to build up Substrate on Array Allow Porous Substrate – Low Rad L Seamless Tubing Array Generate a Temp Drop across the Array/Substrate Interface Effective Heat Transfer Area limited

Cooling Chamber as Substrate Need to Machine Integral Cooling Channels Need to make a Large-Surface Quality Joint at the Interface Huge Area for Heat Transfer Wall = Substrate, Min. Thickness Allow Smaller Temp Drop due to 1 less Joint Impedance

Material Choices

Fuzzy Carbon Design All Carbon Heat Exchanger - Non-permeable Leak-tight Glassy Carbon Tubing, Manifold and Joints Tubing Flattened in Cooling Area and Bonded together to form a Stiffened Array Radial high k Carbon fibers bonded to Array with Intimate Carbon Joint Pixel Sensors to be supported directly by fuzzy carbon fibers Leak-tight Carbon Joints Toughened by Resin mixed with Carbon Nanotubes (Preferred, Regular Epoxy may be allowed to use)

Radial Fintubing Array Top View Bottom View

Ovalized Tubing Array Ovalized C tubing precursor fuses together for greater stiffness Monolayer of C fiber applied to ovalized tube array

Carbon Coupon Toughening and fuzzy C interface not illustrated here

Coupon Test Article Al Manifold With epoxy joints C Manifold With C joints

Problems Before Tubing and Joint Broken Many fibers not in contact with Tubing Small diameter thin wall tubing Tubing Array used as the sole Support Brittle carbonized joint between tubing and manifold (just good for sealing purpose)

Prospective Solutions Use larger diameter, thicker wall tubing, and fused together to form a solid cooling array Use C superstructures next to cooling array and connect them to manifolds to form a rectangular back-frame support Toughen the manifold/tubing joints with carbonized resin or regular epoxy Radial C fibers are sure in contact with tubing by forming a solid cooling array

Be Substrate Design 4X 0.5-mm-Deep Channels Cooling Strips along the Channels Overall Thickness mm Ave. Rad L per Plane = 0.33%

Be Substrate – Bottom Plate

Be Substrate – Top Plate

Be Substrate – Assembly

Flow Test on Be 960 cc/min

Loading on Bond Area Coolant Contact Area = 8.9 in^2 For P = 80 psi, F = 710 lbf Bonding Area = 5.8 in^2 Tensile Stress in Bond = 122 psi If Peeling occurs, (assume all forces acting on 1 line) PIW =150

Choices of Structural Adhesives

FEA on Be Substrate Heat Load from ROC =.5 W/cm^2 Heat Load from Sensor =.025 W/cm^2 Constant Coolant Temp = -15C Coolant Pressure = 40 psi Convective film Coef. = 2000 W/m^2*C Radiation Effect Ignored (< 1%) Surrounding Temp = 20C

Temp Profile 3.8C Coolant Temp = -15C

Temp Profile Coolant Temp = -15C 3.8C

Temp Profile

Displacement UY UY = 0 at 4 corners.071

Displacement UX UX = 0 this side.018

Displacement UZ.025 mm UZ = 0 this side

Resultant Stresses (16,710 psi) Be Sy = 240 MPa

Resultant Stresses in Epoxy Layers (5,550 psi) Stresses can be lowered significantly If epoxy with lower E is used. E = 1 Msi

Resultant Stresses in ROC (5,440 psi) Sy = 120 MPa

Resultant Stresses in Sensor (5,470 psi) Sy = 120 MPa

Temp Profile of 8-chip Module Coolant Temp = -15C In this model, bump bonds between ROC & sensor are added. Kapton HDI cable with epoxy are also added. Results of temperatures, displacements and stresses Are somewhat similar and less because of smaller size of model.

Temp Profile on ROC

Resultant Stresses in HDI Cable (290 psi) Tensile stress of Kapton = 24,000 psi

Resultant Stresses in Bump Bonds Bump bonds (0.01mm DIA, 0.01mm high) were modeled with Beam Elements Min Principle Stress = -104 Mpa (15,000 psi) Max Principle Stress = +189 Mpa (27,400 psi) Tensile Strength of Indium = 1.6 Mpa ~13.7 Mpa (?) Stresses can be reduced significantly if 0.5mm wide epoxy can be glued around the ROC Reinforced Min Principle Stress = -71 Mpa (10,300 psi) Reinforced Max Principle Stress = +44 Mpa (6,380 psi)

Resultant Stresses in Reinforced Epoxy (4.600 psi) (0.5mm wide epoxy around ROC perimeter)

FEA Conclusions on Be Substrate For h = 2000, Temperature Distribution OK For T = 35C, Thermal Displacements OK Stresses on Epoxy is High Stresses on Bump Bond is not Acceptable Displacements and Stresses can be reduced if Smaller T allowed

Choices of Thermal Conductive Epoxy

Thermal Cycle Test After 5 cycles between –15C and 20C, all 3 epoxies stay OK.

Other Tubing-Array Designs

Rad L % of Designs

Future Plans Run Thermal Test and verify effective h with cooling-strip effect included Try to lower coolant temp to –10C or so Evaluate and Select Epoxies Do Thermal Cyclic Test on Si Dummies with Bump-Bond Do Bump-bonds Testing Works on other Designs