Pixel upgrade test structure: CO 2 cooling test results and simulations Nick Lumb IPN-Lyon MEC Meeting, 10/02/2010

Pixel upgrade ‘facet’ test structure Add heat load (foils) at extremities Circulate cold CO 2 Measure delta T (coolant, sensor) 3W per sensor Temp. range -15 → -30C Layer 1 prototype Dummy facet

Cross section through test structure Silicon area: 60 x 18 mm Heating foils exactly cover this area Heat input to max. power = 25 W/m

Temp. Sensor positions Temp. Sensors: Analog Devices AD590 Calibrated using thermal bath to +/-0.2°C Attached to wafers and pipes using thermal epoxy, 0.76 W/m.K

Heaters ON 2 x 3W Heaters ON 2 x 3W Decrease power 2 x 1.5W Heaters ON 2 x 3W Decrease power 2 x 1.5W Run no. 1 (Preliminary run) Run no. 2 (Better insulation) Run no. 3 (Copper plates) Plate mounted on CF On wafer On pipes below wafer CO 2 flow rate: 1.0 g/s; freezer temp.: -20C Increase CO 2 flow 1.5 g/s Plate mounted on pipes 20°C 8°C

Run no. 3 - copper plates Thickness 3mm Square channels filled with conductive paste No serious attempt at good thermal contact One plate mounted as shown Second plate mounted on CF frame with conductive paste, 0.77 W/m.K

Conclusions: experimental results  Test structure as-is: ΔT pipe to Si sensor ~20°C  Replace Si + CF + epoxy with copper block + thermal paste → ΔT ~8 °C  Agreed to re-visit simulations to investigate problem

Simulation studies  FloEFD V build 1160  Add-on to CATIA V5.19

EFD simulation: solids modelled (1) Pipe Si wafer CF support Glue joint

EFD simulation: solids modelled (2) Heater foil + adhesive

Solids properties ItemMaterialThicknessThermal conductivity (W/m.K) PipesStainless steel50μEFD library (temp. dependent; Glue jointsAraldite 2011Variable; min. 20μ 0.22 CF supportT300J200μX: 10.0; Y: 10.0; Z: 0.9 DetectorSilicon285μEFD library (temp. dependent; Heating foil adhesive Acrylic glue50μ0.50 Heating foilKapton300μ0.52

Simulation: additional details  Volume heat source: heater foil solid, 3W  Fixed temperature of 253.2K on pipe inner walls  Refined local meshes for: pipes, glue joints, CF support

EFD simulation: Results (1) (nominal Thermal Conductivity values)

EFD simulation: Results (2) (nominal Thermal Conductivity values)

Overall ΔT vs Thermal Conductivity of component materials (simulation results)

Simulation: conclusions  ΔT heating foil → pipe = 11.3°C Compare 20°C experimental value  Very sensitive to epoxy conductivity ΔT = 17.8°C for K epoxy = 0.1 W/m.K instead of 0.22 W/m.K  Also quite sensitive to perpendicular component of CF conductivity  CF in-plane conductivity less important  Modelling of heater + adhesive adds ~1°C of ΔT

Remarks  Simulation ignores several real-life imperfections: Contact heating foils with Si Contact temp. sensors Contact Si with CF …  Best ΔT we can hope for with this design seems to be ~5°C  Assumes conductive epoxy E.g. H20E EPO-TEK → K = 2.0 W/m.K  Can we improve on K perp for CF?  Can we improve the overall design? E.g. Pipes embedded in CF

Re-circulating system

Next steps  Test new pixel structure(s) with present (‘blow’) system?  Build and debug re-circulating system Design work complete Rack construction already started  Start to look at new support / cooling structures for ‘strip’ TK