Cooligy. The Heat Problem. Why Keep CPUs Cool? Active Micro-Channel Cooling. Peak Power Density (Watts/cm 2 ) Total Power (Watts)

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1 Active MicroChannel Cooling The Heat Problem Total Power (Watts) RISC Pentium Pentium 4 Pentium III Next Generation Why Keep CPUs Cool? Greater Performance Better Reliability 0 Peak Power Density (Watts/cm 2 ) 486 RISC Pentium Next Generation Pentium 4 Pentium III Source: Industry, 9/4/

2 Microprocessor Thermal Requirements X86 Case to Ambient Aircooling limit Current Case to Ambient Source: 9/4/ Microprocessor Thermal Management Microprocessor thermal management challenges Very high average and peak power densities Q _average > 150 W/cm^2 Q _peak > W/cm^2 Thermal management requirement outpaces aircooling technologies Genossar, D., and Shamir, N., 2003, Intel Pentium M Processor Power Estimation, Budgeting, Optimization, and Validation, Intel Technology Journal, Vol. 7(2), pp Electrokinetic microchannel cooling system advantages Orders of magnitude higher effective heat transfer coefficient compared with aircooled heatsinks and liquidcooled coldplates Microchannels can be readily implemented for hotspot cooling Very efficient liquidair heat exchanger 9/4/

3 Keeping Cool CPU Power Natural Convection Active Fan Sink Passive Fluid Heat Pipe 9/4/ Microchannel Cooling System Radiator Electrokinetic Pump Microchannel Heat Collector CPU 9/4/

4 MicroChannels Provide Highest Performance Heat travels a short distance into the fluid before being carried away Pumped Fluid MicroChannel Heat Collector Thermal Grease CPU CPU Hotspot Cooling Distance ~1 mm micro micro Heat Transfer Efficiency macro Pressure Differential macro Channel Width Channel Width ~Width of a hair 9/4/ ElectroKinetic Pump No Moving Parts Porous Glass Disk Electric field drives fluid through porous glass disk High pressure, high flow rate Silent operation Reliable no moving parts Billions of pathways through glass disk Ion drag moves water near surface of glass water SiO 2 H 2 O Positive voltage glass hydrogen ion oxygen silicon Negative voltage 9/4/

5 Electrokinetic Fluid Flow The fixed surface charge creates a diffuse double layer region of net positive charge near the surface. Applied electric field acts on charges and causes fluid to flow. E ζ potential Water Velocity Profile E Hydrogen ion Fixed negative charge of oxygen 9/4/ System Thermal Design Performance Target Design Electrokinetic pump model System model Fan model Microchannel heat exchanger compact model Boundary conditions Liquidair heat exchanger compact model Detailed component model (CFD) Microchannel geometry Proprietary manifold Maximize UA on liquid and air passage Optimized flow arrangement ensures heat transfer efficiency 9/4/

6 Thermal Die Numerical and Experimental Results Simulation Experiment TDP [W] Q _avg [W/cm^2] Q _peak [W/cm^2] Experimental setup Ta [degc] Tj = 74.5 degc V_dot_air [CFM] V_dot_l [ml/min] 300 ~280 2 mm Rja [degc/w] Junction temperature distribution 150W, 360W/cm 2, 300ml/min@25degC water 9/4/ Pentium 4 Model Parameters Ambient temperature, C 40 CPU die size, cm 2 1 CPU power, W Die thickness, mm Spreader size, mm Integrated heat spreader thickness, mm Integrated heat spreader material Hot spot size, mm 2 Power density at hot spot, W/ cm 2 No. of hot spots Rejecter size (mm) Airflow through rejecter, cfm x Cu x 50 x /4/

7 Simulation Results Liq. exit Liq. in Component Silicon Die TIM1 Resistance C/W TIM2 Micro channel casefluidrejecterambient Total Resistance, R ja Airflow 9/4/ Passive Cooling: Fan Heat Sink Average power cooling Heat must spread up to reach cooling air Fan heat sink is many times larger than the CPU 120 Watt CPU Hot spot in center 9/4/

8 Active MicroChannel Cooling Efficiently cools hot spot Active microchannelcooling area is 710 times the area of the die Cooling fluid brought directly to hottest areas on die 120 Watt CPU Hot spot in center 9/4/ Example: RISC Workstation Power Scaling Power Mechanical 90 4 Heat pipe Junction Temperature Rejecter size Liquid flow rate ml/m Airflow per CPU, cfm Hot spot Flux, W/cm 2 120x90x Mechanical 120x90x Fluid Cooling 4Heat pipe 120x90x90 43 Higher total power per CPU Lower fan speed 9/4/

9 Active Fluid Air Flow Advantage Power Small form factor fluid Small form factor 3heat pipe Airflow, cfm Small form factor radiator Ambient temperature = 38C 9/4/ Target Applications Workstation 1U Server Small Form Factor 9/4/