Thermal Design In Electronics Packaging
Thermal Design in Electronics PackagingPresented byIzuh Obinelo, Ph.D.Director, Center for Airflow and Thermal Technologies Degree Controls Inc 2004Engineered Airflow. Intelligent Cooling.
Agenda Thermal Trends and Challenges in ElectronicsPackaging Effects of Temperature on Reliability ofElectronics Equipment Nature of Thermal Design in Electronics Thermal Design Best Practices Understanding Fans and System Architecture Some Case Studies Degree Controls Inc 2004Engineered Airflow. Intelligent Cooling.
Thermal Challenge in Electronics Industry“Number of devices thatcan be packed in a chipdoubles every 18months”- Dr. Gordon Moore Degree Controls Inc 2004Engineered Airflow. Intelligent Cooling.
Thermal Density: A Comparison10001010.1Rocket Nozzle ThroatVLSI chips 100 ºC10s-100sW/cm2Power Density, W/cm2100Ballistic EntryNuclear BlastReentry from earth orbitRocket Motor CaseSolar Heating100020003000Temperature, Deg KEngineered Airflow. Degree Controls Inc 20044000Intelligent Cooling.
New Challenges. Old Constraints. Watts per unit area in chip and equipment upseveral folds New low power semiconductor technologies outpaced by faster device density growth Heat removal technologies slow to catch up Operating temp ranges of devices have notchanged much in thirty years “Thermal” is the key design constraint Degree Controls Inc 2004Engineered Airflow. Intelligent Cooling.
Agenda Thermal Trends and Challenges in ElectronicsPackaging Effects of Temperature on Reliability ofElectronics Equipment Nature of Thermal Design in Electronics Thermal Design Best Practices Understanding Fans and System Architecture Some Case Studies Degree Controls Inc 2004Engineered Airflow. Intelligent Cooling.
Thermal Design is Critical to Product Reliability The prime cause of failure of electronic equipmentis temperature related Must keep temperatures under control to ensurereliable operation for better reliability Device power dissipations are increasing rapidlywith speed and device density Thermal design is a major limiting factor inperformance. Thermal solutions are nearing applicable physics Great opportunity for Thermal Experts! Degree Controls Inc 2004Engineered Airflow. Intelligent Cooling.
Why is Temperature Detrimental to Reliable Operation of Electronics? Temperature accelerates the following failuremechanisms:( 1 ) Chemical Reactions( 2 ) Diffusion Effects( 3 ) Dielectric Breakdown( 4 ) Ion Movement( 5 ) Electromigration( 6 ) Material Creep( 7 ) Thermal Cycling (Fatigue in solder joints)( 8 ) Board Warpage Degree Controls Inc 2004( 9 ) Performance DriftEngineered Airflow. Intelligent Cooling.
Electronics Device Reliability is Dependent on TemperatureProduct reliability is defined as:R(t) 1-F(t)where:R(t) Reliability,F(t) Probability of failuret TimeIn practice, we determine a failure rate λ (t) experimentally, and canrelate it to R(t) as:R (t ) e t λ ( x ) dx 0 (1)For electronic devices, λ (t) is a constant. Therefore:R ( t ) exp (-λ (t)) Degree Controls Inc 2004(2)Engineered Airflow. Intelligent Cooling.
Electronics Device Reliability is Dependent on Temperature The temperature effect on failure mechanisms such as chemicalreactions is given by:R R0e Ea kT (3) Time to failure is related to temperature as: Ea kT t f t0e(4) Ea is the activation energy; typically 0.5 TO 1.0 eV for Si devicesand 1.5-1.6 eV for GaAs k is Boltzmann constant 1.3802E-23 J/ºK, and T is thetemperature in ºK. Degree Controls Inc 2004Engineered Airflow. Intelligent Cooling.
Life Equivalent to 40 Years in 50300Temperature [C]Relative to 60 C Ambient. Ea 1eV Degree Controls Inc 2004Engineered Airflow. Intelligent Cooling.
The Bathtub Curveλ (t)Failure Rates for Typical ICs with TimetEARLY FAILUREORINFANT MORTALITYSTEADY STATE Degree Controls Inc 2004WEAROUTEngineered Airflow. Intelligent Cooling.
Agenda Thermal Trends and Challenges in ElectronicsPackaging Effects of Temperature on Reliability ofElectronics Equipment The Nature of Thermal Design in Electronics Thermal Design Best Practices Understanding Fans and System Architecture Some Case Studies Degree Controls Inc 2004Engineered Airflow. Intelligent Cooling.
Nature of Thermal Design in Electronics Thermal Design of Electronic Equipment is a MultiFaceted Heat Transfer Subject Invokes all areas of Heat Transfer, such as:– Conduction, Convection and Radiation,– Fluid Flow and Pressure Drop,– Extended Surfaces (Heat Sinks, Fins),– Experimental Techniques,– Empirical Data Analysis,– Numerical or Computational Methods,– Heat Exchanger Design. Degree Controls Inc 2004Engineered Airflow. Intelligent Cooling.
Nature of Thermal Design in Electronics Heat Transfer is an Empirical Science (at Best) Accurate Thermal Prediction within Equipment is a Difficult Task!!!Why?– Complex Geometry, Bends, Obstructions, etc.– Non-Uniform Component Sizes and Layout,– Non-Uniform Board Spacing and Heat Dissipations,– Non-Uniform Flow and Velocity Distributions Within Equipment Accurate thermal modeling is critical Select the right modeling tool for the application There is no substitute for experience Conduct validation tests whenever possible Degree Controls Inc 2004Engineered Airflow. Intelligent Cooling.
The Fundamental Problem Keep junction temperatures of all devices at safe values under all operating conditions Keep board temperature below 105ºCT?qcqkqrbqcbDeviceQ&qkbBoard TjqkbTmax ? Tj qrqcbqkbqrbTbImportant Deployment considerations: Compliance and Safety Ambient temperatures Altitudes Air conditioning failure Solar heat loads Weight and mobility Cost Degree Controls Inc 2004Engineered Airflow. Intelligent Cooling.
Component or Package Thermal Characterization For reliability and performance purposes, equipment designers are ultimatelyinterested in device junction temperatures Heat is dissipated in the device junction, which is conducted through the body of thepackage and the leads to the board and local ambient The ambient is the ultimate heat sink. Heat flows from junction to ambient throughtwo parallel paths junction to package case to ambient (q1), from junction to board (through leads) to ambient (q2) It is often difficult to separate the amount of heat flowing in these two parallel paths.To overcome this difficulty, we define a net thermal resistance from junction toambient as:R ja Degree Controls Inc 2004Tj TaP(5)Engineered Airflow. Intelligent Cooling.
Overall Model for Heat Flow from Junction to Convection Degree Controls Inc 2004Engineered Airflow. Intelligent Cooling.
Thermal Design Hierarchy in ElectronicsCircuit BoardLevelPackage LevelFrame or System LevelChannelBoardShelf{FansThermal Characterizationof Individual DevicesDevice performance asmounted, under anassumed environment Degree Controls Inc 2004Device performance as deployedEngineered Airflow. Intelligent Cooling.
Device-Level Thermal DesignConsiderations: Packaging Design –integrated heatspreaders, multi-coretechnology, etc Thermal vias – use boardground plane as heatsink Heat sink Thermal pads Min airflow required Orientation Degree Controls Inc 2004Engineered Airflow. Intelligent Cooling.
Device-Level Thermal DesignThermal Resistance of 68 I/O PLCC Package:60R ja (ºC /W )5040V 50 ft/min, singlesided30V 400 ft/min,double sided20V 400 ft/min,single sided10012345N Degree Controls Inc 2004Engineered Airflow. Intelligent Cooling.
Device-Level Thermal DesignThermal Vias for Chip on Board Packages:Epoxy Glass BoardXG-2000.4375”Chip1.175”Air FlowCopperHolesChip1/20.3”0.053”0.765”0. 35”0.765”0.4375”oz.Signal0.020” Epoxy C-Stage1 oz.1 oz.1/2oz.Gnd. Plane0.008” Epoxy B-StagePwr. Plane0.020” Epoxy C-StageHeat SinkPlane1.88”Substrate with Copper Holes Degree Controls Inc 2004Cross-Sectional View of PackageEngineered Airflow. Intelligent Cooling.
Device-Level Thermal DesignReduction of IC Thermal Resistance Using Thermal ViasRja (ºC/W)D0 15.6 mils, Di 13 mils4035302520151050Model-No Copper PlatedHolesModel-With CopperPlated HolesExpt. DataExpt. Data1002004006008001000V (ft/min) Degree Controls Inc 2004Engineered Airflow. Intelligent Cooling.
Thermal Design Considerations of PC Board Airflow determination Natural or forced convection Required amount of airflow Optimize Layout minimize shadow effect Locate hotter components in favored areas Heat sinks (Add-on & PCB) Sensors Degree Controls Inc 2004Engineered Airflow. Intelligent Cooling.
Air Cooling - Direct Flow Over Boards Air Cooling is still the most commonly used, Air Flow is provided by fans in forced cooling, or bybuoyancy effects in natural cooling, Amount of flow and velocity developed in an equipmentdepends upon the pressure losses, Typical orders of magnitude of velocity are: Natural Convection (20 - 50 ft/min, 0.1 - 0.25 m/s) Forced Convection in telecom (300 - 500 ft/min, 1.5 - 2.5 m/s) Mainframe Computers (1000 -1500 ft/min, 5 - 8 m/s) FLOW INSIDE EQUIPMENT IS ALWAYS TURBULENT Degree Controls Inc 2004Engineered Airflow. Intelligent Cooling.
System-Level Thermal Design ConsiderationsEquipment design Airflow/thermal design Air intake, exhaust Air mover/filter selection Fan controller design Fan assembly design Degree Controls Inc 2004Engineered Airflow. Intelligent Cooling.
Thermal Issues of Single Rack EquipmentCircuit Bays in Rackswith Single Intake &Exhaust Effect of circuit bays ina Rack Effect of card guides,structures on bays Heat rise through bays Fan assembly design Degree Controls Inc 2004Engineered Airflow. Intelligent Cooling.
Deployment Issues – Room Level Cooling Hot Aisle/Cold Aisle Airflow Distribution tocold aisles Floor layout per heatrack heat dissipation Airflow balancing thru Cooling Efficiencythe room Equipment Reliability Placement of AC units Recirculation of hot air Degree Controls Inc 2004Engineered Airflow. Intelligent Cooling.
Agenda Thermal Trends and Challenges inElectronics Packaging Thermal Design and Reliability ofElectronics Equipment Nature of Thermal Design in Electronics Thermal Design Best Practices Understanding Fans and System Architecture Case Studies Degree Controls Inc 2004Engineered Airflow. Intelligent Cooling.
Stages of Thermal DesignElectrical and Software DesignExpected airflowrates andtemperature riseStage 1PrototypingThermalAnalysisDesignStart- Overall coolingrequirements- Initial coolingsystemspecificationComponentdetails andboardlayoutModifiedboardlayoutStage 2Detailed ThermalDesign- Device temperatures- Detailed cooling profiles- Heatsink design &selection- Probe design envelope:failure scenarios,elevated temperatures,elevationValidate finalcomponentplacements.Finalizeheatsinksand TIMsValidatecomponent tempsat: Startup, fanfailure, high temp,filter blockageFine tunethermalcontrolalgorithm.Finalize setpoints.Stage 3Initial DVTStage 4Final Thermal DVT- Build & testphysical mockup- Validatethermal model- Temperature & Flowmeasurements- Survivability underfailure scenarios- Thermal controllerspeed tuning- Burn-in- Agency pre-qual testsConfigurationinstructions.Performance infoStage 5DeploymentLevel Analysis- Temperature &Flowmeasurements- Proximity checks- Vent blockagechecks- Multipleconfigurations(ProductConcept)Overall chassissize, plenums,ventsCADFilesVent %openares, Filterselection, EMImitigationFinalize ventsand grilles,filter, fanplacements,plenum heights,surface finishesFinalizeHardwaredesign:Chassis,Fan tray,ControllerValidateacoustics andoperation atambient temp,humidity,altitudeDeploymentinstructionsUsage instructionsService instructionsPhysical/Mechanical Design Degree Controls Inc 2004Engineered Airflow. Intelligent Cooling.
Concurrent Thermal Design Faster time to market Simulate Directly on DesignGeometry Migrate changes quickly tomechanical and electrical designs Avoid Costly Redesigns design must be right first timearound Design to IndustryStandards NEBS, CSA, CE, etc Degree Controls Inc 2004Engineered Airflow. Intelligent Cooling.
Design-Based Thermal Simulation ApproachCreate ModelGeometry Build 3D CFD-CAD Model from Design CAD Models Discretize CFD CAD Model Tetrahedral elements for air and solid objectsMesh ModelGeometryCFD Model Triangular elements on all convecting surfaces Impose initial conditions, boundary conditions and fancurves, rotational motion if applicable Initial conditions are ambient conditions everywhere Boundary conditions are heat loads, ambient (room) conditions Rotational motion is speed of rotation of the rotor in rpmSolve CFD model Create control volumes Solve for CFD quantities @ integration pointsF AX B Post-Process Results (temperatures, velocities,pressures, heat transfer coefficients, etc)T,P,V,h Degree Controls Inc 2004Engineered Airflow. Intelligent Cooling.
Thermal Design Starting PointsSpecify: Cooling Method (Natural/Forced Convection) Architecture (Push/Pull/Push-Pull) Ambient Temperature Range Quality of Air (Dust, Humidity) Intake and Exhaust Paths Noise Levels Power Budget Servicing Module Repair Time Degree Controls Inc 2004Engineered Airflow. Intelligent Cooling.
Experience is a Premium Develop Simple Engineering Rules to EvaluateEquipment Designs Have an Idea of Answers BeforeExperimentation Implement Recovery from Single-point Failures Degree Controls Inc 2004Engineered Airflow. Intelligent Cooling.
Agenda Thermal Trends and Challenges inElectronics Packaging Effects of Temperature on Reliabilityof Electronics Equipment Understanding Fans Thermal Design Methodologies Data Rooms: The next frontier Degree Controls Inc 2004Engineered Airflow. Intelligent Cooling.
Fan Types: Tube-axial Fans Inexpensive More suppliers Pressure capabilities arelimited in high impedancesystems. Ideal for low impedanceapplications. Degree Controls Inc 2004Engineered Airflow. Intelligent Cooling.
Fan Types: Impellers (Radial) High impedance high flow Ideal for Pull systems due tonatural 90 turn. Pressure capabilities are verygood. Fan spacing is limited due toflow path. Degree Controls Inc 2004Engineered Airflow. Intelligent Cooling.
Fan Performance and System ResistanceI,QRV,pAirflow SystemElectrical SystemBatteryPerformancecurveFan PerformancecurveResistancecurveVoltageVSystem curveStaticpressurepCurrentI Degree Controls Inc 2004AirflowQEngineered Airflow. Intelligent Cooling.
Determining Pressure-Flow Curve of a FanFan Under Test P, PressureQ PQ, AirflowΦDPQ Change P from 0 to max (zero flow) by adjusting tunnel flow Measure PQ and calculate Q, gross airflow Plot Q- P curve Degree Controls Inc 2004Engineered Airflow. Intelligent Cooling.
Determining System Resistance Curve of EquipmentEquipment Under Test P, PressureQ PPQQ, Airflow Change P from 0 to max (zero flow) by adjusting tunnel flow Measure PQ and calculate Q, gross airflow Plot Q- P curve Degree Controls Inc 2004Engineered Airflow. Intelligent Cooling.
Selection of the right fan and the Operating PointOperating Point: A Low Airflow Inefficient Performance High Noise LevelSystemcurvesMultiple operating pointsStaticpressureAOperating Point: B High Airflow Efficient Performance Low Noise LevelCOperating Point: CBFan Performance curveAirflow Degree Controls Inc 2004 Multiple Operating points for samepressure Fan speed hunts between the operatingpoints Inefficient Performance High cyclic Noise Level Significant reduced fan lifeEngineered Airflow. Intelligent Cooling.
Smart Design Offer Major Gains Can we simply increase airflow as powerincreases? What are the cost implications? Here is a quick summary. Degree Controls Inc 2004Engineered Airflow. Intelligent Cooling.
FAN LAWSFan performance is measured in terms ofPressure P ,volume flow rate (Q), and power absorbed(W)These are dependent upon a number of factors( 1 ) type of fan (tube axial, vane axial, blower)( 2 ) operating point on the fan curve, DP vs Q( 3 ) size of fan (diameter D)( 4 ) speed of rotation (N, rpm)( 5 ) density of gas or air (ρ) Degree Controls Inc 2004Engineered Airflow. Intelligent Cooling.
FAN LAWSBy considering a point of operation on fan curveIt is possible to derive some simple scaling lawsBetween P , Q, W, D, N, and ρ for a fanSuch asQ F1 (D, N) P F2 (D, N, ρ )W F3 (D, N, ρ )These Functional Relationships Are Called "FAN LAWS" Degree Controls Inc 2004Engineered Airflow. Intelligent Cooling.
AirflowFrom dimensional analysis we obtain FAN LAWS as(1)Q α D3 NFrom ( 1 ), Q is independent of density. thereforefan at sea level or say 2000m. has same Q capacity.But Fan Mass Flow Rate ( ρQ ) varies with altitude.Also from (1), Q varies linearly with N Degree Controls Inc 2004Engineered Airflow. Intelligent Cooling.
Pressure and Power( 2 ) Differential Pressure P α D2 N2 ρ( 3 ) Pumping Power,W α D5 N3 ρFrom (1), (2), and (3),W Q . P(Ignoring all electrical efficiencies) Degree Controls Inc 2004Engineered Airflow. Intelligent Cooling.
Sound PressureSound Power Level S has the functional relationship(4)Sα Q DP2,α( D3 N ) ( D2 N2 q )2αD7 N5 ρ2For a given D and ρ,S α N5Fan Noise Is Very Strongly Dependent on Speed N Degree Controls Inc 2004Engineered Airflow. Intelligent Cooling.
Design ImplicationsLet us understand the engineering implications ofthese 4 fan laws for Q, P, W and SFor a given fan we want to increase Q by 25 %What are the implications?From (1), To Increase Q by 25%, increase N by25% Degree Controls Inc 2004Engineered Airflow. Intelligent Cooling.
Design ImplicationsFrom (3), Fan Pumping Power W increases by1.253 1.95,that is an increase of 95% in fan powerFrom (4), fan sound power level S increase is1.255 3.05,that is an increase of 305% in noise power S Degree Controls Inc 2004Engineered Airflow. Intelligent Cooling.
Design ImplicationsFan Sound Law (4) can be expressed in dB form as change in sound powerlevel from speed N1 to N2 as dB dB(N2)-db(N1) 10 log(N2/N1)5 50 log(1.25) 4.85(5 dB difference in sound level is noticeable) Degree Controls Inc 2004Engineered Airflow. Intelligent Cooling.
A ComparisonResults are tabulated for N2 1.25 N1 and N2 2 N1N2/N1Q2/Q1 P2/ P1W2/W1dB211.251.251.563.054.85224815 Degree Controls Inc 2004Engineered Airflow. Intelligent Cooling.
Nutshell Heat Transfer Coefficient h α V0.7. So doubling N increasesh by 62% To remove 62% more heat, airflow should be doubledQ2 2*Q1 ORN2 2*N1 Doubling flow causes P to increase by a factor of 4( P α V2) Power required to double airflow is W2 8* W1 Sound level increases by 15dB Fan bearing life deteriorates rapidly with higher speed N.Therefore fan life deteriorates drastically. Degree Controls Inc 2004Engineered Airflow. Intelligent Cooling.
Nutshell Increasing flow rate beyond a certain value isnot worthwhile This is “Murphy's law" for electronic cooling Optimize your design (heat removed/pumpingpower ) “Smart Thermal Engineering” This observation is true for cooling devices,boards, chassis or data rooms. Degree Controls Inc 2004Engineered Airflow. Intelligent Cooling.
Cost Implications Expensive, High performance fan Larger Power Supply Lower Life Acoustic and electrical noise filtering Degree Controls Inc 2004Engineered Airflow. Intelligent Cooling.
Thermal Design Methodologies Design Process Architectures Failure detection and recovery Designing for Reliability Design validation- Testing Degree Controls Inc 2004Engineered Airflow. Intelligent Cooling.
Fan Placement - Push vs. Pull SystemAirflowDistributionPush System Degree Controls Inc 2004Pull SystemEngineered Airflow. Intelligent Cooling.
System-Level Thermal ArchitecturePush DesignPros: Pressurized system - clean air Low fan operating temperatureExhaustCons: Filter often to
Electronics Packaging Thermal Design and Reliability of Electronics Equipment Nature of Thermal Design in Electronics Thermal Design Best Practices Understanding Fans and System Architecture Case Studies Degree Controls Inc 2004 Engineered Airflow. Intelligent Cooling.
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interconnection, thermal management, and mechanical and environmental protection. Each packaging level reflects a trade-off among many interrelated factors including design requirements, economics, and manufacturing infrastructure. (Keywords: Electronic components, Electronic packaging, Packaging design, Packaging levels.)
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