nus cht course
TRANSCRIPT
Slide 1
ME6204 Convective Heat Transfer
Thermal Management of Electronic Components
Mujumdar A S and Ravi K
January 2006
Slide 2
Introduction
Basic Thermal Problems in IC Packages and Electronic Systems
Heat Transfer path in IC packages
Thermal Definitions and JEDEC standards
Basic Approaches for IC package Thermal Performance Characterization
Analytical Approach
Modeling approach*
Experimental Approach*
Thermal performance
- Package level with examples
- Heat sink selection with examples
Summary
Outline of TopicsOutline of Topics
* Covered basic details
Slide 3
Needs of thermal management for electronic Needs of thermal management for electronic packages and systemspackages and systems
Basic concepts, definition and industrial Basic concepts, definition and industrial approaches for thermal characterization of approaches for thermal characterization of electronic packageselectronic packages
To understand the package thermal performance To understand the package thermal performance with different external cooling arrangementswith different external cooling arrangements
IntroductionIntroduction
Slide 4
Reynell, M. 1990
Source: U.S. Air Force Avionics Integrity Program
Major Causes of Electronic FailuresMajor Causes of Electronic Failures
Slide 5
Control of TJ = Goal of electronic coolingHigher TJ yields shorter device lifeHigher TJ poor image capture
Jc/TeLife
Lifespan Vs Junction TemperatureLifespan Vs Junction Temperature
Slide 6
Heat Fluxes For Various EventsHeat Fluxes For Various Events
Chu, Simons, et.al 1999
Heat Fluxes for Various ElementsHeat Fluxes for Various Elements
Slide 7
Increasing module and device heat fluxes
Declining thermal design-margins
Trends in Electronic CoolingTrends in Electronic Cooling
Slide 8
Packaging Controls
Size Weight Performance Reliability Cost
What is Packaging?What is Packaging?
Source: IEEE/CPMT
Slide 9
Today s electronics product are very complicated systems containing many thin layers, narrow conducting wires, tiny solder joints etc.
Because of the fine features and large number of parts involved in each design the probability of system failure is high unless all the design considerations are taken into account.
This presentation covers only some aspects of design, production, testing, and packaging of electronic products issues based on package structural considerations.
Why care about Packaging?Why care about Packaging?
Slide 10
To keep the maximum junction temperature To keep the maximum junction temperature within the specified limit (within the specified limit (TjTj < 125< 125 C)C)
Effective/Economic heat removal out of electronic Effective/Economic heat removal out of electronic systemssystems
Thermal Issues in ElectronicsThermal Issues in Electronics
Slide 11
???
Various Electronic PackagesVarious Electronic Packages
Source: www.electronics-cooling.com
Slide 12
Package Thermal PerformancePackage Thermal Performance
Source: www.electronics-cooling.com
Slide 13
Package size decrease Package size decrease ------> Hot> HotDie size decrease Die size decrease ------> Hot> HotSystem complexity increase System complexity increase -- HotHotClock speed in crease Clock speed in crease -- HotHotLower power process, lower Lower power process, lower volatgevolatgeI/O increaseI/O increase
Thermal Trends in Electronic Thermal Trends in Electronic PackagesPackages
Slide 14
Both are critical for thermal design of a system Both are critical for thermal design of a system and componentand component
Thermal characterizationThermal characterizationInvolves the determination of thermal fields Involves the determination of thermal fields
and its gradients (spatial and temporal), and its gradients (spatial and temporal), representative thermal parameters throughout representative thermal parameters throughout the system and component the system and component
Thermal managementThermal managementInvolves heat removal strategies from the Involves heat removal strategies from the
electronic package, PC board and systemelectronic package, PC board and system
Thermal Management/CharacterizationThermal Management/Characterization
Slide 15
Methodology levelsMethodology levelsPackagePackagePCBPCBSystemSystem
Analysis and Technical skillsAnalysis and Technical skillsHeat transfer Heat transfer
Conduction, Convection and RadiationConduction, Convection and RadiationComputational Fluid DynamicsComputational Fluid DynamicsNumerical Numerical modellingmodellingExperimentExperiment
Thermal Analysis for ElectronicsThermal Analysis for Electronics
Slide 16
ConductionConductionheat transfer occur within the solid heat transfer occur within the solid
Convection Convection -- heat transfer by external fluid or gas that heat transfer by external fluid or gas that surround the surfacesurround the surface
Natural ConvectionNatural Convectionheat transfer based on the principle that hot air risesheat transfer based on the principle that hot air rises
Forced ConvectionForced Convectionheat transfer by forced air blown across the surface heat transfer by forced air blown across the surface
RadiationRadiationheat transfer calculation based on energy released by heat transfer calculation based on energy released by
radiation.radiation.
Heat Transfer Mechanism in Electronic Heat Transfer Mechanism in Electronic packagespackages
Slide 17
Source: www.electronics-cooling.com
Major heat pathsPackage top to AirPackage Bottom to boardPackage leads to board
Heat Transfer in Electronic packagesHeat Transfer in Electronic packages
Slide 18
Source: www.electronics-cooling.com
Heat Transfer in Electronic packagesHeat Transfer in Electronic packages
Slide 19Source: www.electronics-cooling.com
- Moore s law: The number of transistors in an IC doubles every 18 months- Need for new cooling techniques
- Driven by increases in power dissipation -A heat flux of 100 W/cm2 at a temperature difference of 50 K
- Requires an effective heat transfer coefficient of 20,000 W/m2K
Packaging Technology TrendsPackaging Technology Trends
Slide 20
Comparison of Heat FluxesComparison of Heat Fluxes
Slide 21
Source: www.electronics-cooling.com
- Need for liquid cooling in the future of thermal management
Various Cooling in ElectronicsVarious Cooling in Electronics
Slide 22
Source: www.electronics-cooling.com
IC package with thermal conduction path to heat sink via TIMsFor high-power applications, TIM resistance becomes an important issueHigher thermal conductivities, BLT and CTEs
Conduction and Heat Spreading Conduction and Heat Spreading Cooling Cooling
Slide 23
Source: www.electronics-cooling.com
- Effect of thickness on heat spreading for various heat source areas,- Material thermal conductivities and - Heat transfer coefficients
Heat Spreading Results Heat Spreading Results
Slide 24
Source: www.electronics-cooling.com
- Fan Cooling limits:- Std Fans with accepted noise level max. heat transfer co-efficient: 150 W/m2K- Heat flux of 1 W/cm2 with 60 C temperature difference
- Macro jet impingement- HTC: 900 W/m2K
- Non std fans/dedicated heat sinks for CPU cooling- Heat flux of 50 W/cm2- 10x better than 15 years ago
- Piezo Fans - Air coooling enhancement - Low power, small and relatively low noise fan used- 100% enhancement over natural convection heat transfer- Research: Perdue, " HeatTransfer Eng., Vol. 25, 2004, pp. 4-14 Synthetic Jet impingement
- Synthetic Jet Cooling
- Nanolightning
High performance Cooling in High performance Cooling in Electronics Electronics
Slide 25
Source: www.electronics-cooling.com
Synthetic Jet ImpingementSynthetic Jet Impingement
Slide 26
NanolightningNanolightning
Source: www.electronics-cooling.com
- New approach to increasing the heat transfer coefficient called 'nanolightning , from Purdue . - Based on 'micro-scale ion-driven airflow' using very high electric fields created by nanotubes. - The ionized air molecules are moved by another electric field, thereby inducing secondary airflow [9]. - Cooling a heat flux level of 40 W/cm2 has been reported. - Technology is being commercialized through a start-up company (Thorrn).
Slide 27
Liquid coolingLiquid cooling
Source: www.electronics-cooling.com
- Liquid Cooling ( upto 2000 Kw/cm2 is possible), - Experimental value reported upto 200 kw/cm2- Micro coolers can handle upto 1 kw/cm2
- Direct cooling- Immersion cooling- Jet impingement
- Indirect cooling- Heat pipe - Cold plate
- Micro channels and Mini channels- Electrodynamic and electrowetting cooling- Liquid metal cooling- Thermo electric cooling- Thermionic and Thermotunneling cooling- Super lattice and Heterestructure cooling- Phase change materials and heat accumaltors
Slide 28
Heat Pipe: High Performance Cooling in ElectronicsHeat Pipe: High Performance Cooling in Electronics
Source: www.electronics-cooling.com
Indirect passive coolingEffective thermal conductivity range: 50 kw/mK to 200 kW/mKPerformance of heat pipe: 10 W/cm2 to 300 W/cm2
Simple water heat pipe heatt transfer capacity is 100 W/cm2 (Average):
Picture: Note book applications
Looped heat pipeSeparate liquid and vapor flow pathHeat flux upto 625 W/cm2
Slide 29
Different Advanced coolingDifferent Advanced cooling
Source: www.electronics-cooling.com
Spray Cooling
Immersion Cooling
Mutiple Jet impingement Cooling
Slide 30
Thermal ConsiderationsThermal Considerations
Slide 31
In general the package therm al perform ance is characterizedbased on the following five different basic therm alparam eters based on heat dissipation requirem ents.
Therm al Resistance : JA, JC & JB
Therm al Characterization param eter : JB
& JT
What are different Thermal numbers?What are different Thermal numbers?
Slide 32
Thermal parameter - Notation
RJA or JA or JMA or JX or JR - Thermal Resistance:Junction to ambient (in still air or moving air)
RJC or JC - Thermal resistance: Junction to caseRJB or JB - Thermal Resistance: Junction to board
JT - Thermal characterization parameter: Junction to top center of the package top
JB - Thermal characterization parameter: Junction to the board
Where,R - Reference point X - Measured locationA - Ambient conditionsMA - Moving air
Slide 33
In general the package therm al perform ance is characterizedbased on the following five different basic therm alparam eters based on heat dissipation requirem ents.
Therm al Resistance : JA, JC & JB
Therm al Characterization param eter : JB
& JT
What are different thermal numbers?What are different thermal numbers?
Slide 34
JA - Junction-to-Ambient Thermal ResistanceDefinition
What does it mean?
- It reflects how well heat flows easily from junction to ambient via all paths.- Relevant for packages used without external heat sinks.
Use of Junction to Ambient Thermal Resistance?
- Used to compare thermal performance of packages for selection of packagetype, materials and package supplier.
- If two packages with same JA
should perform equally well in an actualapplication.
- A package with a lower value of JA
should perform better in an applicationthan one with a higher value. Lower is good.
- Used to calculate package power capability. If package JA is knownpackage power capability can be calculated for a particular application.
- Used to calculate die temperature when environment is similar to the testenvironment. (Formula should be used with great caution).
How to measure this value?
- Mount package on standard JEDEC thermal test board- Put package in standard test environment Wind tunnel or JEDEC enclosure- Apply known amount of power- Measure temperature of chip TJUNCTION and temperature of air TAMBIENT
-
Perform calculation using definition
POWER
TTR AMBINETJUNTION
JA
Slide 35
Junction to Ambient Thermal ResistanceJunction to Ambient Thermal ResistanceNatural ConvectionNatural Convection
Heat Flow In Still AirHeat Flow In Still AirJEDEC Still air boxJEDEC Still air box
Thermal Measurement Thermal Measurement
P
TTR AJ
JA
DefinitionDefinition
Slide 36
Junction to Ambient Thermal ResistanceForced Convection
Heat Flow In Forced AirHeat Flow In Forced Air
P
TTR AJ
JA
DefinitionDefinition
Wind TunnelWind Tunnel
Thermal MeasurementThermal Measurement
TA
TJ
Die
Package
Slide 37
Definition
What it means?
- It measures ease of heat flow between the die and the surface of the package- Relevant for packages used with external heat sinks
Application of Junction to case thermal resistance?
- It applies only to situations in which all or nearly all of heat is flowing out oftop or bottom of package.
- Low value means that heat will flow easily into external heat sink.- It is not a useful thermal characteristics to predict junction temperature
How to measure this value?
- Mount package on standard JEDEC thermal test board or socket- Put package in contact with water-cooled cold plate
- Insulate package from air- Force all heat to flow to cold plate though package surface
- Apply known amount of power- Measure temperature of chip TJUNCTION and temperature of package surface
(case) TCASE.
-
Perform calculation using definition
POWER
TTR CASEJUNTION
JC
JC
Junction-to-Case Thermal Resistance
Slide 38
Measurement of RJC
P
TTR CJ
JC
Thermal MeasurementThermal Measurement
DefinitionDefinition
Heat flow with heat sinkHeat flow with heat sink
Slide 39
Definition
What it means?
- It provides overall thermal resistance between die and the PCB.- Defined to be the difference in the junction temperature and the PCB
temperature closer to the package at center.
How to measure this value?
- Mount package on standard JEDEC thermal test board- Mount thermocouple on board at edge of the package- Applies only for 2S2P test board.- Measure temperature of die TJUNCTION and temperature of the board near to
the package at center location.- Perform calculation using definition.
POWER
TT BOARDJUNTIONJBR
JB
Thermal Resistance: Junction-to-Board
Slide 40
P
TTR BJ
JB
DefinitionDefinition
Measurement FixtureMeasurement Fixture
Thermal Measurement Thermal Measurement
Measurement of RMeasurement of RJBJB
Slide 41
JT Therm al Characterization Param eter:Junction-to-Package Top
Definition
What it means?
- It provides correlation between die temperature and temperature of packageat top center.
- It is not true thermal resistance. Also, is not RJC. Variable with air flow.- It is about 5-10X smaller than RJC.
Application of Junction to Package top thermal characterizationparameter?
- Used to estimate the junction temperature from a measurement of top ofpackage in actual applications environment.
How to measure this value?
- Mount package on standard JEDEC thermal test board- Mount thermocouple on top center of the package- Put package in standard test environment Wind tunnel or JEDEC enclosure- Apply known amount of power- Measure temperature of die TJUNCTION and temperature at top center of
package TTOP
- Perform calculation using definition
POWER
TT TOPJUNTIONJT
Slide 42
Measurement of JT
P
TT TSSJJT JAJTJAR
Thermal MeasurementThermal Measurement
DefinitionDefinition
Thermocouple LocationThermocouple Location
Relationship with RjaRelationship with Rja
Slide 43
JB Therm al C haracteriza tion P aram eter:Junction -to -B oard
Definition
What it means?
- It provides correlation between die temperature and board temperature nearto the package.
- It is not true thermal resistance. Very close to RJB since 80-90% of an diepower flows into the PCB.
- New parameter does not have wide usage yet.- It is defined for both natural and forced air coditions.
Application of Junction to Board thermal characterization parameter?
- Used to estimate the die junction temperature from a measurement of boardin actual applications.
How to measure this value?
- Mount package on standard JEDEC thermal test board- Mount thermocouple on board at edge of the package- Put package in standard test environment Wind tunnel or JEDEC enclosure- Apply known amount of power- Measure temperature of die TJUNCTION and temperature of the board near to
the package.-
Perform calculation using definition.
POWER
TT BOARDJUNTIONJB
Slide 44
Measurement of JB
P
TT BJJB
Thermal MeasurementThermal Measurement
DefinitionDefinition
Thermocouple LocationThermocouple Location
TB
Slide 45
Other related equations
SACSJCJA
JAJTJA
Note: Package jc is very important for heat sink selection
Slide 46
Package with Heat Sink
Silicon DiePackage
Interface MaterialResistance(Assumed 0.2°C/W)
Rja = Rjc+Rcs+Rsa
Ta
Rsa - Heat sink
Rcs - Interface
Rjc - Package
Slide 47
How to select a Heat Sink How to select a Heat Sink
Simulated data of FC package shows case to junction thermal resistance as (Rjc) 0.2°C/W.
Assume the heat sink interface material thermal resistance to be (Rcs) 0.1°C/W
Case 1: Required Rja = 1.67°C/W (P=15 W, Ta = 85°C, Tj = 110°C)
Case 2: Estimated Rja=4.00°C/W (P=15 W, Ta = 50°C, Tj = 110°C)
Required heat sink thermal resistance is,Case 1: Rsa = 1.37°C/W Case 2: Rsa = 3.70°C/W
Slide 48
Heat Sink
Rsa=2.6°C/W at 200 LFM
Rsa= 1.37°C/WCase 1
Rsa= 3.7°C/WCase 2
#Case 1: Required minimum air flow of 100 LFM#Case 2: Required minimum air flow of 440 LFM
Ensure minimum air flow of # next to the package to maintain the temperature below Tj < 110°C
Slide 49
How to calculate die junction temperature How to calculate die junction temperature in an application environment? in an application environment?
Example 1:
Use of PSI-jt to estimate the junction temperature in an application environment,
Assume that the measured temperature at top center of the package is 95°C with customer application then,
Use the value of PSI-jt which measured based on JEDEC 4 layer board, at 400 lfpm forced convection cooling is PSI-jt =4.7 C/W,
then use equation: Tj = Pd x PSI-jt + Tt
At given power of 2.6 watts, Tj =2.6 W x 4.7 C/W + 95°C = 12.2°C + 95°C = 107.2°C
This is below the die maximum junction temperature specification requirement of 125°C.
Slide 50
How to calculate die junction temperature How to calculate die junction temperature in an application environment? in an application environment?
Example 2:
Use of PSI-jb to estimate the junction temperature in an application environment,
Assume that the board temperature measured near to the package is 60°C with customer application then,
Use the value of PSI-jb which measured based on JEDEC 4 layer board, at 400 lfpm forced convection cooling is PSI-jb = 11.0 C/W,
then use equation: Tj = Pd x PSI-jb + Tb
At given power of 2.6 watts, Tj =2.6 W x 11.0 C/W + 60°C = 28.6°C + 60°C = 88.6°C
This is below the die maximum junction temperature specification requirement of 125°C.
Slide 51
Package Thermal Simulation Package Thermal Simulation
Slide 52
Not drawn to scaleUnderfill + Bumps
Lid
Solder Balls
Lid attach epoxy
Ceramic Substrate
Die
FLIP CHIP Package FLIP CHIP Package Cross SectionCross Section
Slide 53
Thermal characterization of FCThermal characterization of FC--CBGA packageCBGA package
To study the effect of lid on package To study the effect of lid on package thermal performancethermal performance
To understand the package thermal To understand the package thermal performance using different heat sinks.performance using different heat sinks.
Thermal Simulation Thermal Simulation -- PackagePackage
Slide 54
Lid - Composite material with a high thermal conductivity value.
Thermal conductivity - >150 W/mK
The coefficient of thermal expansion (CTE) of the lid is matched - the die and the substrate.
Low Density Light weight
Benefits of LidBenefits of Lid
Slide 55
Input dataHeat flux : 5 to 10 W/cm2
Junction temperature : 110°C (max)Environment temperature : 70°C
Required Package Thermal Resistance : < 3.0Required Package Thermal Resistance : < 3.0°°C/WC/W
Simulation/Measurement ConditionsAmbient temperature : 25°C Test boards : High Conductivity as per JEDEC
Thermal PredictionsJunction Temperature (Tj) in °C Thermal Resistance in °C/WThermal Characterization parameter in °C/W
Package Thermal RequirementPackage Thermal Requirement
Slide 56
SgradVdivt
)()(
Transient + Convection Diffusion = Source V
Governing EquationGoverning Equation
- Commercial CFD Tool- Finite Volume Method- Grid Size: 135 x 125 x 85 (over 1.4 millions)- Radiation and Turbulence - Included
Slide 57
Environmental conditions- Natural convection
In still air- Forced Convection
Airflow Speed: 1.0 m/s & 2.5 m/s
Geometric variations- Lidded Vs Unlidded
- Heat Sinks: Passive & Active- Small & Large
Thermal Simulation/MeasurementThermal Simulation/Measurement
Slide 58
Thermal Model Thermal Model -- Flip Chip PackageFlip Chip Package
Lidded
Unlidded
Package with HS - 2D View
PCB, Package & HS
Slide 59
Thermal Model Thermal Model -- Different viewDifferent viewLidLid-die-attach
Die
SubstrateC4 & Under fill
Lid attachSolder balls
Slide 60
Natural ConvectionNatural ConvectionAirflow & Temperature patternAirflow & Temperature pattern
AirflowAirflow Temperature Temperature
Ta = 25°C2S2P PCB
Slide 61
LiddedLidless
Lidless with HS-L Lidded with HS-L
Tj=92.5°C
Tj=157.7°C Tj=132.8°C
Tj=89.4°C
Natural Convection Natural Convection Junction Temperature (Ta = 25Junction Temperature (Ta = 25°°C)C)
Slide 62
Results Results
Forced ConvectionForced Convection
Airflow Velocity: 2.5m/sAirflow Velocity: 2.5m/s
Slide 63
Airflow2.5 m/s
Without HS
With HSAirflow2.5 m/s
Forced Convection Forced Convection Typical Airflow Pattern Typical Airflow Pattern
Slide 64
Ta = 25°C2S2P PCB
Airflow 2.5m/s
Forced Convection Forced Convection Temperature DistributionTemperature Distribution
Slide 65
Tj=106.3°C Tj=85.1°C
Lidless Lidded
Lidless with HS-L
Tj=46.4°C
Lidded with HS-L
Tj=45.7°C
Forced Convection Forced Convection Junction Temperature (Ta = 25Junction Temperature (Ta = 25°°C) C)
Slide 66
Package Thermal Resistance Package Thermal Resistance Simulated Vs Measurement Simulated Vs Measurement
Thermal Resistance: FC-CBGA Package
0
2
4
6
8
10
0 200 400 600
Airflow in LFPM
Th
erm
al R
esis
tan
ce in
°C
/W
Measured
Simulated
Results shows good correlation between measured and simulated data
Slide 674.5 Infrared thermal analysis
FC_CBGA Lidded and Lidded and Unlidded andPackage HS-L HS-S HS-L
Top + Side 22% 57% 51% 62%Bottom 78% 43% 49% 38%
Top + Side 35% 79% 71% 81%Bottom 65% 21% 29% 19%
Package level Thermal Budget
Lidded
Natural Convection Still Air
Forced Convection V = 2.5 m/s
Package Thermal BudgetPackage Thermal Budget
Slide 68
How to calculate die junction temperature How to calculate die junction temperature in an application environment?in an application environment?
Example 1:
Use of jt to estimate the junction temperature in an application environment,
Assume that the measured temperature at top center of the package is 95°C with customer application then,
Use the value of jt which measured based on JEDEC 4 layer board, at 400 lfpm forced convection cooling is jt =4.7 C/W,
then use equation: Tj = Pd x jt + Tt
At given power of 2.6 watts, Tj =2.6 W x 4.7 C/W + 95°C = 12.2°C + 95°C = 107.2°C
This is below the die maximum junction temperature specification requirement of 125°C.
Slide 69
Thermal simulation estimate shows that FC package will meet the required junction to ambient thermal resistance of < 3.0°C/W.
Require external heat sink with forced air flow for heat flux > 4.0 W/cm2
Lidded Vs Lidless:
No heat sink attached: Improved thermal performance by ~23% with lid in still and forced air.
Heat sink 1 or 2 attached: Improved thermal performance by ~5% in still air with lid & no significant improvement in forced air.
Excellent correlations between numerical and measured data: < 12% error range
Simulation OutcomeSimulation Outcome
Slide 70
ReferencesReferences
www. electronics-cooling.comwww.coolingzone.comwww.jedec.orgwww.thermengr.com
HDI(Magazine High Density Interconnect)Advanced Packaging magazineASME, Int. Jl. of Electronic PackagingIEEE Trans. on Advanced PackagingIEEE Trans. on Components and Packaging TechnologiesIEEE Trans. on Electronics Packaging Manufacturing
Slide 71
THANK YOU