nus cht course

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

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

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

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

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

???

Various Electronic PackagesVarious Electronic Packages

Source: www.electronics-cooling.com

Slide 12

Package Thermal PerformancePackage Thermal Performance


http://www.electronics-cooling.com


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

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


Major heat pathsPackage top to AirPackage Bottom to boardPackage leads to board

Heat Transfer in Electronic packagesHeat Transfer in Electronic packages

Slide 18


Heat Transfer in Electronic packagesHeat Transfer in Electronic packages




- 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



- Need for liquid cooling in the future of thermal management

Various Cooling in ElectronicsVarious Cooling in Electronics

Slide 22


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




- 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


- 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




Synthetic Jet ImpingementSynthetic Jet Impingement

Slide 26

NanolightningNanolightning


- 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).



Liquid coolingLiquid cooling


- 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


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



Different Advanced coolingDifferent Advanced cooling


Spray Cooling

Immersion Cooling

Mutiple Jet impingement Cooling

Slide 30

Thermal ConsiderationsThermal Considerations


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

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

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


Wind TunnelWind Tunnel

Thermal MeasurementThermal Measurement

TA

TJ

Die

Package

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


- 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



Heat flow with heat sinkHeat flow with heat sink

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.


- 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


Measurement FixtureMeasurement Fixture

Thermal Measurement Thermal Measurement

Measurement of RMeasurement of RJBJB

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.


- 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



Thermocouple LocationThermocouple Location

Relationship with RjaRelationship with Rja

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.


- 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



Thermocouple LocationThermocouple Location

TB

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

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

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



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

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

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

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

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

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

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

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

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



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

http://www.coolingzone.com

http://www.jedec.org

http://www.thermengr.com

THANK YOU

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