thermal management for electronic packaging

Thermal Management for Electronic Packaging

Guoping XuSun Microsystems

03/02/2006

CSE291: Interconnect and Packaging, UCSD, Winter 2006

OutlineIntroductionHeat transfer theoryThermal resistance in electronic packaging Thermal designThermal modelingThermal measurement


IntroductionFunctions of Electronic Packaging

Package protectionSignal distributionPower distributionHeat dissipation


IntroductionPackaging Hierarchy

ChipPackageBoardSystemRackRoom


IntroductionHigh end chip power trend

0

100

200

300

400

500

600

1990 1995 2000 2005 2010 2015 2020Year

CPU

Pow

er, (

W)

UltraSparc [1]Power 4 [2]Itanium 2 [3]ITRS 2002 [4]ITRS 2005


IntroductionCost performance chip power trend

0

20

40

60

80

100

120

140

160

2004 2006 2008 2010 2012 2014Year

CPU

Powe

r, (W

)

ITRS 2005


IntroductionPower density in datacom equipment


IntroductionPower density in datacom equipment Total power: 24KW Footprint: 15 sq. ft Power density: 1600W/sq. ft

Sun Fire E25K


IntroductionImpact of Device junction temperature

Computing performanceReliabilityFire hazard and/or Safety issues


Heat Transfer TheoryConduction

Definition: Conduction is a mode of heat transfer in which heat flows from a region of higher temperaure to one of lower temperature within a medium (solid, liquid, or gases) or media in direct physical contactFourier's law: Q = -KA(dT/dX)1-D conduction: Q = -KA (T1-T2)/LThermal resistance: R = (T1-T2)/Q = L/(KA)


Heat Transfer TheoryConduction

Contact thermal resistance


Heat Transfer TheoryThermal conductivity of various packaging materials

Material W/mKAluminum (pure) 216Aluminum Nitride 230

Alumina 25Copper 398

Diamond 2300Epoxy (No fill) 0.2

Epoxy (High fill) 2.1Epoxy glass 0.3

Gold 296Lead 32.5

Silicon 144Silicon Carbide 270Silicon Grease 0.2

Solder 49.3


Heat Transfer TheoryConvection

Convection: is a mode of heat transport from a solid surface to a fluid and occurs due to the bulk motion of the fluid.Newton's law: Q= hA (Tw- Tf)Convective thermal resistance: R= 1/(hA)Effects of heat transfer coefficient

Convetion mode: Natural convection, Foreced convection, phase changeFlow regime: Laminar, Turbulent flowFlow velocitySurface conditionFluid

Tf

Tw

Fluid

Velocity distribution

Temperature distribution

y y

Heated surface

u(y) T(y)


Heat Transfer TheoryTypical values of the heat transfer coefficient


Heat Transfer TheoryRadiation

Definition: Radiation heat transfer occurs as a result of radiant energy emitted from a body by virtue of its temperature.


Thermal Resistance-Package without heat sink

Rja: Junction to air thermal resistanceRja= (Tj-Ta)/PLow value is good thermal perfromance

Rjc: Junction to case thermal resistanceRjc = (Tj-Tc)/P

Ψjt: Thermal characterization parameter: Junction to package top, NOT thermal resistance.Ψjb: Thermal characterization parameter: Junction to board

TaTjTb

PCBPackage

Chip Tt


TjPackage

Heat sink

Die

Ts

Ta

Rja: Junction to air thermal resistanceRja= (Tj-Ta)/P=Rjc +Rcs+Rsa

Rjc: Junction to case thermal resistanceRjc = (Tj-Tc)/P

Rsa: External heat sink thermal resistanceRsa= (Ts-Ta)/P

Tc

Thermal Resistance-Package with heat sink


Thermal Resistance-PBGA package example

Tair


Thermal Resistance-Impact factors for package without heat sink

Die sizePackage size, lead countPackaging material thermal condunctivityMaterial thickness in major heat flow pathNumber of viasHeat spreader or heat slugAir velocity and temperaturePC Board sizeBoard configuration and material Board layout


Thermal DesignConduction application

Q

SubstrateTjTc

Tc = Tj - QL/(KA)

Uniform heating on the die

DieLayer 1Layer 2Layer iLayer N

ti

Kin-plane

KTthrough

Single material Composite material


Thermal DesignConduction application

SubstrateDie

bbabb

bbabb

sbb

sbsb HRAk

HRAkAAkAAR

tanh1tanh

sb AA132

Ab: Heat spreader base area

As: Heat source area

Hb: Heat spreader thickness

Kb: Heat spreader thermal conductivity

Heat spreader


Thermal DesignConvection application-Heat sink design

W

L

H

Hf

Hb b tf

Heat sink base

Fins



Thermal resistance:

Heat transfer:

Fin efficiency: f

ff mH

mH )tanh( f

t

fo A

A 11

)1(

1..

pot cmhAp

inletbba

ecmQTTR

54.7air

hkhDNu

45.0786.0 PrRe024.0air

hkhDNu

Laminar flow

Turbulent flow



Total static pressure loss:

24

2ch

eh

appcUK

DLfKP

Culham and Muzychka (2001) David Copeland (2000) Apparent friction factor fapp calculation

21

225.0* Re44.3Re

fLfapp

212

257.0* Re2.3Re

fLf app

Fully developed flow friction factor f

5

43

2

089.6

954.22829.40

721.46527.3224Re

f

ff

ff

Hb

HbHb

HbHbf

2

2

1

164.197.4Re

f

f

Hb

Hbf

Contraction loss coefficient Kc

142.0cK

24.08.0 cK

Expansion loss coefficient Ke

21 eK

4.01 2 eK

Re*

hDLL

btb

WNt

f

f

1


Thermal DesignConvection application- Heat sink design Impact factors

Air flow rateAvailable spaceHeat sink base and fin materialFin pitch and fin thicknessHeat fluxHeat sink technologies


Thermal DesignDesign methodology

Define requirementsAnalyze given package designIdentify major heat paths and paths for improvementsConsider and assess potential improvementsDetail analysis/modeling Build prototypesThermal testing


ModelingFinite Element Method (FEM)

Software: ANSYSSolve conduction problem within package or boardRequire input data: material propoerties, package/board construction/geometryBoundary conditions:

Heat source distribution on the die or boardEffective convective heat transfer coefficient on the surface of the package or board


ModelingFinite Element Method

Procedure:Create package/board geometry or import from CAD fileMeshInput material properties and assign boundary conditionsSolvePost-process


ModelingFinite Difference Method (FDM )

Computational Fluid Dynamics (CFD)Commercial software: Flotherm, FluentSolve the temperature field and flow fieldNot only solve the conduction, also on convection, radiation and phase changeRequired input: Geometry, flow conditions, material properties including fluidMesh dependent on the chosed model


ModelingFinite Difference Method (FDM ) Example


MeasurementPackaging thermal parameters

Mount package on a standard test boardMount thermocouple on top of the package center Mount thermacouple on board at the edge of packagePut package in a standard test environment

Wind tunnel to vary the air speedApply known amount of powerMeasure temperature of Tj, Ta, Tb, Tt Calculate Rja, Ψjt, Ψjb

TaTjTb

PCB test boardPackage

Chip Tt


MeasurementPackaging thermal parameters


MeasurementPackaging thermal resistance Rjc

All heat is removed from top of the package


MeasurementThermal interface material resistance Rcs


MeasurementHeat sink thermal resistance Rsa

T 4

A ir flow

T in l e t T o u t l e t

T s T 2 T 3

H e a t e r s C o ppe r b loc k

I n sula t ion

T he r m a l int e r f ac e m a te ri a l

No z z le A ir f low te s t c ha m b e r

p p 2

B lo wer

D i m e ns i on s a r e n o t s c a l e d

Heat sink

QTTR inlets

sa

LTTAkQ ss

23

Heat source size: 25 mm x 25 mm


MeasurementHeat sink thermal resistance Rsa

0.000

0.100

0.200

0.300

0.400

0.500

0.600

0 0.01 0.02 0.03 0.04 0.05Flow rate (m3/s )

Ther

mal

Res

ista

nce,

( o C

/ W )

Test dataPresent method (Eqs. 6-8)Teertstra [1]Copeland [2]


Q & A

Guoping [email protected]

thermal management for electronic packaging

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