Post on 16-Feb-2018
Thermal Management for Electronic Packaging
Guoping XuSun Microsystems
03/02/2006
CSE291: Interconnect and Packaging, UCSD, Winter 2006
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OutlineIntroductionHeat transfer theoryThermal resistance in electronic packaging Thermal designThermal modelingThermal measurement
CSE291: Interconnect and Packaging, UCSD, Winter 2006
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IntroductionFunctions of Electronic Packaging
Package protectionSignal distributionPower distributionHeat dissipation
CSE291: Interconnect and Packaging, UCSD, Winter 2006
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IntroductionPackaging Hierarchy
ChipPackageBoardSystemRackRoom
CSE291: Interconnect and Packaging, UCSD, Winter 2006
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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
CSE291: Interconnect and Packaging, UCSD, Winter 2006
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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
CSE291: Interconnect and Packaging, UCSD, Winter 2006
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IntroductionPower density in datacom equipment
CSE291: Interconnect and Packaging, UCSD, Winter 2006
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IntroductionPower density in datacom equipment Total power: 24KW Footprint: 15 sq. ft Power density: 1600W/sq. ft
Sun Fire E25K
CSE291: Interconnect and Packaging, UCSD, Winter 2006
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IntroductionImpact of Device junction temperature
Computing performanceReliabilityFire hazard and/or Safety issues
CSE291: Interconnect and Packaging, UCSD, Winter 2006
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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)
CSE291: Interconnect and Packaging, UCSD, Winter 2006
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Heat Transfer TheoryConduction
Contact thermal resistance
CSE291: Interconnect and Packaging, UCSD, Winter 2006
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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
CSE291: Interconnect and Packaging, UCSD, Winter 2006
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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)
CSE291: Interconnect and Packaging, UCSD, Winter 2006
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Heat Transfer TheoryTypical values of the heat transfer coefficient
CSE291: Interconnect and Packaging, UCSD, Winter 2006
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Heat Transfer TheoryRadiation
Definition: Radiation heat transfer occurs as a result of radiant energy emitted from a body by virtue of its temperature.
CSE291: Interconnect and Packaging, UCSD, Winter 2006
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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
CSE291: Interconnect and Packaging, UCSD, Winter 2006
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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
CSE291: Interconnect and Packaging, UCSD, Winter 2006
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Thermal Resistance-PBGA package example
Tair
CSE291: Interconnect and Packaging, UCSD, Winter 2006
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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
CSE291: Interconnect and Packaging, UCSD, Winter 2006
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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
CSE291: Interconnect and Packaging, UCSD, Winter 2006
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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
CSE291: Interconnect and Packaging, UCSD, Winter 2006
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Thermal DesignConvection application-Heat sink design
W
L
H
Hf
Hb b tf
Heat sink base
Fins
CSE291: Interconnect and Packaging, UCSD, Winter 2006
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Thermal DesignConvection application-Heat sink design
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
CSE291: Interconnect and Packaging, UCSD, Winter 2006
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Thermal DesignConvection application-Heat sink design
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
CSE291: Interconnect and Packaging, UCSD, Winter 2006
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Thermal DesignConvection application- Heat sink design Impact factors
Air flow rateAvailable spaceHeat sink base and fin materialFin pitch and fin thicknessHeat fluxHeat sink technologies
CSE291: Interconnect and Packaging, UCSD, Winter 2006
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Thermal DesignDesign methodology
Define requirementsAnalyze given package designIdentify major heat paths and paths for improvementsConsider and assess potential improvementsDetail analysis/modeling Build prototypesThermal testing
CSE291: Interconnect and Packaging, UCSD, Winter 2006
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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
CSE291: Interconnect and Packaging, UCSD, Winter 2006
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ModelingFinite Element Method
Procedure:Create package/board geometry or import from CAD fileMeshInput material properties and assign boundary conditionsSolvePost-process
CSE291: Interconnect and Packaging, UCSD, Winter 2006
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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
CSE291: Interconnect and Packaging, UCSD, Winter 2006
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ModelingFinite Difference Method (FDM ) Example
CSE291: Interconnect and Packaging, UCSD, Winter 2006
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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
CSE291: Interconnect and Packaging, UCSD, Winter 2006
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MeasurementPackaging thermal parameters
CSE291: Interconnect and Packaging, UCSD, Winter 2006
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MeasurementPackaging thermal resistance Rjc
All heat is removed from top of the package
CSE291: Interconnect and Packaging, UCSD, Winter 2006
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MeasurementThermal interface material resistance Rcs
CSE291: Interconnect and Packaging, UCSD, Winter 2006
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MeasurementThermal interface material resistance Rcs
CSE291: Interconnect and Packaging, UCSD, Winter 2006
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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
CSE291: Interconnect and Packaging, UCSD, Winter 2006
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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]
CSE291: Interconnect and Packaging, UCSD, Winter 2006
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Q & A
Guoping XuGuoping.xu@sun.com