Thermal Management for Electronic Packaging

Thermal Management for Electronic Packaging 03/02/2006 Guoping Xu Sun Microsystems CSE291: Interconnect and Packaging, UCSD, Winter 2006 Outline I...
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Thermal Management for Electronic Packaging 03/02/2006

Guoping Xu Sun Microsystems

CSE291: Interconnect and Packaging, UCSD, Winter 2006

Outline Introduction Heat transfer theory Thermal resistance in electronic packaging Thermal design Thermal modeling Thermal measurement

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CSE291: Interconnect and Packaging, UCSD, Winter 2006

Introduction Functions of Electronic Packaging Package protection Signal distribution Power distribution Heat dissipation

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CSE291: Interconnect and Packaging, UCSD, Winter 2006

Introduction Packaging Hierarchy Chip Package Board System Rack Room

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CSE291: Interconnect and Packaging, UCSD, Winter 2006

Introduction High end chip power trend 600

CPU Power, (W)

500 400

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

300 200 100 0 1990

1995

2000

2005

2010

2015

2020

Year

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CSE291: Interconnect and Packaging, UCSD, Winter 2006

Introduction Cost performance chip power trend 160 140

ITRS 2005

CPU Power, (W)

120 100 80 60 40 20 0 2004

2006

2008

2010

2012

Year

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2014

CSE291: Interconnect and Packaging, UCSD, Winter 2006

Introduction Power density in datacom equipment

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CSE291: Interconnect and Packaging, UCSD, Winter 2006

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

Sun Fire E25K

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CSE291: Interconnect and Packaging, UCSD, Winter 2006

Introduction Impact of Device junction temperature Computing performance Reliability Fire hazard and/or Safety issues

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CSE291: Interconnect and Packaging, UCSD, Winter 2006

Heat Transfer Theory Conduction 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 contact

Fourier's law: Q = -KA(dT/dX) 1-D conduction: Q = -KA (T1-T2)/L Thermal resistance: R = (T1-T2)/Q = L/(KA)

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CSE291: Interconnect and Packaging, UCSD, Winter 2006

Heat Transfer Theory Conduction Contact thermal resistance

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CSE291: Interconnect and Packaging, UCSD, Winter 2006

Heat Transfer Theory Thermal conductivity of various packaging materials Material Aluminum (pure) Aluminum Nitride Alumina Copper Diamond Epoxy (No fill) Epoxy (High fill) Epoxy glass Gold Lead Silicon Silicon Carbide Silicon Grease Solder

W/mK 216 230 25 398 2300 0.2 2.1 0.3 296 32.5 144 270 0.2 49.3

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CSE291: Interconnect and Packaging, UCSD, Winter 2006

Heat Transfer Theory Convection 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 change Flow regime: Laminar, Turbulent flow Flow velocity y Tf Fluid y Surface condition Fluid Velocity distribution

u(y)

Heated surface

Temperature distribution

Tw T(y)

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CSE291: Interconnect and Packaging, UCSD, Winter 2006

Heat Transfer Theory Typical values of the heat transfer coefficient

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CSE291: Interconnect and Packaging, UCSD, Winter 2006

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

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CSE291: Interconnect and Packaging, UCSD, Winter 2006

Thermal Resistance -Package without heat sink Ta

Tb

Chip

Tt Tj Package PCB

Rja: Junction to air thermal resistance Rja= (Tj-Ta)/P Low value is good thermal perfromance

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

Ψjt: Thermal characterization parameter: Junction to package top, NOT thermal resistance. Ψjb: Thermal characterization parameter: Junction to board Page 16

CSE291: Interconnect and Packaging, UCSD, Winter 2006

Thermal Resistance -Package with heat sink Ta Heat sink Package Die

Ts Tc Tj

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

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

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

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CSE291: Interconnect and Packaging, UCSD, Winter 2006

Thermal Resistance -PBGA package example

Tair Page 18

CSE291: Interconnect and Packaging, UCSD, Winter 2006

Thermal Resistance -Impact factors for package without heat sink Die size Package size, lead count Packaging material thermal condunctivity Material thickness in major heat flow path Number of vias Heat spreader or heat slug Air velocity and temperature PC Board size Board configuration and material Board layout

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CSE291: Interconnect and Packaging, UCSD, Winter 2006

Thermal Design Conduction application Single material Q Die Substrate

Tc Tj

Tc = Tj - QL/(KA)

ti

Composite material Kin-plane Layer 1 Layer 2 Layer i Layer N KTthrough

Uniform heating on the die

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CSE291: Interconnect and Packaging, UCSD, Winter 2006

Thermal Design Conduction application Heat spreader Die Substrate

Ab  As kb Ab R ba  tanh H b  Rsb  kb Ab As 1  kb Ab R ba tanh H b 

23 1   Ab As Ab: Heat spreader base area As: Heat source area Hb: Heat spreader thickness Kb: Heat spreader thermal conductivity Page 21

CSE291: Interconnect and Packaging, UCSD, Winter 2006

Thermal Design Convection application-Heat sink design

Hf

b H

tf

Fins Hb L

Heat sink base W

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CSE291: Interconnect and Packaging, UCSD, Winter 2006

Thermal Design Convection application-Heat sink design Thermal resistance:

Heat transfer:

Rba

Tb  Tinlet   Q

hDh Nu   7.54 k air

Fin efficiency:

o  1 

At

1   f 

.

.

m c p (1  e

 hAto m c p

Laminar flow

hDh Nu   0.024 Re 0.786 Pr 0.45 k air

Af

1

Turbulent flow

f 

tanh( mH f ) mH f Page 23

)

CSE291: Interconnect and Packaging, UCSD, Winter 2006

Thermal Design Convection application-Heat sink design Total static pressure loss:   U ch 2 L P   K c  4 f app  K e   Dh 2   Culham and Muzychka (2001) Apparent friction factor fapp calculation

Fully developed flow friction factor f

 

 f app Re  3.44 L* 



L Dh Re





2

  f Re   

 2  40.829b H f 3  22.954b H f 4 5  6.089b H f 

f Re  24  32.527 b H f  46.721 b H f

Contraction loss coefficient Kc Expansion loss coefficient Ke L* 

0.5  2

David Copeland (2000) 12

  1

f app

 

 Re  3.2 L* 

 0.57  2



2

  f Re   

b H f 2  1 f Re  4.7  19.64 b H f  12

K c  0.421   

K c  0.8  0.4 2

K e  1   2

K e  1   2  0.4

Nt f W



b tf b

12

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CSE291: Interconnect and Packaging, UCSD, Winter 2006

Thermal Design Convection application- Heat sink design Impact factors Air flow rate Available space Heat sink base and fin material Fin pitch and fin thickness Heat flux Heat sink technologies

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CSE291: Interconnect and Packaging, UCSD, Winter 2006

Thermal Design Design methodology Define requirements Analyze given package design Identify major heat paths and paths for improvements Consider and assess potential improvements Detail analysis/modeling Build prototypes Thermal testing

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CSE291: Interconnect and Packaging, UCSD, Winter 2006

Modeling Finite Element Method (FEM) Software: ANSYS Solve conduction problem within package or board Require input data: material propoerties, package/board construction/geometry Boundary conditions: Heat source distribution on the die or board Effective convective heat transfer coefficient on the surface of the package or board

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CSE291: Interconnect and Packaging, UCSD, Winter 2006

Modeling Finite Element Method Procedure: Create package/board geometry or import from CAD file Mesh Input material properties and assign boundary conditions Solve Post-process

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CSE291: Interconnect and Packaging, UCSD, Winter 2006

Modeling Finite Difference Method (FDM ) Computational Fluid Dynamics (CFD) Commercial software: Flotherm, Fluent Solve the temperature field and flow field Not only solve the conduction, also on convection, radiation and phase change Required input: Geometry, flow conditions, material properties including fluid Mesh dependent on the chosed model

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CSE291: Interconnect and Packaging, UCSD, Winter 2006

Modeling Finite Difference Method (FDM ) Example

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CSE291: Interconnect and Packaging, UCSD, Winter 2006

Measurement Packaging thermal parameters Mount package on a standard test board Mount thermocouple on top of the package center Mount thermacouple on board at the edge of package Put package in a standard test environment Wind tunnel to vary the air speed

Apply known amount of power Measure temperature of Tj, Ta, Tb, Tt Calculate Rja, Ψjt, Ψjb Ta Tt Chip Tj Tb Package PCB test board Page 31

CSE291: Interconnect and Packaging, UCSD, Winter 2006

Measurement Packaging thermal parameters

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CSE291: Interconnect and Packaging, UCSD, Winter 2006

Measurement Packaging thermal resistance Rjc All heat is removed from top of the package

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CSE291: Interconnect and Packaging, UCSD, Winter 2006

Measurement Thermal interface material resistance Rcs

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CSE291: Interconnect and Packaging, UCSD, Winter 2006

Measurement Thermal interface material resistance Rcs

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CSE291: Interconnect and Packaging, UCSD, Winter 2006

Measurement p et

tl

T ou

p ir flow

A



t

le

in

T

2



4

T

Heat sink thermal resistance Rsa

wer

lo

B

le

zz

No

er

b

m

ha

stc

te

low

irf

A rs

te

ea

Rsa 

Ts  Tinlet Q

Q  k s As

d

le

a

c

ts

o

n

re

a

s

ion

ns

e

im

D

tion

sula

In

H

k

loc

b

r

pe

o

C

3

T

al

ri

ate

em

fac

2

T

al

rm er

he

T int

s

T

Heat sink

T3  T2 L

Heat source size: 25 mm x 25 mm

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CSE291: Interconnect and Packaging, UCSD, Winter 2006

Measurement Heat sink thermal resistance Rsa The rmal Re s is tanc e , ( o C/ W )

0.600 Test data Present method (Eqs. 6-8) Teertstra [1] Copeland [2]

0.500 0.400 0.300 0.200 0.100 0.000 0

0.01

0.02 0.03 3 Flow rate (m /s )

0.04

0.05

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CSE291: Interconnect and Packaging, UCSD, Winter 2006

Q&A

Page 38

Guoping Xu [email protected]