Electronic Packaging and Manufacturing...
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Electronic Packaging Electronic Packaging and Manufacturing Thermal Management mech14.weebly.com
Transcript of Electronic Packaging and Manufacturing...
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Electronic Packaging and
Manufacturing
Thermal Management
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What is Heat Transfer?
Heat transfer is energy in transit due to a temperature difference
Temperature gradient has to exist - heat flow will be in a direction so as to equalize the temperature
at various points.
3 Modes: Conduction, Convection, & Radiation
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Another important quantity is the HEAT FLUX, which is the rate of heat transfer per unit area.
Consider the silicon die in a IC Package below:
Power dissipated by the die = q [Watts]
Area of the die = A [cm2]
Heat Flux:
Consider a CPU die :
Power: q = 25 W
Area: A = 0.8 cm2
Therefore, the heat flux through the die is:
q” = 31.25 W/cm2
][" 2cmW
A
Concept of Heat Flux (q”)
dieheat sink
Package substrate
T1
T2
q”T1 > T2
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Thermal Resistance - Conduction
Thermal resistance is a method used to represent thermal systems
Thermal resistance is analogous to electrical resistance
• Electrical resistance associated with transport of electricity
• Thermal resistance associated with transport of heat
L
TkA
L
TTkAq
12
)Resistance Thermal(
TT
L
kAq
kA
LResistance Thermal
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Thermal Resistance and Ohm’s Law
Electrical Resistance
Voltage A
Voltage B
Current
R =Voltage A - Voltage B
Current
Units: Ohm
LsA
Electrical
Resistance=
Thermal Resistance
Temperature A
Temperature B
Power
Dissipation
qAB
=
Temp A - Temp B
Power Dissipation
Units: °C/Watt
LkA
Conduction
Thermal
Resistance
=
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Energy transfer between a surface and a fluid moving over the surface.
As, Ts
Convection – Newton’s Law of Cooling
q”
TThq s• The heat flux is defined as
• The total heat flow is defined as TTAhq ss
• Convective heat transfer coefficient h
– Boundary conditions
– Surface geometry
– Fluid and fluid motion
Challenge lies in determination of h
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Commonly Used Nomenclature
X and Y could be
A: ambient
B: PCB board
C: case
J: junction
L: lead
P: thermal plate
S: heat sink
qXY
= X to Y thermal resistance
qJC
qJA
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Understanding Heat Transfer Paths
Consider the PGA package
Substrate
Cu Heat Spreader
Kovar Pins
Acknowledgments: Intel Corporation
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Heat Transfer Paths: PGA Example
Conduction Convection Radiation
Heat Sink
Socket PCB
PPGA
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gThermal Resistance Network: PGA
Example
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Thermal Architectures
ARCHITECTURE I – Bare Die
attach
• Heat sink interfaces with CPU
• Useful for mobile applications
ARCHITECTURE II – Integrated
Heat Spreader
• Heat sink interfaces with IHS
• Two interfaces
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Thermal Resistance: Bare Die attach
qJA
= qJS
+ qSA
Ta
Ts
Tj
qJS
qSA
qJA
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Thermal Resistance: Package with IHS
example
qJS
= qJC
+ qCS
qJA
= qJC
+ qCS
+ qSA
Ta
Tc
Tj
Ts
qJC
qSA
qJA
qCS
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3
Thermal Management Solutions
Desktop Systems Notebook Systems
Acknowledgments: Intel Corporationhttps://www.boydcorp.com
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q hA T Tb ( )
h T, h T,
A,Tb
Fin Heat Transfer
Atot = Ab + NfAfin
Fins increase surface area thus reducing 1/hA
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Heat Sink Characterization
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Heat Sink Characterization (cont.)
Heat sink thermal resistance corresponds to the operating point flow rate
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Heat Transfer calculations -
correlations
0
1/ 3
0
1 /
Re Pr
x
x ba
m
x x
NuNu
x
Nu C
Laminar Turbulent
Isothermal Isoflux Isothermal Isoflux
a 3/4 3/4 9/10 9/10
b 1/3 1/3 1/9 1/9
C 0.332 0.453 0.0296 0.0308
m 1/2 1/2 4/5 4/5
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Heat Transfer calculations - correlations
Flow over Cylinder: Churchill and Bernstein Correlation
4 / 55 / 81/ 2 1/ 3
1/ 42 / 3
0.62Re Pr Re0.3 1
282,0001 0.4 / Pr
D DDNu
Sphere
Isothermal Array of Cylinders
C, m and C2 can be found in look-up tables
1/ 41/ 2 2 / 3 0.42 0.4Re 0.06Re Pr / D D D sNu
1/ 40.36
2 ,maxRe Pr Pr/ Pr m
D D sNu C C
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Forced Convection – Internal Flow
Incropera and Dewitt, 6th Edition
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Vertical Flat Plate
Natural Convection
• Empirical Heat Transfer Correlations
Laminar Flow 910 :LRa
1/ 4
4 / 99 /16
0.6700.68
1 0.492 / Pr
LL
RaNu
2
1/ 6
4 / 99 /16
0.3870.825
1 0.492 / Pr
LL
RaNu
Turbulent Flow
Incropera and Dewitt, 6th Edition
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Horizontal flat plate
Facing up Facing down
Natural Convection
1/ 4 4 70.54 10 10L L LNu Ra Ra
1/ 3 7 110.15 10 10L L LNu Ra Ra
1/ 4 5 100.27 10 10L L LNu Ra Ra
sT TsT T
Incropera and Dewitt, 6th Edition
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Isothermal
plates:
Isoflux
plates:
Natural Convection through vertical channels
• Correlations of Bar Cohen and Rohsenow for
different boundary conditions
S S
Incropera and Dewitt, 6th Edition
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Pressure drop calculations
Fully Developed flow through a channel – pressure gradient along
the flow direction (x)
f is the friction factor
f = 64/ReD for laminar flow (ReD < 2000)
f -> read from Moody chart for turbulent flow (ReD > 2000)
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Moody Chart for friction factor (f)
Incropera and Dewitt, 6th Edition
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Problem -1
An electronic circuit board dissipating 50 W
is sandwiched between two ducted forced air
cooled heat sinks. The sinks are 150-mm in
length have 20 air passages of 6-mm x 25-
mm. Atmospheric air at a volumetric flow
rate of 0.06 m3/s and 300-K is drawn through
the sinks by a blower. Estimate the operating
temperature of the board and pressure drop
across the heat sinks.
Assuming air properties to be ν = 2 x 10-5
m2/s, Pr = 0.7, k = 0.03 W/m-K; Cp = 1.78
kJ/kg-K,
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Problem -2
A vertical array of printed circuit boards is immersed in quiescent ambient air at
17⁰C. Although the components on the board protrude from their substrates on the circuit boards, it is reasonable, as a first approximation, to assume them as flat
plates with uniform surface heat flux. Consider boards of length and width L = W
= 0.4m and spacing S = 25mm. If the maximum allowable temperature of the
board is 77⁰C, what is the maximum allowable power dissipation per board?
SL g
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Cold plate
Liquid Cooled Cold Plates
Source: https://www.lytron.com/Cold-Plates Acknowledgment: Intel
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Pumped Liquid Cooling solution
Finally, EVERY thermal solution is AIR COOLED
Prasher et al, 2006
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Heat pipe
Extraction
Rejection
TransportHeat pipe
• Very high thermal
conductivity
• Effective axial k ~10,000
W/m-K
• Means of transporting heat
from an “inconvenient” location to a “convenient” location
Mongia et al. 2007
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Refrigeration Cooling Techniques
COND
Compressor
Expansion
valve
Qin
Qout
• Heat Flow across adverse temperature gradient
• Needs external energy to drive compressor
Evap
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Thermoelectric Refrigeration
www.santarosa.edu/~yataiiya/E45/PROJECTS/peltier.ppt
http://cleantechnica.com/2014/06/13/
https://www.youtube.com/watch?v=2b2wAB1uTLI
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References:
“Packaging of Electronic Systems”, James W. Dally, McGraw-Hill
Education, 1990
“Fundamentals of Microsystems Packaging”, R. R. Tummala, McGraw Hill,
2001
“Fundamentals of Heat and Mass Transfer”, 6th Edition, Incropera and
Dewitt, Wiley 1998
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