Investigation of Thermal Characterization of a Thermally Enhanced FC-PBGA Assembly

doi:10.4236/jectc.2013.33010

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Journal of Electronics Cooling and Thermal Control, 2013, 3, 85-93

http://dx.doi.org/10.4236/jectc.2013.33010 Published Online September 2013 (http://www.scirp.org/journal/jectc)

Investigation of Thermal Characterization of a Thermally

Enhanced FC-PBGA Assembly

C. F. Lin1, G. H. Wu1*, S. H. Ju2

1Department of Mechanical Engineering, National Cheng-Kung University, Tainan, Taiwan

2Department of Civil Engineering, National Cheng-Kung University, Tainan, Taiwan

Email: *[email protected], [email protected]

Received January 1, 2013; revised February 1, 2013; accepted February 10, 2013

permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

ABSTRACT

In this paper, three-dimensional finite element analysis using the commercial ANSYS software is performed to study

the thermal performance of a thermally enhanced FC-PBGA (flip-chip plastic ball grid array) assembly in both natural

and forced convection environments. The thermally enhanced FC-PBGA assembly is a basic FC-PBGA assembly with

a lid attached on top, after which an ex truded-fin heatsink is attached on the top of the lid. The finite element model is

complete enough to include key elements such as bumps, solder balls, substrate, printed circuit board, extruded-fin

heatsink, lid, vias, TIM1 (thermal interface material 1), TIM2 (thermal interface material 2), lid-substrate adhesive and

ground planes for both signal an d pow er. Temperature fields are simulated and presented for several package configura-

tions. Thermal resistance is calculated to characterize and compare the thermal performance by considering alternative

design parameters of the polymer-based materials and the thermal enhancement components. The polymer-based mate-

rials include underfill, TIM1, TIM2, lid-substrate adhesive and substrate core material. The specific thermal enhance-

ment components are the extruded-fin heatsink and the lid.

Keywords: Polymer-Based Materials; Flip-Chip Packaging; Finite Element Methods

1. Introduction

Due to increasing demand for high density, high I/O,

high performance electrical application and flip-chip pla-

stic ball grid array (FC-PBGA) packaging are rapidly be-

coming the package of choice. FC-PBGA technology

offers many advantages over the popular PBGA. Com-

monly stated advantages of FC-PBGA are higher pack-

aging density, shorter leads, lower inductance, better

noise control, smaller device footprint and lower package

profile [1]. A typical basic FC-PBGA assembly (i.e.

without thermal enhancement) is shown schematically in

Figure 1. Heat dissipated from the chip follows two ma-

jor paths. One path goes from the top of the chip to the

ambient environment. The other path goes from the chip

to the substrate to the solder balls to the PCB and finally

to the ambient.

Due to the rapid increase of power and packaging den-

sities, thermal issues have become critical factors for

reliability. Various thermal enhancements have been de-

veloped for the basic FC-PBGA package to improve

thermal performance. Gugliermermetti and Grignaffini [2]

analyzed theoretically the thermal performance of paral-

lel stacks of in-line plate fin heat sinks. They reported

that a fin efficiency parameter, like that used for constant

cross-section fin in an isothermal fluid flow, can be in-

troduced to express both the local and overall heat trans-

fer balances. Many numerical and experimental studies

in recent years have focused on thermal enhancement

techniques for FC-PBGA packages. Joiner [3] numeri-

cally and experimentally compared the thermal perform-

ance between a FC-CBGA with a heatsink and a FC-

PBGA with a heatsink. He reported that both FC-PBGA

and FC-CBGA packages can be used for relatively high

power applications. If a heatsink is implemented, then

both package types yield comparable thermal perform-

ance. Chen el al. [4] proposed a finite element method-

ology to predict the th ermal resistance of both FC-PBGA

with a bare die and FC-PBGA with a metal cap. They

reported that the material of the metal cap slightly influ-

enced the thermal resistance when the heat dissipation

was saturated through the metal cap. Luo el al. [5] ana-

lyzed by finite element methodology, a whole mobile

phone system, by observing the system response to one

*Corresponding a uthor.

C. F. LIN ET AL.

source. They reported that material with thermal conduc-

tivity can be added between the chip and the bottom case

to enhance the thermal management under natural con-

vection. Menon el al. [6] studied the thermal perform-

ance of the package on package structure in natural en-

vironments using finite element modeling methodology

and analyzing the effect of die power on the logic and

memory dies.

This present paper considers three-dimensional finite

element simulation of a thermally enhanced FC-PBGA

assembly in both natural and forced air convection envi-

ronments, using the commercial software ANSYS [7].

The thermally enhanced FC-PBGA assembly is a basic

FC-PBGA assembly with a lid attached on top, after

which an extruded-fin heatsink is attached on the top of

the lid, as seen in Figure 2 and denoted in the following

as an FC-PBGA/lid/heatsink assembly. The finite ele-

ment model is complete enough to include key elements

such as bumps, solder balls, substrate, printed circuit

board, extruded-fin heatsink, lid, vias, TIM1, TIM2, lid-

substrate adhesive and ground planes for both signal and

power. Temperature fields are simulated and presented

for several package configurations. Thermal resistance is

calculated to characterize and compare the thermal per-

formance by considering alternative design parameters of

the polymer-based materials and the thermal enhance-

ment components. The polymer-based materials include

underfill, TIM1, TIM2, lid-substrate adhesive and sub-

strate core material. The specific thermal enhancement

components are the extruded-fin heatsink and the lid.

2. Finite Element Modeling

2.1. Description of FC-PBGA/Lid/Heatsink

Assembly

In the following we consider an FC-PBGA/lid/heatsink

assembly, as seen in Figure 2. This assembly has a sili-

con chip size of 7.4 × 5.4 × 0.74 mm, with 256 solder

bumps distributed over the base. The chip is first bonded

to an organic substrate with solder bump interconnects.

The space between chip and substrate is then filled with

epoxy-based underfill material. The purpose of the un-

derfill is to release the thermo-mechanical stress of the

solder bumps due to coefficient of thermal expansion

mismatch between the silicon chip and the organic sub-

strate. The 25 × 25 × 1.0 mm substrate contains six bur-

ied metal layers and also a 0.05 mm solder mask layer o n

both the upper and lower surfaces. This FC-PBGA

package is mounted on a four-layer (2s2p) PCB with

solder balls 0.77 mm in diameter and 0.45mm in height.

The solder balls are patterned as a depopulated array in

which a 9 × 9 array of central balls is removed from a

full array of 19 × 19 solder balls. The 100 × 100 × 1.52

mm PCB also contains a 0.05 mm solder mask layer on

both top and botto m surfaces and is exposed to the air in

a horizontal package-up position, as seen in Figure 2.

The core material of the substrate is FR-5 laminate, while

the core material of the PCB is FR-4 laminate. Vias con-

nect various layers within the substrate and the PCB for

reasons of electrical and/or thermal conduction and have

a much higher thermal conductivity value (300 - 400

W/m K



) than the organic core material (0.2 - 0.4

W/m K



). Heat is conducted by the vias from the chip

through the solder balls and into the PCB in the out of

plane (Z) direction. The present finite element model

assumes that each solder ball or solder bump is associ-

ated with a through-via in the substate and in the PCB.

Vias in the substrate are solid copper with a diameter of

0.05 mm. Vias in the PCB are hollow copper with outer

and inner diameters of 0.25 and 0.20 mm, respectively.

An aluminum lid is attached on top of the substrate,

covering the chip. The contact b etween any two surfaces

Figure 1. A typical basic FC-PBGA assembly.

Figure 2. Cross section of the FC-PBGA/lid/heatsink assembly.

C. F. LIN ET AL. 87

creates a resistance that may greatly reduce heat conduc-

tion efficiency across the contact surface unless a thermal

interface material (TIM) is used. A soft pad is applied

between the chip and the lid. The soft pad is silicone

elastomers filled with high conductivity particles such as

boron nitride and has a thermal conductivity of 3.7

and denoted in the following as TIM1. The lid

has a typical thickness of 0.5 mm and is bonded to the

substrate with a layer of B-stage epoxy 0.15 mm thick.

The epoxy resin, deno ted in the fo llowin g as lid-sub strate

adhesive, contains alumina filler and has a net thermal

conductivity estimated to be 1.5 .

W/m K

Attached to the top of this aluminum lid is a 24.7 ×

27.9 × 15.24 mm aluminum extruded-fin heatsink with

eight extruded fins, as seen in Figure 3. A 50 m thick

layer of thermally conductive epoxy (thermal conduc-

tiveity = ) is used to connect the lid and the

heatsink base and denoted in th e following as TIM2. Ta-

ble 1 displays the assembly dimensions and material

conductivity.

W/m K



2.2. Governing Equations and Boundary

Conditions

The heat diffusion equation is the governing equation for

the temperature of the items in the FC-PBGA/lid/ heat-

sink assembly. For steady state conditions, the heat dif-

fusion equation for this assembly can be written as

xyz

TTT

kkk

xxyyzz



  

 





 



 





g

(1)

where T is the temperature of the item,

 is the heat

dissipation rate per unit volume in the chip and

k are thermal conductivity in the x, y and z directions.

The boundary conditions surrounding the assembly are

heat convection and radiation to the ambient air. The heat

Figure 3. Drawing of the extrude d-fin heatsink.

Table 1. Assembly dimensions and material conductivities

[8].

Item Dimension

(mm) Material Conductivity

(W/m·K)

Chip 7.5 × 5.4 × 0.74 Silicon 109.0

Solder Bump0.127 diameter and

0.0762 height 90/10 Sn/Pb 36

Underfill Epoxy with

silica filler 0.6

Substrate 25 × 25 × 1.0

FR-5 core

material,

4 metal layers,

solder mask on

top and bottom

0.35 for FR-5,

398 for Cu,

0.245 for mask

Solder ball0.77 diameter and

0.45 height 40/60 Sn/Pb 50

PCB

100 × 100 × 1.52,

one top Cu trace

layer (2oz) and

two internal Cu

planes (1oz), with

thermal vias

FR-4 core

material,

4 metal layers,

solder mask on

top and bottom

0.35 for FR-4,

398 for Cu,

0.245 for mask

Extruded-fin

heatsink 24.7 × 27.9 × 15.24 Aluminum 226

loss to the ambient or outward heat flux through the ex-

posed surface is



 

crs

qhhTT



  (2)

in which

T is the assembly surface temperature, T



the ambient air temperature, r is the radiation heat

transfer coefficient and is the convection heat trans-

fer coefficient.

2.3. Finite Element Model

Under forced convection, the convection heat transfer

coefficients c for the FC-PBGA/lid/heatsink assembly

are calculated using the isothermal flat plate correlation

equations previously applied by Mertol [9] as follows.

For the basic FC-PBGA assembly external surfaces,

3.786

hVL, (3)

where V is the airflow velocity in m/s and L is the total

length in the flow direction in meters.

For the heatsink external surface,

4.37

hVL, (4)

where again is airflow velocity in m/s and L is the

average fin length in meters.

Under free convection, the convection heat transfer

coefficient c for the FC-PBGA/lid/heatsink assembly

is calculated as suggested by Ellison [10] for small de-

vices encountered in the electronics industry as

C. F. LIN ET AL.

cch

hfL













, (5)

where

a is the temperature difference in ˚C be-

tween the surface and the ambient air,

T



and are

empirical factors and ch is the package characteristic

length in meters. The constants

and are given as

and for a horizontal plate facing

upward, and for a horizontal plate

facing downward, and and for a

vertical plate. In the equation, ch is the characteristic

length in meters. For horizontal plates,

n

0.83 f

f0.33 n



n

0.415



0.33

1.0.35

ch where and are the re-

spective width and length of a plate. For vertical plates,

, where

LW

LH

LWLWL

is the vertical height of the plate.

When radiating, the radiation heat transfer coefficient

is calculated as







rss

hBfeTTTT



 



, (6)

where B is the Boltzmann constant



5.6710W mKB





, e is the surface emissivity,

f is the radiative view factor,

T is the assembly surface

temperature and is the ambient air temperature.

T

The FC-PBGA/lid/heatsink assembly detailed above is

represented by a three-dimensional finite element model

using ANSYS finite element code. Due to the symmetric

nature of both the heat problem and the assembly, only

one quarter of the assembly is modeled. In the finite ele-

ment analysis, an ambient temperature of 50˚C, and a

uniform chip power dissipation of 3 W is assumed. The

model is complete enough to include key packaging ele-

ments such as bumps, solder balls, substrate, PCB, ex-

truded-fin heatsink, lid, vias, TIM1, TIM2, lid-substrate

adhesive, and ground planes for both signal and power.

2.4. Grid Refinement

Choice of node (or element) density in finite element

solution procedures has a strong effect on the quality and

computational cost. In this paper, variable grid spacing is

used so that a finer spacing occurs in areas of relatively

large gradients. Moreover, a grid dependency study is

performed.

Three finite-element meshes (labeled M1, M2 and M3)

with mesh densities of 168,850, 231,392 and 323,136

elements, respectively, are used to calculate the thermal

resistance of the FC-PBGA/lid/heatsink assembly. The

calculated results are shown in Figure 4 for the cases of

air speeds from 0 to 3 m/sec. Solu tions using meshes M2

and M3 are virtually identical, indicating that M2 is suf-

ficient to obtain reasonable solutions. Mesh M1 seems

too coarse to produce adequate solutions. Since the in-

termediate density mesh M2 requires significantly less

computational effort than the highest density M3, the M2

mesh shown in Figure 5 is chosen as a good trade-off

between accuracy and computational cost.

3. Results and Discussion

The ANSYS three-dimensional finite element analysis of

the thermal characterization in the presented assemblies

yielded the following results.

3.1. Temperature Analysis

The adding of an aluminum lid/heatsink significantly in-

fluences the thermal performance of the assembly. The

temperature contours of the FC-PBGA assembly with-

out/with an aluminum lid/heatsink for an airflow of zero

are shown in Figures 6 and 7, respectively. In Figure 6,

the maximum temperature occurs in the chip. With the

addition of the lid/heatsink, as shown in Figure 7, the

Figure 4. Relation between thermal resistance and airflow

speed for FC-PBGA/lid/heatsink assembly using mesh M1,

M2 and M3.

Figure 5. Finite element mesh M2 used in simulations for

the FC-PBGA/lid/heatsink assembly.

C. F. LIN ET AL. 89

Figure 6. Temperature contours for the basic FC-PBGA as-

sembly at airflow = zero.

Figure 7. Temperature contours for the FC-PBGA/lid/heat-

sink assembly at airflow = zero.

maximum temperature still occurs in the chip. However,

the maximum temperatures drop significantly. The tem-

perature contours of the extruded-fin heatsink are shown

in Figure 8, where the maximum temperature is found at

the bottom center (remembering that the figure shows

only one quarter of the extruded-fin heatsink since the

total assembly is symmetrical), while the minimum tem-

perature occurs at the outside corner of the most distant

fin’s upper edge. The temperature distribution in the ex-

truded-fin heatsink is quite uniform due to the very high

thermal conductivity of the aluminum material.

3.2. Thermal Resistance

As commonly done, thermal resistance



R is used to

characterize the thermal performance of an assembly,

defined as







 (7)

where

T is the predicted maximum temperature for the

assembly, P the device power and is the ambient air

temperature. T

Figure 8. Temperature distribution for the extruded-fin

heatsink at airflow = zero.

For comparison of thermal performance, four different

FC-PBGA assembly versions are considered in this sec-

tion and described as follows:

1) The basic FC-PBGA assembly (or the basic FC-

PBGA model), defined as the FC-PBGA assembly with-

out thermal enhancement shown in Figure 1;

2) Basic FC-PBGA model + lid, defined as the basic

assembly with a lid attached on the top;

3) Basic FC-PBGA model + heatsink, defined as the

basic assembly with a extruded-fin heatsink attached on

the top;

4) Basic FC-PBGA model + lid/heatsink, defined as

the basic assembly with a lid attached on top, after which

extruded-fin heatsink is attached on the top of the lid (i.e.

FC-PBGA/lid/heatsink shown in Figure 2).

Figure 9 shows the thermal performance of the above

four cases for airflows ranging from 0 to 3 m/sec. Addi-

tion of the lid to the basic FC-PBGA model (i.e. basic

FC-PBGA model + lid) causes significant improvement

in thermal performance. The high thermal conductivity

of the aluminum lid results in a larger surface area with a

temperature high enough for good convective cooling.

Addition of only the extruded-fin heatsink to the basic

model (i.e. basic FC-PBGA model + heatsink) causes

large improvement in thermal performance relative to the

basic FC-PBGA model due to the large increase in heat

transfer area. Addition of the lid between the basic FC-

PBGA model and the extruded-fin heatsink (i.e. basic

FC-PBGA model + lid/heatsink or FC-PBGA/lid/heatsink)

results in a small further improvement in thermal per-

formance. This small further increase can be attributed to

the increased cooling area made available by the sides of

the lid. Clearly, the increased cooling area presented by

the sides of lid is small relative to the large total cooling

area of the extruded-fin heatsink. The role of the lid is

interesting. If a extruded-fin heatsink is not applied to the

basic model, then addition of the lid results in significant

C. F. LIN ET AL.

improvement of thermal performance. On the other hand,

if a extruded-fin heatsink has been applied to the basic

FC-PBGA model, then the further addition of the lid

does not result in significant further improvement of

thermal performance.

Inspection of Figure 9 shows that, at an airflow of

zero, the predicted

a of the FC-PBGA/lid/heatsink is

about 57.0% lower than the basic PBGA assembly. If

progressively faster air flow is applied to the FC-PBGA/

lid/heatsink, then the improvement of the FC-PBGA/lid/

heatsink relative to the basic FC-PBGA assembly at air-

flow = zero increases with increasing air speed, reaching

a maximum improvement of 84.9% at this study’s

maximum airspeed of 3 m/s.

3.3. Effects of Design Parameters

Thermal performance is analyzed by considering various

design parameters of the polymer-based materials and the

thermal enhancement components. The polymer-based

materials include underfill, TIM1, TIM2, lid-substrate

adhesive and substrate core material. The specific ther-

mal enhancement components are the lid and the ex-

truded-fin heatsink. Effects of the design parameters are

studied by varying the parameter values by 30% for all

material conductivities and by 15% for all material di-

mensions in both natural and forced convection

environments. Simulation results are shown in

Figures 10-13.



0v





1v

Figure 9. Relation between thermal resistance and airflow

speed for four different assembly configur ations.

Figure 10. Relation between thermal resistance and thermal

conductivity in natural convection condition





Figure 11. Relation between thermal resistance and thermal

conductivity in forced convection condition .



1v

3.3.1. Effect of Extruded-Fin Heatsink

Extruded-fin heatsink design has significant effect on

thermal performance of the assembly. The effects of ex-

truded-fin heatsink conductivity with regard to thermal

performance of the assembly can be found in Figures 10

and 11 for both natural and forced convection environ-

ments, respectively. Increased extruded-fin heatsink

conductivity increases the thermal performance of the

assembly since higher thermal conductivity improves the

heat spreading effect in the heatsink. Figure 14 further

shows the thermal resistance

a vs the thermal con-

ductivity of the extruded-fin heatsink for airflows rang-

ing from 0 to 3 m/sec. The results show little improve-

ment in performance at thermal conductivities above

200 WmK



. Thus, little advantage can be obtained by

using copper (thermal conductivity = 393 W/m·K) rela-

tive to aluminum (thermal conductivity = 226 W/m·K).

C. F. LIN ET AL. 91

Figure 12. Relation between thermal resistance and dimen-

sions in natural convection condition .



0v

Figure 13. Relation between thermal resistance and dimen-

sions in forced convection condition .



1v

Figure 14. Relation between thermal resistance and extru-

ded-fin heatsink conductivity.

This observation is of interest to designers with regard to

material selection.

Effects of fin length, fin thickness, fin number and base

thickness of the extruded-fin heatsink on thermal resis-

tance

a are presented for the FC-PBGA/lid/heatsink

assembly. Increasing the number of fins or the length of

the fins decreases the thermal resistance

a due to the

increase of heatsink cooling area, as shown in Figures 15

and 16 , for both natural





0v and forced convection







environments.

It is seen that

a improves as the base thickness in-

creases because increased base thickness increases the

total cooling area of the heatsink and improves the cool-

ing efficiency of the heatsink. But the improvement is

small and the resulting material cost could be higher.

Figure 15. Relation between thermal resistance and design

parameters of extruded-fin heatsink in natural convection

condition







Figure 16. Relation between thermal resistance and design

parameters of extruded-fin heatsink in forced convection

condition







C. F. LIN ET AL.

Increasi fing the n thickness increases the total cooling

rotect the chip and improve heat

ea of the heatsink. However this increased cooling area

is very small compared with the total area of the heat-

sink, so the results show only a slight effect for fin thick-

ness and can be neglected.

3.3.2. Effect of the Lid

The purpose of lid is to p

spreading from the chip. Effect of thermal conductivity

of the lid on the thermal performance of the assembly for

both natural and forced convection environments can

also be found in Figures 10 and 11, respectively. In-

creased lid conductivity increases the thermal perform-

ance of the assembly.

Specific variance of the thermal resistance

2 a rela-

tive to the lid thickness is shown in Figures 1nd 13

for both natural and forced convection environments.

The results shows a small improvement in

R as thick-

ness increases.

3.3.3. Effect of Underfill fill is to release the thermo-

M2 the thermal perform-

the substrate

e assembly due to a longer thermal path

ffect of Lid-Substrate Adhesive

An adhesive material is required to form a good bond

cts of the con-

finite element simulation has been

thermal performance of a thermally

gn parameters of the polymer-

mal performance of the assembly. High er ther-

The purpose of the under

mechanical stress of the solder bumps due to CTE mis-

match between the silicon chip and the organic substrate.

Increased thermal conductivity of the underfill increases

the heat conduction in the package and is helpful for dis-

sipating heat to the ambient atmosphere. Thus, increasing

the conductivity of the underfill increases the thermal

performance of the assembly.

3.3.4. Effect of TIM1 and TI

The effects of TIM1 and TIM2 on

ance of the asse mbly for both natura l and forced convec-

tion environments can also be found in Figures 10-13.

As TIM1’s or TIM2’s conductivity incr eases, the ther-

mal performance of the assembly increases, since in-

creased conductivity of TIM1 or TIM2 reduces the ther-

mal resistance in the heat transfer path. Also, it can be

found in Figures 12 and 13 that as TIM1’s or TIM2’s

thickness decreases, the thermal performance of the as-

sembly increases, since decreased thickness of TIM1 or

TIM2 reduces the thermal resistance in the heat transfer

path. Simulation results show that TIM1 has a greater

influence on assembly thermal performance than TIM2.

3.3.5. Effect of Substrate Core Material

The effect of the thermal conductivity of

core material on the thermal performance of the assem-

bly can also be found in Figures 10 and 11. Increasing

the conductivity of the substrate core material increases

heat transfer from chip to ambient, but the amount of

heat conducted through this pathway is quite small rela-

tive to the amount conducted through the vias and heat-

sink. Thus, thermal performance increases with increas-

ing conductivity of the substrate core material, but the

effect is small.

Thicker substrate core material reduces the thermal

performance of th

r heat transfer to the PCB. Thus thermal performance

decreases with increasing thickness of the substrate core

material but the effect is small, as seen in Figures 12 and

13.

3.3.6. E

between the lid and the substrate. The effe

ductivity and thickness of the adhesive with regard to the

thermal performance of the assembly are also shown in

Figures 10-13. It is found that these effects are all rela-

tively insignificant, but higher conductivity and smaller

thickness are preferred.

4. Conclusions

Three-dimensional

used to study the

enhanced FC-PBGA assembly in both natural and forced

air convection environments. The thermally enhanced

FC-PBGA assembly is a basic FC-PBGA assembly with

a lid attached on top, after which an extruded-fin heat-

sink is attached on the top of the lid. The adding of an

aluminum lid/heatsink significantly influences the ther-

mal performance of the assembly due to the large in-

crease in heat transfer area. Also, the temperature dis-

tribution in the extruded-fin heatsink is quite uniform due

to the very high thermal conductivity of the aluminum

material. If a extruded-fin heatsink is not applied to the

basic model, then addition of the lid results in significant

improvement of the thermal performance. On the other

hand, if an extruded-fin heatsink has been applied to the

basic model, then further addition of the lid does not re-

sult in significant further improvement of thermal per-

formance, because the increased cooling area presented

by the sides of lid is little relative to the large total cool-

ing area of the heatsink.

A series of parametric simulations investigate the ef-

fects of varying the desi

sed materials and the thermal enhancement compo-

nents. Conclusions from the analysis are summarized as

follows:

1) Extruded-fin heatsink design has significant effects

on the ther

al conductivity improves the thermal performance of

the assembly. However, results show little improvement

in performance at thermal conductivities above 200

W/m·K. Thus, little advantage can be obtained by using

copper (thermal conductivity = 393 W/m·K) relative to

aluminum (thermal conductivity = 226 W/m·K). This

observation is of interest to designers with regard to ma-

C. F. LIN ET AL.

or TIM2 decreases, the thermal

s but the improve-

ce of the assembly increa-

nd to have lesser impact o

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base thickness of the extruded-fin heatsink results in in-

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cases studied, simulation results show that the fin length

and fin number have a stronger influence on the thermal

performance than base thickness. The effect of fin thick-

ness is negligibly small.

2) As for conductivity, when TIM1 or TIM2 increases

or the thickn ess of TIM1

rformance of the assembly increases. Simulation re-

sults show that TIM1 has a stronger influence on assem-

bly thermal performance than TIM2.

3) As conductivity of the underfill increases, thermal

performance of the assembly increase

ent is not very significant.

4) It is found that as the thickness of the substrate core

decreases, thermal performan

s. Thermal performance of the assembly can be en-

hanced by using a thinner core. Also, higher conductivity

of the substrate core is desirable for better thermal per-

formance of the assembly.

5) The effects of the lid-substrate adhesive parameters

are also considered and foun

ckage thermal performance. However, higher conduc-

tivity and lower thickness of the lid-substrate adhesive

are found preferable.

. Ju and T. C. Tsein, “

t Analysis of Thermom

in Flip-Chip Packages under Temperature Cycling Condi-

tions,” Journal of Reinforced Plastics and Composites,

Vol. 24, No. 18, 2005, pp. 1895-1907.

doi:10.1177/0731684405054333

[2] F. Gugliermermetti and S. Grignaffini, “Direct Approach

Thermal performance of Flip Chip Ball Grid

hiang, “Thermal

to the Design of Plate Fin Heat Sinks Stack Cooled by

Forced Convection,” IEEE Electronic Packaging Tech-

nology Conference, San Diego, 8-10 December 1998, pp.

138-142.

[3] B. Joiner, “

Arrays Packages,” Eighteenth Annual IEEE Semiconduc-

tor Thermal Measurement and Management Symposium,

San Jose, 12-14 March 2002, pp. 50-56.

[4] K. M. Chen, K. H. Houng and K. N. C

Resistance Analysis and Validation of Flip Chip PBGA

Packages,” Microelectronics Reliability, Vol. 46, No. 2-4,

2006, pp. 440-448. doi:10.1016/j.microrel.2005.06.001

[5] Z. Luo, H. Cho and K. Cho, “System Thermal Analysis of

Mobile Phone,” Applied Thermal Engineering, Vol. 28,

No. 14-15, 2008, pp. 1889-1895.

doi:10.1016/j.applthermaleng.2007.11.025

[6] A. R. Menon, S. Karajgikar and D. Agonafer, “Thermal

evision 13.0,” Swanson Ana-

ermal Enhancement on

Design Optimization of a Package on Package,” 25th

Annual IEEE Semiconductor Thermal Measurement and

Management Symposium (Semi-Therm), San Jose, 15-19

March 2009, pp. 329-336.

[7] “ANSYS User’s Manual, R

lysis System Inc., Houston, 2010.

[8] T.-Y. Lee, “An Investigation of Th

Flip Chip Plastic BGA Packages Using CFD Tool,” IEEE

Transactions on Components, Packaging, and Manufac-

turing Technology, Vol. 23, No. 3, 2000, pp. 481-489.

doi:10.1109/6144.868847

[9] A. Mertol, “Thermal Performance Comparison of High

tations for Electronic Equip-

omenclature

Pin Count Cavity-Up Enhanced Plastic Ball Grid Array

(EPBGA) Packages,” IEEE Transactions on Components,

Packaging, and Manufacturing Technology, Part B, Vol.

19, No. 2, 1996, pp. 427-443.

[10] G. N. Ellison, “Thermal Compu

ment,” E. Robert Krieger Publishing Company, Malabar,

1989.

Nn: empirical factor.

P:it bd.

device power, W.

: empirical factor. ll grid array. PCB: printed circuoar

FC-PBGA: flip-chip plastic ba





: temperature difference between the surface and

: heat dissipation rate per unit volume in the chip, the ambient air, ˚C.



: ambient air tem

3. Wm

kperature, ˚C.

: thermal conductivity, WmK.

k: thermal conductivity in the x direction, WmK



k: thermal conductivity in the y direction, WmK



k: thermal conductivity in the z direction, WmK



h: convection heat transfer coefficient, 2

Wm K



rad : radiation heat transfer coefficient, h2

Wm K



L: characteristic length, m.

R: thermal resistance of the assembly, ˚C/W.

temperature, ˚C.

C. : predicted maximum temperature of an assembly,

˚: surface temperature of the assembly, ˚C.

V: air velocity, m/s.