Determination Of Fracture Toughness In PBGA Packages Using Finite Element And Experimental Methods

DETERMINATION OF FRACTURE TOUGHNESS IN PBGA PACKAGES USING FINITE ELEMENT AND

EXPERIMENTAL METHODS

by

TAN CHEW PHENG

Thesis submitted in fulfillment of the

requirements

for the

degree

^of

Master of Science

U.S.M, Penang

November 2006

14,976 Words

,\'�t1"wkd!;CI1lCI1I'

ACKNOWLEDGEMENTS

I would like to express my

appreciation

^{and thanks to} my supervisor Assoc. Prof. Dr. Ishak

Hj.

Abdul Azid and my

co-supervisor,

^{Assoc. Prof Dr}

Mani Maran for their

grateful support, encouragement

^{and invaluable}

guidance

in

helping

^{me to} cope in every

stage

^{of the}

project

I also wish to thank _my friends from the School of Mechanical

Engineering,

^{Universiti Sains}

Malaysia especially

^Mr.

Ong Kang

^{Eu and Mr}

Lee Boon

Leong

^{for their}

help

^{in this}

project.

^I also wish to thank Prof. K. N Seetharamu and Prof. M. V. V.

Murthy

^{for their}

guidance during

^the

early

stage of this

project.

I would like to thank every ^lab staff of the School of Mechanical

Engineering especially

^{Mr. Baharom B.}

Awang

and Mr. Md. Ashamuddin Hasim for their technical

support during

my

experiments

^{for this} project I also would like to thank Mr. Md. Zandar Md. Saman from the School of Materials & Minerai

Resources

Engineering

ⁱⁿ

providing

^materials.

Finally,

^{I wish to} thank my

family

^members for their moral support

especially

^my

parents.

Thanks also to those who

helped

^{me either}

directly

^or

indirectly

ⁱⁿ

completing

^my

project.

1,\1\ ('lIEWr/lENG McchFI1�.^{US1\(()(" �} 11 ^-

Tableofcontents

TABLE ,,)F CONTENTS

Page

Acknowledgements

^II

Table of Contents III

List of Tables VIII

List of

Figures

^X

List of Plates xv

List of Abbreviations ^XVI

List of

Symbols

^XIX

List of

Equations

^xxv

Abstrak ^XXXI

Abstract ^XXXIII

CHAPTER 1 ^- INTRODUCTION ^1-6

1.1

Background

^{of research 1}

1.2 Problem statement 3

1.3

Objectives

⁴

1.4

Scope

of research ⁵

CHAPTER 2 ^- LITERATURE REVIEW ^7-21

2.1 Introduction ⁷

2.2 Review of related research on vapor pressure effect ⁷

2.3 Review of fracture

toughness analysis techniques

¹⁰

2.4 Review of related research on fracture

toughness

^{method 15}

2.5 Review ^on

holographic interferometry techniques

¹⁸

TAN cutw PHENGMcchEng,^{USM 0(,' - III -}

Table ofcontents

2.6 Review of

holographic technique applied

for fracture

toughness

¹⁹

2.7

Summary

²⁰

CHAPTER 3 ^- ANALYSIS OF STRESS INTENSITY FACTOR IN 22-50 PLASTIC BALL GRID ARRAY

(PBGA)

3.1 Introduction 22

3.2 Theoretical

applications

^{of MCCI method 24}

3.3 Methods of measurement 26

3.4

Methodology

²⁹

3.5 Verification on Meei method 32-36

3.5.1 Thin

quad

^flat

package

^{finite element}

modeling

³²

3.5.2

Sample

calculation on strain energy ^{release rate 35}

3.5.3 Results and discussions 36

3.6 Simulations and calculations 37-43

3.6.1

Temperature

distribution 37

3.6.2 Moisture distribution 39

3.6.3

Vapor

pressure determination ⁴³

3.7 Results and discussions 44-49

3.7.1

Sample

calculation on strain energy ^{release rate 45} 3.7.2

Sample

calculation on stress

intensity

^{factor 45}

3.7.3 Results and discussions ⁴⁷

3.8

Summary

⁴⁹

CHAPTER 4^- DETERMINATION OF FRACTURE TOUGHNESS 51-76 USING SIMULATION AND CONVENTIONAL TENSILE TEST

4.1 Introduction 51

4.2

Underlying

^{theories offracture}

toughness

^{test 53-59}

TAN CIIEWPlIENG McchEng.^{USM 06' - IV -}

Table()fcontents

4.2.1

Theory

of fracture

toughness

⁵³

4.2.2 Fracture

toughness for single edge

notched tension 55

4.3

Sample specifications

⁶⁰

4.4 Simulation evaluation 61-69

4.4.1

Ansys

^{simulation on thin}

plate

deformation 6'1

4.4.2 Parameter

study

⁶²

4.4.3 Discussions 68

4.4.4

Epoxy

^based

polymer

^thin

plate

^{evaluation 69}

4.5 Conventional tensile test evaluation 70-74

4.5.1 Procedures oftest 70

4.5.2 Results and discussions 70

4.6

Summary

⁷⁵

CHAPTER 5 ^- DETERMINATION OF FRACTURE TOUGHNESS 77 -118 USING HOLOGRAPHIC INTERFEROMETRY METHOD

5.1 Introduction 77

5.2

Underlying

^{theories of real-time}

holographic interferometry

⁷⁹

5.3

Methodology

^82-89

5.3.1

Optical system

^for

holographic

measurement 82

5.3.2

Layout specifications

⁸⁴

5.3.3

Expanding

^{beam with}

spatial

^{filter 85}

5.3.4 Beam

intensity

^{ratio 86}

5.3.5

Optical stability

^{test 87}

5.3.6

Exposure

^time

during image recording

⁸⁸

5.3.7

Hologram image processing

⁸⁸

5.4

Holographic interferometry

calibration ^89-102

IAN CHEWPIlENGMcchEng.^{USM06' - V-}

Tableoi"contents

5.4.1 Cantilever evaluation 89

5.4.2 Strain energy ^for linear deflection 94

5.4.3

Measuring fringe

^{order number 95}

5.4.4

Perspective

^{distortion 97}

5.4.S

Sample

calculations 98

5.4.6 Results and discussions 101

5.5 Uniform axial load evaluation

using holographic interferometry

^103-114

5.5.1 Mathematical

application

¹⁰³

S.S.2

Correcting

^{errors in}

holographic

^fracture

toughness

^{test 104}

5.S.3

Holographic

^fracture

toughness

^test for aluminum 106 5.5.4

Holographic

^fracture

toughness

test for epoxy 110

5.6 Results and discussions 114

S.7

Types

^{of error}

during holographic interferometry

¹¹⁵

S.8

Summary

¹¹⁸

CHAPTER 6 ^- CONCLUSIONS AND RECOMMENDATIONS ^119-121

6.1 Conclusions 119

6.2 Recommendations and futurework 121

References 122-127

1 ^.

2.

Ansys

^simulation program code for TQFP

plastic

deformation

Ansys

simulation program code for PBGA

temperature

distribution

Ansys

^simulation program ^COC9 for PBGA wetness distribution

Ansys

^simulation program code for PBGA

plastic

deformation

128-213

128

135

Appendices

3.

4.

145

155

T /\NCIIEWPHENG MechEng.^{USM 06' -} VI ^-

Tableof^contents

5.

Ansys

^simulation program code for ^thin

plate

deformation 164 6.

Ansys

^{simulation on aluminum}

plate

^{in different crack ratio 168}

7. Simulation

analyses

^{on thin}

plate

^fracture

toughness

¹⁷²

8. Cantilever deflection

using holographic interferometry

^{method 176}

9. Aluminum

plate

^extension

using holographic interferometry

¹⁹²

method

10.

Epoxy plate

^extension

using holographic interferometry

method ²⁰⁴

Publication List

I.A.

Azid,

^{C.P. Tan. B.L.}

Lee,

^{K.N. Seetharamu}

(2005).

Fracture Mechanic

Analysis

^for

Package

Delamination.

Key Engineering Materials,

Vols.297-300.

p.844-850.

TANCHEWPHENGMechEng.^{USM 06' - VU -}

Listoftables

LIST OF TABLES

Page

Table 3.1 Dimensions of PBGA 23

Table 3.2 Material

properties

^forthe main constituents of PBGA 23 Table 3.3 Shear modulus for interfacial delamination stress 24

intensity

^factor

Table 3.4 Mathematical

applications

^of

experimental

^{methods 29} Table 3.5

Analogy

^{between thermal} and moisture 29

Table 3.6 Dimensions ofTQFP 33

Table 3.7 Material

properties

for the main constituents ofTQFP 33 Table 3.8

Comparison

^{MCGI method with}

Park,

^{Y.B. et als 36}

results for 1 MPa vapor pressure

Table 3.9 Thermal

properties

^{for PBGA 37}

Table 3.10 Moisture

properties

^{for PBGA}

(85°C/85%RH)

³⁹

Table 4.1 Material

properties

^for

AI, Cu,

MS and epoxy ^{resins 51} Table 4.2 The

specifications

^{and its}

plane

^{condition 60}

Table 4.3 Critical load and

compliance

^{rate for}

AI,

^{Cu and MS 73}

Table 4.4 Fracture

toughness

^{used total extension for}

AI,

^{eu and 74}

MS

Table

5.1(a) Compositions

^of chemical for solution A 88 Table

5.1(b) Compositions

of chemical for solution B 88 Table

5.1(c) Compositions

^{of chemical for} bleach solution 88 Table 5.2 Values of deflection for

6�m deflection, 6:r

^{delivered 99}

theoretically

Table 5.3 Coordinates of

point

^{a, b and c 100}

TAN CHEWPHENG McchEng.^{USM 06' -} Vl11 ^-

l.istoftables

Table 5.4 Deflections obtained

experimentally

^{in case}

study

^{1 100} Table 5.5 Deflections obtained

experimentally

^{in case}

study

^{2 101} Table 5.6 Extension

along

^AI

plate,

2.45mm crack

length

^{loaded 107}

with 4N

using

^{HI method}

Table 5.7 Material

properties

for D.E.R. 331 cured with Ancamide 110 260A

Table 5.8 Extension

along

epoxy

plate,

^{1mm crack}

length

^{loaded 112}

with 1 N

using

^{HI method}

TANCIIEWPHENG McchEng,^{USM 06' - IX-}

l.rstoffigures

LIST OF FIGURES

Page

Figure

^{1.1 I R reflow}

soldering profile

²

Figure

^{1.2 Plastic}

collapse

of popcorn failure ⁴

Figure

^2.1

Cracking

^mechanism

during

^reflow

soldering

⁸

Figure

^{2.2 Cracked}

body subjected

^{to load F 10}

Figure

^2.3 Load-extension

diagram

¹¹

Figure

^{2.4 SENB for K} determination 13

Figure

^{2.5 CT for K} determination ¹⁴

Figure

^{2.6 I}nteriacial fracture

toug

^{hness test 14}

Figure

^{2.7 Schematic}

diagram

of adhesion test 16

Figure

^{2.8 Generic}

interferometry

^{model 18}

Figure

^3.1 Schematic of X PBGA 22

Figure

^{3.2 The}

principle

^of

superposition

²⁸

Figure

^{3.3 The}

spectrum

^of

experimental

^methods

applied

^{on 28}

fracture

problems

Figure

^{3.4 Crack}

tip

^{elements 31}

Figure

^3.5 Cross sectional view ofTQFP ³³

Figure

^3.6

Typical plastic

deformation in TOFP 34

Figure

^3.7 Plastic deformation in TQFP

(x1 00)

³⁵

Figure

^3.8 Variation of SERR with delamination ratio for TQFP 36

using

MCCI method at different vapor pressure

loadings

Figure

^3.9

Temperature

distribution on PBGA

during

^{reflow 38}

Figure

^{3.10 Case}

study

^on

temperature

distribution for LEO 39

TANCHEWPHENG McchEng.USM 06' ^- X ^-

LI�lofligures

Figure

^{3.11 Transientwetness} distribution in PBGA for 34 hours 40

Figure

^3.12 Transient wetness distribution in PBGA for 168 41 hours

Figure 3.13(a)

Transient wetness distribution in LED for 34 hours 42

Figure 3.13(b)

Transient wetness distribution in LED for 168 hours 42

Figure

^3.14

Typical plastic

deformation in PBGA 44

Figure

^3.15 Plastic deformation in PBGA

(x1 000)

⁴⁵

Figure 3.16(a)

Variation of SERR with delamination ratio for PBGA 47

Figure 3.16(b)

Variation of SIF with delamination ratio for PBGA 47

Figure 3.17(a)

^{Variation of SERR} with vapor pressure for PBGA 48

Figure 3.17(b)

^{Variation of} SIF with vapor pressure for PBGA ⁴⁸

Figure

^{4.1 3-D}

drawing

^{of thin}

plate specimen

⁵²

Figure

^4.2 Conventional tensile test 52

Figure

^{4.3 Fracture}

toughness

^with thickness for steel 54

(rr, =2068.43MPa)

Figure

^4.4 Linear elastic thin

plate

⁵⁵

Figure

^{4.5 Plate su}

bjected

^{with a load 55}

Figure

^{4.6 Free}

body diagram

^{of thin}

plate

^{in left}

portion

⁵⁷

Figure

^{4.7 AI}

plate

deformation with crack ratio 0.1

(x100)

⁶¹

Figure 4.8(a)

^Variation of fracture

toughness

^{with crack}

length

⁶²

ratio on total extension and crack

edge

^{extension for}

AI

Figure 4.8(b)

^Variation of fracture

toughness

^{with total}

plate length

⁶³

for AI

Figure 4.8(c)

^Variation of fracture

toughness

^with

plate

^{thickness 63}

for AI

Figure 4.8(d)

^Variation of fracture

toughness

^with

applied

^{load for 64}

AI

T ANCHEW PHENG MechEng.^{USM06' -} Xl ^-

l.ist oi"figures

Figure 4.9(a)

^{Variation offracture}

toughness

^{with crack}

length

⁶⁴

ratio on total extension and crack

edge

extension for eu

Figure 4.9(b)

Variation offracture

toughness

^{with total}

plate length

⁶⁵ for Cu

Figure 4.9(c)

Variation of fracture

toughness

^with

plate

^{thickness 65}

for Cu

Figure 4.9(d)

Variation of fracture

toughness

^with

applied

^{load for 66}

eu

Figure

^4.1

O(a)

^Variation of fracture

toughness

^{with crack}

length

⁶⁶

ratio on total extension and crack

edge

extension for MS

Figure 4.10(b)

Variation of fracture

toughness

^{with total}

plate length

⁶⁷

for MS

Figure

^4.1

O(c)

Variation of fracture

toughness

^with

plate

^{thickness 67}

for MS

Figure

^4.1

O(d)

Variation offracture

toughness

^with

applied

^{load for 68}

MS

Figure

^4.11 Variation of fracture

toughness

^{with crack}

length

⁶⁹

ratio for _epoxy

Figure 4.12(a)

^Total extension-load curve for AI 71

Figure 4.12(b)

^{Variation of}

compliance

^{with crack}

length

^{ratio for AI 71}

Figure 4.13(a)

Total extension-load curve for eu 72

Figure 4.13(b)

^{Variation of}

compliance

^{with crack}

length

ratio for eu 72

Figure 4.14(a)

Total extension-load curve for MS ⁷³

Figure 4.14(b)

Variation of

compliance

^{with crack}

length

^{ratio for 73}

MS

Figure

^5.1 Load-extension mechanism 78

Figure

^5.2 Path of incident and reflected _rays at

point

^{b 80}

Figure

^5.3 3-D reflected ray ^at

point

^{o 80}

Figure

^5.4

Optical system

^{for HI} measurement 83

TANClIEWI'll[NG McchEng.^{USM06' - XII}

-

List offigures

Figure

^5.5

Optical layout

^{with its}

specifications

⁸⁴

Figure

^5.6

Optical system

^for

stability

^{test 87}

Figure

^{5.7 Cantilever deflected in an}

angle, ¢

⁹⁰

Figure

^5.8 Illumination and observation

angle

^{in x- z}

plane

⁹¹

Figure

^5.9 Cantilever rotate into an

angle, /3

⁹³

Figure

^{5.10 Free}

body diagram

of cantilever with

applied load,

^{F 94}

Figure

^{5.11 Line}

profile

^of

fringes pattern

^for cantilever deflection 96

Figure

^5.12

Comparison

^{of unit}

pixel

^{and unit} dimension in the 97

analysis

^of

perspective

^distortion

Figure

^5.13

Ansys

^{simulation on} cantilever deflection

(x200)

^{for 99}

Bum deflection, oZF

Figure 5.14(a) Comparison

^of

holographic

result with deflection 101

theory

^for cantilever in

0ZF =6�m

Figure 5.14(b) Comparison

^of

holographic

result with deflection 102

.

theory

^for cantilever in

au

⁼¹

Ourn

Figure 5.14(c) Comparison

^of

holographic

result with deflection 102

theory

for cantilever in

au

⁼

14J.lm

Figure 5.15(a)

^Extension distribution

along plate using

^{HI method 105}

Figure 5.15(b)

^Extension distribution

along plate using Ansys

¹⁰⁵

simulation

Figure

^5.16

Correcting

^{errors in}

holographic analysis

¹⁰⁶

Figure

^5.17 Load-extension curve for AI

plate

^{with crack}

length,

¹⁰⁶

as=

^4mm

Figure

^{5.18 Line}

profile

^of

fringes pattern

^{for AI}

plate,

^{2.45mm 107}

crack

length

loaded with 4N

Figure

^5.19 Extension distribution

along

^AI

plate

¹⁰⁸

Figure

^{5.20 Strain at center crack in different}

loading

^{for AI}

plate

¹⁰⁸

Figure

^5.21 Variation of

compliance

^{with crack}

length

^{ratio for AI 109}

plate

IANcur.w1'1I[,NG MeehEng.^{USM 06' - Xlll -}

l.istoffigures

Figure

^5.22 Load-extension curve for D.E.R. 331 with crack ¹¹¹

length,

as⁼ 4.5mm

Figure

^{5.23 Line}

profile

^of

fringes pattern

for epoxy

plate,

^{1mm 112}

crack

length

loaded with 1N

Figure

^{5.24 Extension} distribution

along

epoxy

plate

¹¹²

Figure

^{5.25 Strain at center crack in different}

loading

for epoxy ¹¹³

plate

Figure

^{5.26 Variation of}

compliance

^{with crack}

length

^{ratio for 113}

epoxy

plate

Figure

^5.27

Safety

conditions for EMC

(O.E.R. 331)

^{on PBGA 114}

TANCHEW PHENG McchEng.^{USM 06'}

- XIV ^-

list ofplates

LIST OF PLATES

Page

Plate 5.1 Illustration of load frame 79

Plate 5.2 Real-time

interferometry set-up

for cantilever evaluation 83

Plate 5.3 Cantilever beam 90

Plate

5.4(a)

^Cantilever

image

⁹⁶

Plate

5.4(b)

^Initial

fringes pattern

⁹⁶

Plate

5.4(c)

^Loaded

fringes pattern,

^case

study

^{1 96}

Plate

5.4(d)

^Loaded

fringes pattern,

^case

study

^{2 96}

Plate 5.5

Graph

paper ^as

rectangular grid pattern

^{on cantilever 97}

beam

during analysis

^of

perspective

^distortion

Plate 5.6

Fringes pattern

^{for AI}

plate,

^{2.45mm crack}

length

^{loaded 107}

with 4N

Plate 5.7

Fringes pattern

for epoxy

plate,

^{1mm crack}

length

¹¹¹

loaded with 1N

Plate

5.8(a) Hologram

^with

fringes

ⁱⁿ its initial condition 117 Plate

S.8(b) Hologram

^with

fringes

ⁱⁿ its initial condition 117

TANCHEW PHENG^MechEng.^{USM06' - XV -}

List ofabbreviations

LIST OF ABBREVIATIONS

Page

1-0 One-dimensional 8

2-D Two-dimensional

8,20,22,25-28

3-D Three-dimensional

20,26,28,52,78-92,121

Ag

^{Silver 23}

AI Aluminum

51,60-64,

70-77,104-109

Anhyd. Anhydrides

⁸⁸

ASTM American

Society

^for

Testing

^{and Materials 55}

8S1 British Standards Institute 55

BT Bismaleimidetriazine

22,23,37

^-40

CCD

Charge-coupled

^device

83,95

CI Conventional

interferometry

¹⁹

C-SAM C-mode

scanning

^acoustic

microscopy

⁸

CPU Central

processing

^{unit 83}

CTE Coefficient of thermal

expansion 15,17

Cu

Copper 17,24,51,60-66,70-75

O.E.R Dow epoxy resins

(trademark

^{ofthe Dow}

49,77,110-121

Chemical

Company)

OHI

Digital holography interferometry 19,20

EMC

Epoxy molding compound

^1-6,

16,23,30�34,

77,114-121

ESPI Electronic

speckle pattern interferometry

¹⁹

FE Finite element

3,9,25,30,78

TANCHEW PHENG McchEng,^{USM06' - XVI -}

List ofabbrevintions

FEA Finite element

analysis 4,9121-23,29,34,35.40, 45,49,52,59,119,121

FEM Finite element method 18,25,26

GI

Grating (moire) interferometry

¹⁹

HI

Holographic interferometry 4-7,18-21,68,74-89,

98-107,111-121

IC

Integrated

^circuit

1,8,9,17

IR InfraRed 1

JEDEC Joint Electron Device

Engineering

^{Council 40}

LED

Lig

^ht

emitting

^diode

38,39,41,42

LEFM Linear elastic fracture mechanics 15.25,69

MGGI Modified crack closure

integral 5,24,26,30- 32,36,49,119,121

NOT Non-destructive test 18

PBGA Plastic ball

grid

array

2-8,22,23,36-49.

77,114-120

PCB Printed circuit board

22,23,37

^-39

PQFP Plastic

quad

^flat

package

⁵³

QFN Quad flat non-lead 9

RH Relative

humidity 5,22,40-43

SERR Strain energy release rate

4,15-17,22-27,30, 35,36,45-49,58

Si Silicon

23,33

SiC Silicon carbide ⁴⁹

SIF Stress

intensity

^factor

4-6,13-17,22-31,

46-53,59,114,118-121

SMD Surface mount device ⁷

SMT Surface mount

technology

^1,15

TANCHEW PH ENG McchEng,^{USM 06' -} XVll ^-

Listof abbreviations

SOJ

TQFP

VPR

Small outline J-Ieaded

Thin

quad

^flat

package Vapor phase

^reflow

TANCHEW PHENG MechEng,^{USM 06'}

40,43 5,15,16,32-36,49

1,9

- XVlll ^-

List of syrnbo!s

LIST OF SYMBOLS

Page

t;

^Reflow

soldering temperature (OC)

²

Ix

Soldering

^time

(s)

²

as Control

sample's

^crack

length (m) 6,70-73,106-113

t Thickness

(m) 10-15,26-35,45,52-69

78,95,98,109,114

F

Applied

^load

(N) 10-14,31,35,45,52-73,

94-99,105-113

8 Crack

edge

^extension

(m) 10-12,55-62,108,112

a Crack

length (m) 10-14,25,26,31-36,

45-73,78,109-114

W

Sample

^width

(m) 10-15,52-73,78,

95,98,109-114

G Strain energy release rate

(J/m2) 11,12,25,26

U Stored strain energy

(J) 11,12,56,57

C

Compliance,

^the

slope

of extension-load

12,71-73,108-114 (mIN)

Ke

Critical stress

intensity

^factor

(MPa

^m

1/2) 12-17,49-54,59- 69,74,1

09,¹¹⁴

Ge

^Critical strain energy release rate

(J/m2) 12,15,58,59

E

Young's

^modulus

(GPa) 12,15,23,26,32,33,46,

51-73,94,98,109-114

Fe

^Critical

loading (N) 12-15,58,59,

70-74,106-114

L

Length

^distance

(m) 13-15,33,52-69,90-113

S Distance between two

pin support (m)

¹³

K Stress

intensity

^factor

(MPa

^m

1/2) 13,14,28

TANCHEW PHENGMcchEng,^{USM 06' - X1X -}

Li,1 ofsymbols

Moment inertia of

multilayer (dimensionless)

¹⁵

E" Effective

Young's

^modulus

(GPa) 15,32,46

Jr Pi

(=3.142) 15,25,31,32,46

f2 Bimaterial constant

(dimensionless) 15,31.32,46

J Crack

driving force,

^J

integral (J/m2) 15,16,27,32.49,53 KJI

^{Mode II stress}

intensity

^factor

(MPa

^m

1/2) 16,26

KlIC

Critical mode II stress

intensity

^factor

(MPa

¹⁶

m

1/2)

v Poisson's ratio

(dimensionless) 23,32,33,45, 46,51,62-73

ji Shear modulus

(GPa) 24,31,32,45,46

ljI Work ofthe external tractions per ^{unit 25} thickness

(Jim)

Strain energy of the

body

per unit thickness ²⁵

(jim)

Normal stress

(N/m2) 25,29,56

r Shear stress

(N/m2) 25,29

v

Opening displacement

^{on crack surfaces}

(m) 25,26,29,31,35,45

u

Sliding displacement

^{on crack surfaces}

(m) 25,26,29 GI

^{Mode I} strain energy release rate

(J/m2) 26,31-36,45-48 G"

^{Mode II strain energy} release rate

(J/m2)

²⁶

KI

^{Mode I stress}

intensity

^factor

(MPa

^m

1/2) 26,32,46-49,114

TJ

Multiplier depending

^{Poisson's ratio u and}

26,46,59 geometry (dimensionless)

77⁼

1/(I-u2)

^for

plane strain;

^{17;:: l for}

plane

stress

�.

Normal force

(N)

²⁶

Fe

Shear force

(N)

²⁶

T AN CHEWPHENGMcchEng,^{USM 06' -} XX-

Li51ofsymbols

o

Strain energy

density (J/m3)

²⁷

T Traction vector

(N/m2)

²⁷

u

Displacement

^vector

(m)

²⁷

ds Element of arc

length

^around the contour r 27

(m)

r Contour in crack

driving

^{force 27}

(dimensionless)

N

Fringe

order number

(dimensionless) 29,79-81,90-96,

100-107,112

r. Optical sensitivity

^constant

(N/m.lines)

²⁹

fi Fringe sensitivity (miIines)

²⁹

B Additional non-strain-related motion

(lines)

²⁹

la

Photoelastic constant for material

(N'rn.lines)

²⁹

T

Temperature (OC)

²⁹

w Wetness fraction

(dimensionless) 29,40

p Material

density (kg1m3) 29,30,37

k Thermal

conductivity (W/mOC) 29,30,37

D Moisture

diffusivity (m2/s) 29,30,39

C\O{ Saturated concentration

(kg/rn3) 29,30,39

C_p

Specific

^heat

(J/kgoC) 29,30,37

p_r

Vapor

pressure ^{in the} delamination

during 30,35,43-48

reflow

(Pa)

�(�)

Saturation water vapor pressure

30,38,43 corresponding

^{to reflow}

soldering

temperature (Pa)

RH_III Relative

humidity

^{at moisture}

conditioning 30,43 (dimensionless)

lV"Jr

Wetness in the delamination

during

^reflow

30,40,43 (dimensionless)

TAN CHEWPHENG McchEng.^{USM 06' -} XXi ^-

Listofsymbols

K

Multiplier depending

^{Poisson's ratio v and}

geometry (dimension less)

K⁼

(3

^-

4u)

^for

plane strain;

^K=

(3-u)/(l+v)

for

plane

^stress

f

Length

^{of die}

pad (m)

e

Length

^of

chip (m)

ar Thermal

diffusivity (m2/s)

h Convective heat transfer coefficient

(W/m20C)

Wo Initial wetness fraction

(dimensionless)

ao Initial delamination

length (m)

ae Allowed

length (m)

K/c

Plane strain fracture

toughness (MPa

^m

1/2)

(Jrs Tensile

strength (MPa)

(Jy Yield

strength (MPa)

5' Total extension

(m)

5e

Critical crack

edge (m)

c Linear strain

(dimensionless)

M External moment

(Nm)

/ Moment inertia

(rn")

6:;.-

^{Deflection at load F}

(m)

q Distributed load

(N/m)

F;

^{Virtual load}

(N) MI

^{Virtual moment}

(Nm) 58

^{Deflection of beam}

(m)

5{)

^Crack

edge en.largement by plate

deformation

(m)

TAN CHEWPHENGMechEng,^{USM 06' -} xxii ^-

31,32,45,46

33.35,36 33,45-48,114

37

37

40

49

49

49,51-55,62,66,114

51,59-69,110

52-56,62,71-73, 78,105-112

55

56,106-113

56,57

56-59,94-98 57,58,94-102

57,58 57,58 57,58,94

58

58

LISIofsymbols

A Area atthe center of thin

plate (m2)

⁵⁹

K/c

^Mean

plane

strain fracture

toughness (MPa

⁶⁰

m

1/2)

ar Mean

yield strength (MPa)

⁶⁰

<:

^Maximum

plane

^{strain fracture}

toughness 62,64,69 (MPa

^m

1/2)

K_IC,,"n Minimum

plane

^{strain fracture}

toughness 62,64,69 (MPa

^m

1/2)

p Pressure

loading (MPa)

^63,65,67

r;

^Tensile

loading,

^{70% less than critical 70-74}

loading (N)

Laser

wavelength (nm) 79-81,90-93.99.103

Illumination vector

(dimensionless) 79-82,90-94

o Observation vector

(dimensionless)

79-82,90-94

d

Displacement

^vector

(m) 79-81,90-94,99-112

¢>

^Deflection

angle (0) 80,90,94

r

Angle

between vectord and ^{x- z}

plane (0)

⁸⁰

PLD Path

length

^difference

(m)

⁸⁴

Lb

()y ^Path

length

^of

object

^beam

(m)

⁸⁴

LIe! Path

length

^{of reference beam}

(m)

⁸⁴

BR Beam

intensity

^ratio

(dimensionless)

⁸⁶

I'd

Reference beam

intensity (Lux)

⁸⁶

Ir/hj Object

^beam

intensity (Lux)

⁸⁶

eo

Observation

angle (0) 91,92

o,

Illumination

angle (0) 91,92,100

e

Rays angle (0) 92,93,103

TANruewPHENGMcchEng.^{USM06' - XXlH -}

Listofsymbols

fJ

^Rotation

angle (0) 93,103

!3,mg Image turning angle (0)

^97,98

x' Cantilever's coordinate

along

^{x' axes}

(m) 97,98

X

Image pixel along

^{X axes}

(pixel) 97,98

y

Image pixel along

^{y axes}

(pixel)

^97,98

r

Scaling

^factor

along

^{X axes}

(m/pixel)

⁹⁸

� Correcting

^{scale for}

holographic analysis 105,107,112 (dimensionless)

8u

^{Initial crack}

edge (m)

¹⁰⁸

TANCHEW^{PHENG Mcch}Eng.^{USM06' -} XXIV ^-

l.istofequations

Equation

^2.1

Equation

^2.2

Equation

^2.3

Equation

^2.4

Equation

^2.5

Equation

^2.6

Equation

^2.7

Equation

^2.8

Equation

^2.9

Equation

^2.10

Equation

^2.11

LIST OF EQUATIONS

Gtda=OFF'

=OFE+EFF'E'-OF'E'

G-JUI

^{taa F}

V=-F.o1 2

c=!_

F

G=

[2

(aci

2t Da

)

Ke =�GcE'

=

F;

(8C)EI

2t aa

K⁼

3FS1/-:;- [1.93 (.::)V2

^-

3.07(!:)l!Z

⁺

14.53(.::)51

^-

zs.u:

^.1

�':

^{+25.8 "}

-;

l

21 W ^{.. It' JIl JI" II. ii} J

=_6�_[1.93(�)V2

_tW,,2 ^IV

-3.o7'l.::)Ji: +14.53(")��

^{JI' \11 -25.11,II",:�:+25.S".H}

":l

�

F

[ ()V2 (

^\)12

( .5� ^.

'= ":

�

=- 11.58.E..

-18.42.E..)

^+87,181�, -150.66" +JS·U·J

tWV2 ^{IV w ,,,"': II H_}

K ^-

_fL_

•

f(!!_)

c

-

tWl/2

^W

( ) [

^{1'2 J"�}

,^' "

, "^-

�

f ^{E_ =}

11.58(�).' -IU2(!:)

-

+87.18:( -d

-

-150.66 ^,I

•

+15H ^,1

-

i

W ^{W II' \WJ ,II JI} J

Ke

⁼

t�J' ./(;)

f( �1_)=[177.6(!:.))lI2 _1113(!:.}l'� +3934.2'::"';'=

^{-6102 .1 ': ....)S33,� ,0:-}

JV ^{JI' IV \11 II} "_

TANCHEWPHENG McchEng.^{USM 06' -} XXV-

Page

11

11

11

12

12

12

12

12

13

13

14

LISI ofequations

Equation

^2.12

Equation

^2.13

Equation

^3.1

Equation

^3.2

Equation

^3.3

Equation

^3.4

Equation

^3.5a

Equation

^3.5b

Equation

^3.6

Equation

^3.7

Equation

^3.8

Equation

^3.9

Equation

^3.10

Equation

^3.11

G

=_1

(g(FcLJ2J

^__l

(_!3_(FeLJ2J

e 2£^I_I f³ W 2£^{' " 3} W

I 2 l)

15

Ke

⁼

JGcE· cosh(nn)

¹⁵

G=dlf_dc!>

da da

25

G ⁼ lim

_1_

r

⁽⁷

(

^{Sa- r,}

O)

^v

(r,

^Jr

)

^dr

&l-O2Lla

+lim

_1_

r

^r

(

^{Doa- r,}

O)

^u

(r,

^K

)

^dr

60-02�a

25

K2

K ² G=G_I +G₁₁ ^=�I• +_11•

E E

26

26

GI =lim�l-Fy

^- _2D.a1 ^{.s, 26}

26

(

^{. au}

J

J ⁼

Sr Udy

^{- T}_ax^ds

27

p^{,. =} PK"

(T ).

^{RHm • Wd.T}r

30

31

31

32

K)

⁼

JGIE· cosh(nn)

³²

TANCHEWPHENG McchEng.^{USM06' -} XXVI ^-

List ofequations

Equation

^4.1a

Equation

^{4.1 b}

Equation

^4.2a

Equation

^4.2b

Equation

^4.3

Equation

^4.4

Equation

^4.5

Equation

^4.6

Equation

^4.7

Equation

^4.8

Equation

^4.9

Equation

^4.10

Equation

^4.11

Equation

^4.12

Equation

^4.13

54

54

F

CJ=::---

(W-a)t

56

8'

E=-

L

56

(J⁼E'E 56

U=_l_

2EI

fM2dx

56

g

=8U

:F 8F

=_1

^El

fM(8M'Lv

^8F

r

57

F q=­w

57

57

BMx_:r

--=X

8F;

57

l

( qx' J

8_F

^• _i ^{=- F .x+M. +-}

(x')dx

El

I I

2

58

�

8 ^{== qa} :Fj 8EI

58

8 ^;::;

Fa4

:fj 8WE]

58

8^{B =}

2(0

^:Fj

)

⁼ 4WEI

Fa4

58

58

TANCHEW PHENGMechEns.^{USM06' - XXVll}

-

Listofequations

Equation

^4.14

p2a3

⁵⁸

G_e^{-- c} 2tWEI

Equation

^4.15

1 ⁼

t(L/2)3

⁵⁹

12

Equation

^{4.16 Fe =}

Aars

⁵⁹

=(W-a)tars

Equation

^4.17

a3 (W _a)2

^{f 2 59}

Ge

⁼ (J'rs

2WEI

Equation

^4.18

Ke =JGeE'

⁵⁹

=W'[(; r -(; rl(;� r

^u�

Equation

^5.1

( o-i)

^{. d=N•A 80}

Equation

^5.2

[::=}=[:�}A

81

o) ^-I

N) Equation

^5.3a

0=0 i+o j+o.k=

(Xc)i+(Yc)j+(z,)k

⁸¹

x y ^•

J(

^XC

/ +(Yc )2 +(

^Z,

)�

Equation

^{S.3b •}

_

'. '. .

_

(

^-Xa

)i+(

^-Ya

)j+{ -Za)k

⁸¹

l-lxl+1yJ+lzk-

_{2 2} .,

�(Xa) +(Yo) +(zoY

Equation

^{5.3c d=}

d)+dyj+d;k

⁸¹

Equation

^5.4

[

^Ox,

-ix 0)'1 -iy

^O"

-

i,

f' J [N, J

81 0x2 ^-

�x 0y2

-

ly

^0,,

= i, d,

=

�' (A J

0x3 ^- Ix

0y]

-

iy

^{o., l:}

d:

³

Equation

^5.5

(

^Ox,

-

�x

^0,,

= i: J(d}( N, }AJ

⁸¹

0x2 ^- Ix 0:2 lz

d, Nz

Equation

^5.6a .

(xc)i+(Zc)k

⁸²

0=0xl+O.k^{- =}

J(

^XC

)2 +( Zc)2

TANCIIEWPHENGMechEng.^{USM 06' -} XXVlll ^-

List ofequations

Equation

^5.6b

Equation

^5.7

Equation

^5.8

Equation

^5.9

Equation

^5.10

Equation

^5.11

Equation

^5.12

Equation

^5.13

Equation

^5.14

Equation

^5.15

Equation

^5.16

Equation

^5.17

82

PLD ⁼

Lob}

^-

Lrej

=0

84

86

d;:

^_

Lsin¢

d( L(l-cos¢)

90

(O; -iJ(d;:)=(N){A)

o -i ^:;::

(zc)

^_

(-za)

z z

J(Xc)2 +(zc)2 J(Xa)2 +(za)�

=cos

80

^-

(

^{- cos}

� )

91

91

91

d ⁼ NA

z

1+ cos

�

91

92

(sinO. +sinB,

^cose;

+COSll.)(�:J =(N)(A)

⁹²

92

d_z ^{= NA} 2^cos8

92

Equation

^{5.18a d. =}

dx

^cos

f3

⁺

d;

^sin

fJ

⁹³

Equation

^5.18b

d..

⁼

-dx

^sin

f3

⁺

dz

^cos

f3

⁹³

Equation

^5.19

d;

^{=0 93}

Equation

^{5.20 d, =}

-dz tanfJ

⁹³

TAN CHEW PHENGMcchEng.^{USM06' -} XXIX ^-

LISI ofequations

Equation

^{5.21 d. 93}

d,. ^;:::_-_

cos

f3

Equation

^{5,22 NA 93}

d.' ^;:::

2cos()cos

p

Equation

^{5.23 M}x-x ^=F.x+MI ⁹⁴

Equation

^5.24

8Mx_x

⁹⁴

--=x

of

Equation

^5.25

0,

^{F =}

;/ f (

^F•x+

M;) (

^x

)dx

⁹⁴

Equation

^5.26

F(L -0.015)3

⁹⁴

b:F

⁼

3£1

Equation

^5.27

Wt3

⁹⁵

1=- 12

Equation

^{5.28a x'cos}

Pimg

⁹⁸

r=

X

Equation

^5.28b

-f)

⁹⁸

Amg

^=tan _X

Equation

^5.29

d=,

^{=0 103}

Equation

^5.30

d;:::�

x ¹⁰³

tan

f3

Equation

^5.31

d,=�

r ¹⁰³

sin

f3

Equation

^5.32 _{d =} ^{NA 103}

x

'

2cos()sin

fJ Equation

^5.33

d,= N 104

x

0.7644^x

106 Equation

^5.34

C⁼ ae

(8 )

108 aL ^o

TANCHEWPHENGMechEng,^{USM 06' -} XXX-

\ 1"11,'�

PENGUKURAN KEKUATAN PATAH DALAM PAKEJ PBGA DENGAN MENGGUNAKAN KAEDAH UNSUR TERHINGGA DAN EKSPERIMEN

ABSTRAK

Pakej

^elektronik

khususnya jenis 'plastic

^ball

grid array' (PBGA) mempunyai kegagalan

^retakan dalaman yang unik yang berlaku ^disebabkan proses memateri.

Kewujudan kelembapan setempat

yang meresap ke dalam

pakej menghasilkan

^{tekanan wap. Semasa} proses ^memateri

Jenis

^aliran

(215°C), kelembapan

yang meresap akan mengewap ^{dan kemudian}

mengakibatkan

^retakan

'popcorn'.

^Oleh

itu,

^kaedah

berangka diperlukan

^untuk

memperihalkan rintangan patah

^{dalam bentuk} faktor keamatan

tegasan (SI F) geometri. Kemudian, kajian

ke atas kekuatan

patah

^bahan

epoksi

^sebatian

acuan

(EMC)

^{menentukan keadaan}

sempadan

untuk retakan

pakej,

Dalam

kajian ini, perisian Ansys

^telah

digunakan

^{untuk melakukan}

simulasi taburan

kelembapan

dan terma demi menentukan tekanan _wap

pada bahagian

^retak.

Daya

^tekanan wap ini ditindak ke atas PBGA untuk

memperolehi

^SIF

geometri dengan

penggunaan kaedah

penutupan

^retak terubahsuai

(MCCI). Didapati

bahawa kenaikan tekanan _{wap dan}

penambahan

saiz

lekangan menghasilkan

^SIF

geometri

^yang

tinggi. Perhubungan daya- pemanjangan

^{celah retakan} yang

diperolehi

^{menerusi kaedah}

holoqrafik

interferometri

(HI)

^dan

daya

^{kritikal D.E.R. 331}

sebagai

^{EMC telah}

digunakan

untuk menganggar ^kekuatan

patah.

^Kekuatan

patah

D.E.R 331 ialah 0.488MPa

Akhirnya,

^kekuatan

patah

^{D.E.R. 331 ini telah}

dibandingkan dengan

^SIF

geometri

^{untuk PBGA. Graf}

menunjukkan pelbagai

^keadaan

sempadan

1·\ '\('IIIW1'111.N(j Mcch1·:Il�.LJS,\.1 0(,' ^- XXXI ^-

selamat

pakej

^telah

diperolehi. Daripada graf ini,

^boleh

disimpulkan

^bahawa

PBGA masih selamat semasa proses

memateri,

iaitu tekanan _{wap 1.21}MPa dan nisbah

lekangan kurang daripada

^0.6.

Kegagalan pakej

^{elektronik ini}

dapat

dikawal

dengan

pengurangan ^{kesan tekanan} wap ^dan

lekangan

^antara

permukaan chip

^{dan EMC.}

- XXXII ^-

DETERMINATION OF FRACTURE TOUGHNESS IN PBGA PACKAGES USING FINITE ELEMENT AND EXPERIMENTAL METHODS

ABSTRACT

Electronic

packages especially

^the

plastic

^ball

grid

array

(PBGA)

^{has its}

unique

^{crack failure}

arising

^{from the}

soldering

process. The existence of moisture absorbed in

package

^{from ambient condition causes} vapor pressure.

During

^reflow

soldering

processes

(215°C),

the moisture absorbed

vaporizes

and

eventually

^causes popcorn

cracking. So,

^{numerical method is used to}

characterize the fracture resistance in terms of

geometric

^stress

intensity

^factor

(SIF). Then,

^the

investigation

^{of fracture}

toughness

^on epoxy

molding compound (EMC)

^material

provided boundary

conditions of

package cracking.

In this

research, Ansys

^{software was used to} simulate moisture diffusion and thermal transfer to determine the vapor pressure ^{at the crack}

region.

^The

vapor pressure

loading

^was

applied

^{on PBGA to obtain}

geometric

^SIF

using

modified crack closure

integral (MCCI)

^{method. It was} found that the increased in vapor pressure and

higher

delamination size created

high geometric

^SIF.

Load-crack

edge

extension relation obtained from

holographic interferometry (HI)

method and critical load for D.E.R. 331 as EMC material were used to evaluate fracture

toughness.

^{The fracture}

toughness

^{for D.E.R 331 was found}

to be 0.488MPa m

1/2.

Eventually,

^{the fracture}

toughness

^{for D.E.R. 331 was}

compared

^with

PBGA's

geometric

^{SIF. A}

graph

^with

package safety

^{conditions was obtained.}

From the

graph,

^{it can} be concluded that the PBGA is

typically

^{to be saved}

during soldering

process, where vapor pressure is 1.21^MPa and delarnmatron

I \, {III \\ PIli N{I Mcch I II!,:. llSM (lCl' ^- XXXlIl ^-

Abstract

ratio is less than 0.6. This EP's failure can be controlled

through minimizing

^the

effect

of

vapor pressure

and reducin_g die/EMC interface

delamination.

TAN ('I mw I'III�NQM.:�hEna.^{USM 06' -} XXXIV-

Chapter^I

CHAPTER 1

INTRODUCTION

1.1

Background

of research

Electronic

packaging (EP) designing

^and

manufacturing

^{tend to become}

a

challenging global industry.

^The

challenges emphasize

^on

making

^{the EP}

lighter, higher packaging density (miniaturization)

^{with the}

complexity

ⁱⁿ

functions ^and increased electrical

performance

^{while the cost remains at low}

level.

However,

^these

challenges

^of

packaging

^{are hard to} achieve and

bring

difficulties in

processing, handling

^and

understanding

^{of smaller}

components particularly

^{with the use of thinner dies. The matter}

arising

^{now is how to}

produce

^a

high reliability

^EP.

Higher density

^{and more}

compact developed systems

^are

turning

^the

manufacturers to surface mount

technology (SMT)

which needs full concern of failure mechanism inside

plastic package

^{which is known as} popcorn

cracking.

The

package

^is

highly

^{sensitive to moisture and}

humidity

conditions. Its

applications mostly

^{include consumer}

electronics,

^household

appliances, computing, automotive, telecommunications, flight control, robotics, military equipments

^and astronautics.

Plastic failure

usually happens

^{when the moisture diffused in the}

package during storage

^becomes

vaporized

^{and exerts a} pressure ^{known as} vapor pressure that could result in the popcorn effect.

Wong,

^{E.H. et al.}

(1998)

found that vapor pressure is

responsible

^{for the eventual} popcorn

cracking

^of

plastic integrated

^circuit

(Ie) packages during soldering

process.

Tay,

A.A.D. et al.

(1994)

^{mentioned that}

during soldering by

vapor

phase

reflow

(VPR)

^{or infrared}

(IR)

^reflow

(Figure 1.1)

^{or wave}

soldering techniques.

TANCHEW PHENG MechEng.^{USM 06' -} l ^-

Chapter ^I

the EP is heated up ^to solder

melting temperature

^{in the}

region

^of

215°C

^and

exposed

^to humid environment.

High

^{thermal stresses were} induced within the EP as the result of enhanced thermal mismatch between dissimilar materials.

Meanwhile,

^the

evaporation

of moisture caused

high

^stress

typically

^between

molding compound (MC)

^and

chip

interfaces. These stresses

mainly

contributed to the

phenomenon

^of

cracking

inside the EP

especially

^the

plastic

ball

grid

^array

(PBGA) during

^{the reflow}

soldering

process.

250--�---/---�-,---�

o T:

nl.l\.=24S0C±SOC

�

� 200 Tr=183°C 's^=70s

Q)

- - - - - - - - - - - - - - - - - -

'-

:J Rampup

ro^"- ISO Ramp ^down

2-30C/S/

el)

c.. 2�3°C/s

E

2^{O)c:: 100}

�, /

'i::^el)

/

Dry-out ^Reflow

-o ⁱ Pre-heat

C^<n 50

�

) Ambient^condition Cooling

o 2SoC

� Cl)

O

a::::

O 60 120 180 240 300

�oldering ^time, ts (s)

Figure

^{1.1: IR reflow}

soldering profile (OSRAM catalog, 2006, p.97)

From these

circumstances,

^{it is}

important

^to

study

the micro mechanics of interface delam ination and popcorn

cracking.

^Pa

rk,

^{Y. B. et al.}

(1997)

^noted

that the popcorn

cracking phenomenon

^{inside the} surface mounted

packages

was known

by assuming

^{an inherent}

edge

^{crack at die}

pad/epoxy molding compound (EMC)

^{interface and}

subsequently

interface delamination under thermal arid vapor pressure

loadings. According

^to<