Nouvelles Brasures Sans Plomb Conception Des Dispositifs D'essai, Fabrication Des Échantillons et Caractérisation.doc

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THESE DE DOCTORAT
DE L'UNIVERSITE PARIS-SACLAY
Préparée a
L’Université de Versailles Saint-Quentin-en-Yvelines
0
ÉCOLE DOCTORALE N 580 (STIC)
Par
M. Quang Bang TAO
Titre de la thèse:
Nouvelles Brasures Sans Plomb: Conception Des Dispositifs D'essai,
Fabrication Des Échantillons et Caractérisation
Titre de la thèse en anglais:
New Lead-Free Solders: Testing Device Development, Specimen
Fabrication, and Characterization
Thèse présentée et soutenue à Vélizy, le 06 Décembre 2016 :
Composition du Jury:
M. Fabrice Brémand Professeur, Université de Poitiers, Institut Pprime Rapporteur
M. Abdelkhalak El Hami Professeur, INSA de Rouen Rapporteur
M. Yves Bienvenu Professeur honoraire, ParisTech Examinateur
M. Frédéric Mazaleyrat Professeur, ENS Cachan, Université Paris Saclay Président
Mme. Florence Le-Strat Expert, Renault Technocentre Examinateur
M. Yasser Alayli Professeur, UVSQ, Université Paris Saclay Invité
M. Jean-Michel Morelle Expert, Valeo, France Invité
M. Lahouari Benabou MCF-HDR, UVSQ, Université Paris Saclay Co-Directeur
M. Fethi Ben Ouezdou Professeur, UVSQ, Université Paris Saclay Directeur

ÉCOLE DOCTORALE
Sciences et technologies
de l'information
et de la communication (STIC)
Titre: Nouvelles Brasures Sans Plomb: Conception Des Dispositifs D'essai, Fabrication Des Échantillons et
Caractérisation
Mots clés: Sans-Plomb Brasures, Microstructure, Etude mécanique,
Fiabilité Résumé:
De nos jours, une des stratégies pour améliorer les
propriétés des brasures sans plomb est d'introduire en
petites quantités certains éléments d'alliage. Dans notre
étude, deux nouveaux types de brasures, dénommés
Innolot et SAC-Bi et dont l'utilisation dans diverses
applications électroniques augmente, sont caractérisées.
En particulier, l'effet des éléments Ni, Sb et Bi sur les
propriétés mécaniques est analysé. L'étude vise
également à évaluer l'influence des facteurs de
sollicitation, du vieillissement en température sur la
réponse des matériaux et leurs évolutions
microstructurales. A cet effet, une machine permettant
de réaliser des essais de micro-traction sur éprouvettes
miniatures a été conçue et fabriquée. Les sollicitations
qu'elle permet d'appliquer sont multiples (traction,
cisaillement et cyclage) et des conditions en température
et en vitesse de déformation peuvent être imposées lors
de l'essai. La fabrication des éprouvettes nécessaires
aux essais a également été entreprise dans cette étude
afin d'avoir un matériau similaire à celui issu du process
industriel et de disposer d'une géométrie adaptée au
type de caractérisation souhaitée (éprouvettes massives,
à simple recouvrement, etc.).
Après ces étapes préparatoires, des tests ont été réalisés
sous sollicitations de traction, cisaillement, fluage
et fatigue en faisant varier les conditions d'essais. Le
premier objectif a été l'identification du comportement
des brasures, y compris en prenant en compte l'effet du
vieillissement. Ces données ont permis ensuite de
réaliser des simulations thermo-mécaniques sur les
matériaux utilisés sous forme de joints de brasure dans
un module de puissance sous cyclage thermique. Les
analyses de microstructure (SEM/EDS et EPMA) faites
par la suite ont montré le rôle des éléments d'alliage (Ni,
Sb et Bi) sur les performances mécaniques des brasures
en termes de résistance, limite élastique et rigidité. Le
rôle des facteurs d'essai, comme la température, la
vitesse de sollicitation et la durée de vieillissement, a
également été mis en évidence au niveau des propriétés
obtenues et des changements dans la microstructure. Il a
été établi que l'élément Sb permet de favoriser le
durcissement par écrouissage des brasures, tandis que
l'ajout des éléments Ni et Bi permettent un raffinement de
la microstructure. Les essais ont aussi permis d'identifier
les 9 paramètres de la loi d'Anand par une procédure
numérique s'appuyant sur les données de traction et de
cisaillement, permettant ainsi de réaliser des simulations
par éléments finis. Ces dernières suggèrent un meilleur
comportement à la fatigue pour la brasure Innolot qui
bénéficie est effets favorables des additifs.
Title: New Lead-Free Solders: Testing Device Development, Specimen Fabrication, and Characterization
Key words: lead-free solder, minor alloying additions, microstructure, reliability, mechanical study.
Abstract:
Nowadays, one of the strategies to improve the reliability
of lead-free solder joints is to add minor alloying
elements to solders. In this study, new lead-free solders,
namely InnoLot and SAC387-Bi, which have begun to
come into use in the electronic packaging, were
considered to study the effect of Ni, Sb and Bi, as well as
that of the testing conditions and isothermal aging, on
the mechanical properties and microstructure evolution.
A new micro-tensile machine are designed and
fabricated, which can do tensile, compressive and cyclic
tests with variation of speeds and temperatures, for
testing miniature joint and bulk specimens. Additionally,
the procedure to fabricate appropriate lap-shear joint and
bulk specimens are described in this research. The tests,
including shear, tensile, creep and fatigue tests, were
conducted by micro-tensile and Instron machine at
different test conditions. The first study is to characterize,
experimentally, the mechanical behaviors and life time of
solder joints submitted to isothermal aging and
mechanical tests. The second goal of the project is to
perform thermo-mechanical simulations of IGBT under
thermal cycling. The experimental results indicate that, with
addition of Ni, Sb and Bi in to SAC solder, the stress levels
(UTS, yield stress) are improved. Moreover, testing
conditions, such as temperature, strain rate, amplitude,
aging time, may have substantial effects on the mechanical
behavior and the microstructure features of the solder alloys.
The enhanced strength and life time of the solders is
attribute to the solid hardening effects of Sb in the Sn matrix
and the refinement of the microstructure with the addition of
Ni and Bi. The nine Anand material parameters are identified
by using the data from shear and tensile tests. And then, the
obtained values were utilized to analyze the stress-strain
response of an IGBT under thermal cycling. The results of
simulations represent that the response to thermal cycling of
the new solders is better than the reference solder,
suggesting that additions of minor elements can enhance
the fatigue life of the solder joints. Finally, the SEM/EDS and
EPMA analysis of as-cast, as-reflowed as well as fractured
specimens were done to observe the effects of these above
factors on the microstructure of the solder alloys.
i

Abstract
Due to the RoHS and WEEE legislations for restricting the use of six hazardous materials
in the manufacture of various types of electronic and electrical equipment, developing novel Pb-
free solders becomes a real challenge for many industrials in recent years. Mechanical
properties of the lead-free alloys are very important factors in the design and reliability
evaluation of the soldered joints. One of the strategies to improve the reliability of lead-free
solder joints is to add minor alloying elements to solders. Indeed, many researchers have
demonstrated that the properties of Sn-Ag-Cu (SAC) solders can be enhanced with small
additions of elements such as Bi, Ni, Sb, Zn, Ce,...Among the newly-developed lead-free solder
alloys, SAC387-Bi and SAC-Bi,Ni,Sb (InnoLot) alloys, which contain minor quantities of Sb, Bi
and Ni, have been identified as promising candidates for the automotive industry. In operation,
the microstructure, mechanical response, and failure behaviour of the lead-free solder joints in
the electronic assemblies are highly dependent on external factors such as the imposed
thermal loads, the mechanical vibrations, the effect of aging, etc. Hence, it is essential to
understand how the mechanical properties of the newly-developed solder alloys vary with
changes in testing conditions (strain rate, temperature), composition, and isothermal aging.
The first study is to characterize, experimentally, the mechanical behaviors and life time of
solder joints using these new lead-free solders submitted to isothermal aging and accelerated
thermo-mechanical tests. Firstly, a ‘home-made’ micro-tension machine, which can do tensile,
compressive and cyclic tests with variation of speeds and temperatures, is designed and
fabricated for testing miniature solder joint specimens. Furthermore, a uniaxial Instron machine
is used for testing flat and cylindrical bulk specimens. The detailed procedures for fabricating all
these types of specimens will be described in the manuscript. Shear and creep tests on lap-
shear solder joint specimens were performed with the micro-tension machine. Uniaxial tensile
and cyclic fatigue tests for flat and cylindrical bulk specimens were carried out on Instron
universal machine under various testing conditions. In addition, in order to investigate the effect
of aging several joint and bulk samples were kept in thermal oven at 1000
C for different
aging times (0-12 months) and then used for creep and tensile tests. The experimental
results indicate that, with addition of Ni, Sb and Bi into referenced SAC solder, the
stress levels (UTS, yield stress) are improved. Moreover, testing conditions, such as
temperature, strain rate, amplitude, aging time, may have substantial
ii

effects on the mechanical behavior and the microstructure features of the solder alloys. The
enhanced strength and life time of the solders are attributed to the solid hardening effects of Sb
in the Sn matrix and the refinement of the microstructure with the addition of Ni and Bi.
The second goal of the project is to perform thermo-mechanical simulations of IGBT under
thermal cycling. Based on the experimental results, the procedure for extracting the nine Anand
material parameters was introduced using the data from shear and tensile experiments. The findings
with regard to the Anand viscoplastic constitutive model predictions are in good agreement with the
experimental data and previous studies for other solder alloys. And then, the obtained values were
utilized to analyze the stress-strain response of an IGBT under thermal cycling. The developed
Anand constitutive equations have been implemented within the finite element code ABAQUS. The
results of simulations show that the response to thermal cycling of the new solders are better than
the reference solder, suggesting that additions of minor elements can enhance the fatigue life of the
solder joints. The creep activation energy and stress exponent values were also obtained from creep
data by using the Dorn power model.
Finally, the SEM/EDS and EPMA analysis of as-cast, as-reflowed as well as
fractured specimens were done to observe the effects of testing conditions, alloying
elements, and aging on the microstructure of the solder alloys.
iii

Acknowledgements
I am indebted to many people for the help along the journey.
Most importantly, I would like to express my sincere gratitude to my supervisor,
Professor Lahouari Benabou for introducing me to very exciting research areas, for the
continuous guidance, supervision and untiring support for my PhD study, and related
research. I want to say again a special thank you to Professor Benabou, for his
collaborative approach to research and good nature. This gave me great opportunities to
gain a lot of research experiences, knowledge, and working methodology. When I had
problems in my research, he was willing to give me many useful advice and suggestions. I
could not have imagined having a better advisor and mentor for my PhD research.
In addition, I would like to thank Professor Fethi Ben Ouezdou for his direction and
his availability despite his many administrative responsibilitiesin the University of
Versailles over the last years, as well as Professor & Director of LISV Luc Chassagne
for welcoming and allowing me to do my research in his laboratory.
I would also like to express my gratitude to many Professors in the University Paris-Saclay
for their lectures. My sincere thanks are to all members of the review committee for taking time
to examine my work and for providing valuable advices during my dissertation evaluation.
I would like to thank the industrial partners and experts from Valeo, special thanks to J.M.
Morelle, M. Vivet, and K.L. Tan. They have played a critical role in this work through helpful
discussions, guidance, and advice. Concerning my comrades in the laboratory LISV, whether
they are PhD students or technicians, their friendship, and moral support made my life
much easier in France.
I must thank also the Vietnamese Government for providing me with the financial support to
carry out this work during three years and to obtain the PhD degree. Similarly, I must thank the
company Valeo for helping me with a financial complement to my scholarship.
Last but not the least, I am grateful to my parents, my family, my parents in-law and
my siblings for their support and understanding. Special thanks to my wife Ngoc Anh
and lovely daughter Minh Chau, for their endurance, perseverance, heartfelt
consideration. Their smile kept my spirit high during all these years.
TAO Quang Bang
iv

Table of Contents
Abstract.....................................................................................................................................................i
Acknowledgements.............................................................................................................................iv
List of Figures .......................................................................................................................................ix
List of Tables...................................................................................................................................... xiii
List of Abbreviations .........................................................................................................................xiv
List of Publications .............................................................................................................................xv
CHAPTER 1:.......................................................................................................................................... 1
GENERAL INTRODUCTION ............................................................................................................ 1
1.1. Introduction..................................................................................................................................... 2
1.2. Lead-free Solders......................................................................................................................... 3
1.3. Sn-Ag-Cu Solder Alloys as Popular Choices ...................................................................... 4
1.4. Novel Lead-free Solder Alloys for Automotive Industry ................................................... 7
1.5. Mechanical Properties of Solder Materials .......................................................................... 8
1.5.1. Tensile Stress and Strain ............................................................................................... 9
1.5.2. Creep ..................................................................................................................................11
1.5.3. Shear...................................................................................................................................13
1.5.4. Fatigue................................................................................................................................15
1.6. Research Objectives.................................................................................................................17
1.7. Organization of the Dissertation............................................................................................18
CHAPTER 2:........................................................................................................................................21
LITERATURE REVIEW ....................................................................................................................21
2.1. Introduction...................................................................................................................................22
2.2. Effect on Mechanical Properties and Microstructure of Alloying Elements Added to the
Sn-Ag-Cu System...............................................................................................................................23
2.3. Effects of Strain Rate and Temperature on Solder Joints.............................................24
2.4. Effect of Aging Time on Solder Material Properties ........................................................24
2.5. Constitutive Modeling for Solder Materials.........................................................................26
2.5.1. Constitutive Modeling for Stress-Strain Tests........................................................27
2.5.2. Constitutive Modeling for Creep Tests.....................................................................28
2.6. Digital Image Correlation .........................................................................................................29
v

2.7. Summary and Discussion........................................................................................................29
CHAPTER 3:........................................................................................................................................33
MICRO-TENSION MACHINE AND THE INTERFACE...........................................................33
3.1. Introduction...................................................................................................................................34
3.2. Design of the Micro-tension Machine ..................................................................................34
3.3. The Control Interface ................................................................................................................40
3.3.1. LabView Interface for Tensile and Shear Tests ....................................................40
3.3.2. LabView Interface for Creep Test..............................................................................41
3.3.3. Data Acquisition...............................................................................................................42
CHAPTER4: .........................................................................................................................................45
SPECIMEN PREPARATION AND EXPERIMENTAL TESTING.........................................45
4.1. Introduction...................................................................................................................................46
4.2. Lead-Free Solder Materials ....................................................................................................47
4.3. Solder Joint Specimen Preparation Procedure ................................................................48
4.4. Solder Bulk Specimens Preparation Procedure...............................................................54
4.4.1. Solder Bulk Specimens for Tensile Tests................................................................54
4.4.2. Solder Bulk Specimens for Fatigue Tests...............................................................56
4.5. Experimental Plan......................................................................................................................57
4.5.1. Shear and Creep Tests.................................................................................................57
4.5.2. Tensile and Fatigue Tests............................................................................................60
4.5.3. Aging Specimens for Creep and Tensile Tests.....................................................65
4.6. Microstructure Analysis ............................................................................................................66
CHAPTER 5:........................................................................................................................................69
EXPERIMENTAL RESULTS...........................................................................................................69
5.1. Introduction...................................................................................................................................71
5.2. Microstructure Analysis ............................................................................................................71
5.2.1. Microstructure and Distribution of Elements for As-cast Specimens..............72
5.2.2. As-fabricated Microstructure Analysis of Solder Joint Specimens ..................75
5.3. Results of Shear Tests.............................................................................................................77
vi

5.3.1. Shear Strain-Stress Curves.........................................................................................77
5.3.2. Effects of Testing Conditions and Alloying Elements on Mechanical Properties 79
5.3.3. Fractured Solder Joints After Shear Tests..............................................................82
5.4. Tensile Behavior.........................................................................................................................85
5.4.1. Tensile Stress-Strain Curves.......................................................................................85
5.4.2. Effects of Testing Conditions and Alloying Elements on UTS and Yield Stress 86
5.4.3. Effects of Testing Conditions and Alloying Elements on Young’s modulus and
Elongation......................................................................................................................................89
5.4.4. Microstructure Analysis of Fractured Solder Bulk Specimens after Tensile Tests 90
5.5. Creep Behavior...........................................................................................................................94
5.5.1. Creep Curves ...................................................................................................................94
5.5.2. Effects of Applied Stress and Temperature on Creep Behavior ......................95
5.5.3. Fractured Solder Joints after Creep Tests..............................................................97
5.6. Fatigue Behavior ......................................................................................................................100
5.6.1. Overview of Cyclic Stress-Strain Behavior ...........................................................100
5.6.2. Fatigue Test Results....................................................................................................101
5.6.2.1. Cyclic Stress Response Behavior ..................................................................104
5.6.2.2. Effect of Temperature on Fatigue Life...........................................................107
5.6.2.3. Effect of Frequency (Strain Rate) on Fatigue Life.....................................106
5.7. Effect of Isothermal Aging .....................................................................................................107
5.7.1. Aging Effect on Tensile Properties..........................................................................107
5.7.1.1. Effect of 1 day Aging at 1000
C........................................................................107
5.7.1.2. Effect of 5 days, 30 days and 90 days Aging at 1000
C...........................108
5.7.2. Aging Effect on Creep Behavior...............................................................................110
5.7.2.1. Creep Behavior after Aging ..............................................................................110
5.7.2.2. Effect of Aging Time on the Microstructure in the case of creep..........111
5.8. Summary and Conclusion .....................................................................................................114
CHAPTER 6:......................................................................................................................................117
CONSTITUTIVE MODELS ANDFINITE ELEMENT SIMULATION..................................117
6.1. Introduction.................................................................................................................................118
6.2. Anand Viscoplastic Constitutive Model .............................................................................118
6.2.1. Determination of the Anand Material Parameters for Shear Strain-Shear Stress and
Tensile Strain-Stress Data .....................................................................................................123
vii

6.2.2. Correlation of the Anand Model Predictions and Experimental Results......124
6.3. Creep Constitutive Model ......................................................................................................128
6.4. Finite Element Simulation of the Solder Joint in the IGBT Module Under Thermal Loading
132
6.4.1. Insulated-Gate Bipolar Transistor Configuration.................................................132
6.4.2. The Finite Element Model ..........................................................................................133
6.4.3. Loading Conditions.......................................................................................................134
6.4.4. FE Results and Discussion........................................................................................135
6.5. Summary and Conclusion .....................................................................................................138
CHAPTER 7:......................................................................................................................................140
SUMMARY, CONCLUSIONS AND PERSPECTIVES..........................................................140
7.1. Literature Review .....................................................................................................................141
7.2. Testing Device Development, Specimen Preparation and Experimental Setup..142
7.3. Effects of Element Additions, Testing Conditions and Aging on Mechanical Properties and
Microstructure of Solder Alloys.....................................................................................................142
7.4. The Anand Viscoplastic Constitutive Model and Power Creep Model ....................144
7.5. Thermal Cycling Reliability Prediction for Lead-Free Solder Joint in IGBT Assemblies
...
144
7.6. Perspectives ..............................................................................................................................145
Bibliography........................................................................................................................................147
viii

List of Figures
Figure 1.1. Lead-free Solder Market Share.
Figure 1.2. Prevailing Lead-free Solder Choices and Their Applications.
Figure 1.3. SAC Ternary Phase Diagram.
Figure 1.4. SEM Micrograph of Typical SAC Solder.
Figure 1.5. Testing Schematic for Solder Alloys.
Figure 1.6. Typical Stress-Strain Response for Ductile Materials.
Figure 1.7. Typical Creep Response for Ductile Materials.
Figure 1.8. Typical Shear Stress-Strain Response for Ductile Materials.
Figure1.9. A hysteresis loop for fatigue test of total strain range of 0.3% at room
temperature and 0.0033 Hz.
Figure 1.10. A relationship between tensile stress amplitude with number of cycles for
total strain range of 0.3% at room temperature and 0.0033 Hz. Figure 3.1. The overall
experimental setup.
Figure 3.2. Schematic of the gripping: (a), (b) dimension of gripping (unit: mm) and (c),
(d) the established griping.
Figure 3.3. LVDT (a) and Load cell (b) sensors used for the micro-tester.
Figure 3.4. The signal conditioner for LVDT (a) and load cell (b).
Figure 3.5. Heating foil (a) and thermocouple (b).
Figure 3.6. The DAQ 16-bit National Instrument card.
Figure 3.7. The micro-tensile machine.
Figure 3.8.LabView interface used for monotonic tests.
Figure 3.9.LabView interface used for creep test.
Figure 3.10. Basic data acquisition.
Figure 3.11. Configuration of the DAQ assistant.
Figure 4.1. Schematic for types of specimens and experimental setup
Figure 4.2. Electrical Discharge Machining machine.
Figure 4.3. Solder flux gel.
Figure 4.4. Solder sheets.
Figure 4.5. The reflow profiles: SAC-Bi solder joint (a); InnoLot solder joint (b).
Figure 4.6. The fixture for the assembled specimen during the reflow process: the drawing (a)
and actual fixture (b) (unit: mm).
ix

Figure 4.7. The procedure for fabricating a lap shear joint specimen (a), its dimension (b).
Figure 4.8. Solder material (a), graphite cup (b), and metal mold (c).
Figure 4.9.The procedure for fabricating the flat dog-bone bulk specimens and their
dimensions (all dimensions are in mm).
Figure 4.10. Dimension of the cylindrical specimen and its actual specimen.
Figure 4.11. Shear and Creep Experimental Setup.
Figure 4.12. The testing apparatus for the tensile and fatigue tests.
Figure 4.13. Typical stress-strain curve for InnoLot solder alloy.
Figure 4.14.Stress-strain curves for different samples subjected to the same testing conditions.
Figure 5.1. SEM (a) and EPMA (b) machines.
Figure 5.2. The microstructures of the as-cast: SAC-Bi (a) and InnoLot (b).
Figure 5.3. The mapping of several elements in InnoLot solder detected by EPMA.
Figure 5. 4. The global view of the lap shear joints and the IMCs morphology: (a) SAC-
Bi (b) InnoLot.
Figure 5.5. Shear stress-strain curves at different strain rates under room temperature
for: (a) SAC-Bi solder joint and (b) InnoLot solder joint.
Figure 5.6. Shear stress-strain curves at different testing temperatures under the strain
rate of 2.0 x 10-4
s-1
Figure 5.7. Dependence of UTS on strain rate at different testing temperatures for: (a)
SAC-Bi solder joint and (b) InnoLot solder joint.
Figure 5.8. Dependence of yield stress on strain rate at different testing temperatures
Figure 5.9. Cross-sectional SEM images after a shear test at strain rate of 2.0 x 10-4
s-
1
and room temperature for SAC-Bi solder joint.
s-1
and room temperature for InnoLot solder joint.
s-1
and 1250
C for SAC-Bi solder joint.
s-1
and 1250
C for InnoLot solder joint.
Figure 5.13. The obtained uniaxial tensile curves for the InnoLot solder under all
conditions (strain rates, temperatures) considered in the study.
x

Figure 5.14. The effects of strain rate and temperature on the ultimate tensile strength
(a) and yield stress (b) of InnoLot solder alloy.
Figure 5.15. The influence of strain rate and temperature on the Young’s modulus (a)
and the elongation to rupture (b) of the InnoLot solder.
Figure 5.16. The details of fracture surfaces observed by EPMA after tensile testing
under different temperatures at the same strain rate of 2.0 x 10-4
s-1
.
Figure 5.17. The details of fracture surfaces observed by EPMA after tensile testing
under different strain rates at the same testing temperature of 250
C.
Figure 5.18. SEM micrographs of fracture surfaces under tensile testing at different strain
rates for testing temperature of 250
C: (a) 2.0 x 10-3
s-1
, (b) 2.0 x 10-4
s-1
,(c) 2.0 x 10-5
s-1
.
Figure 5.19. SEM micrographs of fracture surfaces under tensile testing at different
temperatures for strain rate of 2.0 x 10-3
s-1
: (a) 250
C, (b) 1250
C.
Figure 5.20. A typical creep curve of the InnoLot solder joint at 250
C and applied
stress of 25.25 MPa.
Figure 5.21. The typical set of creep curves of the InnoLot solder joints at
temperatures of 250
C for different applied stress levels.
Figure 5.22. The typical set of creep curves at various temperatures and the same
stress level of 11.875 MPa.
Figure 5.23. The SEM images of creep tests under 18.75 MPa at 250
C: (a) global
image, (b) details at different areas.
Figure 5.24.The SEM images of creep tests under 18.75 MPa at 1250
C: (a) global
image, (b) details at different areas.
Figure 5.25. The cyclic strain control for cyclic fatigue test.
Figure 5.26. Typical cyclic stress-strain testing for InnoLot solder.
Figure 5.27. The cyclic stress-strain hysteresis loop at the 10th cycle, for 0.4% total strain
0
range, temperature of 25 C and frequency of 0.0025 Hz.
Figure 5.29. Relationship between tensile stress amplitude with number of cycles for
total strain range of 0.3% at 250
C and 0.025 Hz.
Figure 5.30. The typical cyclic stress behavior of the InnoLot solder: (a) 250
C and (b)
1250
C and different total strain ranges.
Figure 5.31.Hysteresis loops for total strain range of 0.1% at 0.025 Hz at 250
C and 1250
C.
xi

Figure 5.32. Hysteresis loops for total strain range of 0.1% and 250
C at: (a) 0.1 Hz and
(b) 0.01 Hz.
0
Figure 5.33. Influence of aging on stress-strain curves of InnoLot after 1 day at 100 .
Figure 5.35. Influence of aging on creep curves of InnoLot.
Figure 5.36. The SEM images after the creep test with applied stress of 18.75MPa at
250
C and aging at 1000
C for 1 month.
250
C and aging at 1000
C for 2 month.
250
C and aging at 1000
C for 2 month.
Figure 6.1. Plots of the saturation stress versus steady-state strain rate from shear tests:
experimental results and Anand model predictions for (a) SAC-Bi, and (b) InnoLot.
Figure 6.2. Relations between inelastic strain and stress for (a) SAC-Bi, and (b)
InnoLot: comparison between experimental results and Anand model fits at three strain
rates for the temperature 250
C (extraction from shear tests).
Figure 6.3.Experimental and simulated stress-strain responses of InnoLot solder
(extraction from tensile tests).
Figure 6.4. Creep activation energy values of the InnoLot solder joints at different stress levels
Figure 6.5. Stress exponent of the InnoLot solder joints at different temperatures
Figure 6.6. Schematic of an IGBT power module.
Figure 6.7.Configuration of the IGBT module.
Figure 6.8. Finite element model for one-quarter of the IGBT module.
Figure 6.9. Thermal cycling profile considered in FE analysis.
Figure 6.10. Von Mises stress distribution in the bottom solder joint after 6 cycles in the
case of: (a) InnoLot and (b) SAC387.
Figure 6.11. Evolution of the accumulated equivalent inelastic strain in the two types of
solders during thermal cycling.
Figure 7.1.DIC technique for solder specimens.
xii

List of Tables
List of Tables
Table 4.1. Chemical compositions of the solder alloys (mass %), and the solidus and
liquidus temperatures.
Table 4.2. (a) The shear test matrix, (b) The creep test matrix.
Table 4.3. Uniaxial tensile test matrix.
Table 4.4. Cyclic Fatigue Testing Conditions.
Table 4.5. Aging Matrix for Tensile and Creep Tests.
Table 5.1.Cyclic fatigue matrix test.
Table 5.2.Material Properties for InnoLot, 1 day aging at 1000
C for two strain rates.
Table 5.3. Aging effects on material properties of InnoLot.
Table 6.1. Anand material parameters for several solder alloys.
Table 6.2. The discirption and unit of 9 Anand parameters.
Table 6.3. The Anand model parameters determined for SAC-Bi and InnoLot lead-free solders.
Table 6.4. Dimensions of the components in the IGBT module.
Table 6.5. The elastic properties of all materials used in the model.
xiii

List of Abbreviations
List of Abbreviations
EDM - Electrical Discharge Machining
SEM - Scanning Electron Microscope
EPMA - Electron Probe Micro-Analyze
EDS - Energy-Dispersive Detector
EDX - Energy-Dispersive X-ray spectroscopy
WEEE - Waste Electrical and Electronic Equipment
RoHS - Restriction of Hazardous Substances Directive
EU - European Union
Pb - Lead
Sn - Tin
Bi - Bismuth
Ni - Nikel
Sb - Antimony
SAC - Sn-Ag-Cu
PCB - Printed Circuit Board
DCB - Direct Copper Bon
UTS - Ultimate Tensile Stress
E - Young’s modulus
YS - Yield Stress
CTE - Coefficient of Thermal Expansion
IMC - Intermetallic Compound
DIC - Digital Image Correlation
IGBT - Insulated-Gate Bipolar Transistor
FEM - Finite Element Method
FEA - Finite Element Analysis
AFM - Atomic-Force Microscopy
LVDT - Linear Variable Differential Transformer
DAQ - Data Acquisition
ASTM - American Society for Testing and Materials
BGA - Ball Grid Array
xiv

List of Publications
List of Publications
1. Q.B. Tao, L. Benabou, L. Vivet, V.N. Le and F. Ben Ouezdou. “Effect of Ni and Sb
additions and testing conditions on the mechanical properties and microstructures of
lead-free solder joints”. Materials Science and Engineering: A, 669, 403-416; 2016.
2. Q.B. Tao, L. Benabou, K.L. Tan, J.M. Morelle, V.N. Le and F. Ben Ouezdou. “A
design of a new miniature device for solder joints’ mechanical properties
evaluation”. Proceedings of the Institution of Mechanical Engineers, Part C:
Journal of Mechanical Engineering Science; 0954406216654728; 2016.
3. Q.B. Tao, L. Benabou, V.N. Le, H. Hwang and D.B. Luu. “Viscoplastic characterization
and Post-rupture microanalysis of a novel lead-free solder with small additions of Bi,
Sb and Ni”. Journal of Alloys and Compounds, 694, 892-904; 2016.
4. Q.B. Tao, L. Benabou, K.L. Tan, J.M. Morelle and F. Ben Ouezdou. “Creep
behavior of Innolot solder alloy using small lap-shear specimens”. IEEE, 17th
Electronics Packaging Technology Conference (EPTC), Singapore, Dec.; 2015.
5. Q.B. Tao, L. Benabou, K.L. Tan, J.M. Morelle, L. Chassagne and F. Ben Ouezdou.
“Evaluation of the creep behavior of lead-free SnAgCuBiNi solder joints using in-
situ micro-tensile testing”. 13th International Conference on Creep and Fracture of
Engineering Materials and Structures, Toulouse, Apr.; 2015.
6. L. Benabou and Q.B. Tao. “Approche multi-échelle de la rupture d'un alliage
d'étain pour le brasage en électronique de puissance”. AFM, Association
Française de Mécanique; 2015.
7. V.N. Le, L. Benabou, V. Etgens and Q.B. Tao. “Micromechanical model for
describing intergranular fatigue cracking in a lead-free solder alloy”. Procedia
Structural Intergrity. 2, 2614-2622; 2016.
8. V.N. Le, L. Benabou, V. Etgens and Q.B. Tao. “Finite element analysis of the effect
of process-induced voids on the fatigue lifetime of a lead-free solder joint under
thermal cycling”. Microelectronics Reliability. In Press; 2016.
9. V.N. Le, L. Benabou, V. Etgens and Q.B. Tao. “Modeling of intergranular thermal
fatigue cracking of a lead-free”. International Journal of Solids and Structures. In-
Press, Accepted Manuscript; 12/2016.
10. L. Benabou and Q.B. Tao. “Development and first assessment of a DIC system for
micro-tensile tester used for solder characterization”. Experimental Techniques.
Under Revision; 11/2016.
xv

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