Electrical Conductive Adhesives with Nanotechnologies

444 Pages·2010·13.488 MB·English

by  Yi Li, Daniel Lu, C. P. Wong (auth.)

Electrical Conductive Adhesives
with Nanotechnologies
· ·
Yi Li Daniel Lu C.P. Wong
Electrical Conductive
Adhesives with
Nanotechnologies
123
YiLi DanielLu
SchoolofMaterialsScience HenkelLoctite(China)Co.Ltd.
andEngineering 5000W.ChandlerBlvd.
GeorgiaInstituteofTechnology 264006Chandler
771FerstDrive People’sRepublicofChina
Atlanta,GA30332-0245 [email protected]
USA
[email protected]
C.P.Wong
SchoolofMaterialsScience
andEngineering
GeorgiaInstituteofTechnology
771FerstDrive
Atlanta,GA30332-0245
USA
[email protected]
ISBN978-0-387-88782-1 e-ISBN978-0-387-88783-8
DOI10.1007/978-0-387-88783-8
SpringerNewYorkDordrechtHeidelbergLondon
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(cid:2)c SpringerScience+BusinessMedia,LLC2010
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Preface

With the phasing out of lead-bearing solders, electrically conductive
adhesives (ECAs) have been identified as one of the environmentally
friendly alternatives to tin/lead (Sn/Pb) solders in electronics packaging
applications. In particular, with the requirements for fine-pitch and high-
performance interconnects in advanced packaging, ECAs with nano-
materials or other nano-technology are becoming more and more important
due to the special electrical, mechanical, optical, magnetic, and chemical
properties that nano-sized materials can possess. There has been extensive
research for the last few years on materials and process improvement of
ECAs, as well as on the advances of nanoconductive adhesives that
contain nano-filler, such as nano-particles, nanowires, or carbon nanotubes
and nano monolayer graphenes.

The objective of this book is to review the most recent advances of various
types of electrically conductive adhesives with the particular emphasis on
the emerging nanotechnology, including materials development and
characterizations, processing optimization, reliability improvement, and
future challenges/opportunities identification.

This book consists of nine Chapters, each representing a specific field of
interest. Chapter 1 discusses an overview of electronic packaging and the
evolvement of different types of conductive adhesives. Chapter 2 describes
the latest development of nano-materials, nanotechnology and their
applications in microelectronics packaging. Chapter 3 reviews the key
polymeric materials used in conductive adhesives and the analytic
approaches for ECA characterizations. Chapter 4 deals with the recent
advances in materials, processes, and applications of isotropically
conductive adhesives (ICAs), particularly focusing on the fundamental
understanding and improvement of materials properties for ICAs and
nano-ICAs. Chapter 5 discusses the recent development and applications
of anisotropically conductive adhesives (ACA) with the emphasis on the
nano-materials implementation for improved performance. Chapter 6
describes the latest materials and processing development of non-
conductive adhesives (NCA). Chapter 7 discusses the details of conductive
nano-inks and their applications in transparent electrodes, printed electronics,
and other packaging areas. Chapter 8 focuses on the recent research and
development of materials and applications of intrinsically conducting
polymers. And finally, Chapter 9 summarizes the recent advances of
conductive adhesives with nanotechnology and discusses the challenges and
opportunities for continuing the work on nanoconductive adhesives.
vi Preface
The field of electrically conductive adhesives and nanotechnology is quite
broad and their development is dynamic, so it is impossible to cover every
aspect of them. We have attempted to include most major areas with the
latest references which should be useful to our audience who work in this
vast growing discipline. With the advances of microelectronics packaging
and nanotechnology, there is always a constant need of improved materials
and technology. This is a challenge that requires the continuous and active
collaborative efforts between materials scientists, chemists, physicists,
device and package design engineers.

We express our gratitude to many of our colleagues and friends in the field
of microelectronics packaging, conductive adhesives and nanoscience and
nanotechnology. Many of their published works have been cited in this
book, including work published by many other experts in the fields. We
would also like to thank Owen Hildreth and Angela Duan for proofreading
some chapters and Steven Elliot and Andrew Leigh for editorial suggestions.

Chandler, AZ Yi Li

Yantai, China Daniel Lu
Atlanta, GA C.P. Wong
Contents

1 Introduction ..........................................................................................1
1.1 Electronics Packaging and Interconnect........................................1

1.2 Interconnection Materials............................................................11

1.2.1 Lead-Free Interconnect Materials....................................12
1.2.2 Electrically Conductive Adhesives..................................15
References............................................................................................19

2 Nanotechnology...................................................................................25
2.1 Introduction to Nanotechnologies and Nanopackaging..............25

2.2 Nanoparticles...............................................................................26

2.2.1 Introduction.....................................................................26
2.2.2 Nanoparticle Fabrication.................................................27
2.2.3 Nanoparticle Applications...............................................28
2.3 Nano Solder Particles..................................................................30

2.4 Carbon Nanotubes (CNTs)..........................................................38

2.4.1 Carbon Nanotubes for Electrical Interconnect
Applications....................................................................39
2.5 Nanocomposites..........................................................................48

2.5.1 Recent Advances in Nanocomposites.............................48
2.5.2 Areas of Application of Nanocomposites.......................51
2.6 Nano Interconnect.......................................................................53

2.6.1 Carbon Nanotube Transistors..........................................53
2.6.2 CNT Via..........................................................................54
2.6.3 CNT as Flip Chip Interconnect.......................................55
2.6.4 Nanoparticle Interlayer for Copper to Copper Bonding.......56
2.6.5 Interconnection Using Inkjet Printing of Nano-ink.........56
2.7 Nanowires and Nanobelts............................................................60

2.7.1 Introduction.....................................................................60
2.7.2 Applications of Nanowires..............................................60
References............................................................................................65

3 Characterizations of Electrically Conductive Adhesives.....................81
3.1 Recent Advances in Polymeric Materials for Electronic

Packaging....................................................................................81
3.1.1 Silicones (Polyorganosiloxanes).....................................81
3.1.2 Epoxies............................................................................83
3.1.3 Polyurethanes..................................................................84
3.1.4 Polyimides.......................................................................85
viii Contents
3.1.5 Silicone-Polyimide (SPI).................................................86
3.1.6 Bismaleimide (BMI) Resins............................................88
3.1.7 Cyanate Ester Resins.......................................................89
3.2 Analytical Approaches for ECA..................................................91

3.2.1 Differential Scanning Calorimeter (DSC).......................91
3.2.2 Thermogravimetry Analyzer (TGA)...............................95
3.2.3 Dynamic Mechanical Analyzer (DMA)..........................96
3.2.4 Thermo-mechanical Analysis (TMA).............................98
3.2.5 Viscometer and Rheometer...........................................100
3.2.6 Fourier Transform Infrared (FT-IR)..............................101
3.2.7 X-Ray Photoelectron Spectroscopy (XPS)....................103
3.2.8 X-Ray Diffraction (XRD).............................................104
3.2.9 Transmission Electron Microscopy (TEM)...................105
3.2.10 Scanning Electron Microscopy (SEM).........................106
3.2.11 Raman Spectroscopy....................................................107
3.2.12 Gas Chromatography/Mass Spectrometry....................109
3.2.13 Electrical Characterization of ECAs.............................110
3.2.14 Mechanical Property Characterization..........................113
References..........................................................................................117

4 Isotropically Conductive Adhesives (ICAs)......................................121
4.1 Introduction................................................................................121
4.1.1 Percolation Theory of Conduction................................121
4.1.2 Adhesive Matrix............................................................123
4.1.3 Conductive Fillers.........................................................124
4.2 Processing of ICAs....................................................................128

4.2.1 Screen and Stencil Printing...........................................129
4.2.2 Dispensing.....................................................................130
4.2.3 Inkjet Printing................................................................130
4.3 Flip Chip Applications Using ICAs..........................................132

4.3.1 ICA Process for Unbumped Chips................................132
4.3.2 Metal-Bumped Flip Chip Joints....................................138
4.4 ICAs for Surface Mount Applications.......................................140

4.5 ICAs for CSP Applications.......................................................141

4.6 ICAs for Advanced Packaging Applications.............................142

4.6.1 Solar Cell.......................................................................142
4.6.2 Three-Dimensional Stacking.........................................143
4.6.3 Microspring...................................................................144
4.7 ICAs for Printed Circuit Board Applications............................146

4.8 High-Frequency Performance of ICA Joints.............................148

4.9 Reliability of ICA Joints...........................................................149
Contents ix
4.10 Recent Advances on ICAs.........................................................152

4.10.1 Fundamental Understanding of the Lubricant Layer
on Ag Flakes................................................................152
4.10.2 Understanding of Conductivity Mechanism of ICAs.......166
4.10.3 Improvement of Electrical Conductivity of ICAs.......176
4.10.4 Mechanism Underlying Unstable Contact
Resistance of ICA Joints.............................................178
4.10.5 Improvement of Contact Resistance Stability.............189
4.10.6 Impact Performance....................................................200
4.10.7 Adhesion Strength.......................................................202
4.10.8 Recent Advances on Nano-ICAs.................................205
References..........................................................................................211

5 Anisotropically Conductive Adhesives/Films (ACA/ACF)..............227
5.1 Introduction...............................................................................227

5.2 ACA Materials and Processing.................................................228

5.2.1 ACA Materials..............................................................228
5.2.2 Processing.....................................................................229
5.3 Applications of ACA/ACF........................................................231

5.3.1 ACAs/ACFs for Flat Panel Displays ............................231
5.3.2 ACAs/ACFs for Fine-Pitch Interconnections................234
5.3.3 ACA/ACF in Flip Chip Applications............................235
5.4 Recent Advances of ACA/ACF and Nano-ACA/ACF.............237

5.4.1 Low-Temperature Sintering of Nano-Ag- Filled
ACA/ACF.....................................................................238
5.4.2 ACA Joints with Low Melting Point (LMP) Filler.......242
5.4.3 Self-Assembled Molecular Wires
for Nano-ACA/ACF......................................................244
5.4.4 Silver Migration Control in Nano-silver filled ACA....250
5.4.5 ACA/ACF with Ferromagnetic Conductive Fillers.......255
5.4.6 Nanowire ACF for Ultra-fine-pitch Flip
Chip Interconnection.....................................................259
5.4.7 Thermal Performance of ACA/ACF.............................260
5.5 ACA/ACF Reliability................................................................263

5.5.1 Effects of Bonding Conditions......................................264
5.5.2 Effect of Mechanical Properties on the
Reliability of ACF Joints..............................................264
5.5.3 Effects of Bump Height on the Reliability
of ACA Joints...............................................................267
5.6 Future Advances of ACA/ACF.................................................268

5.6.1 Materials Development.................................................268
x Contents
5.6.2 High-Frequency Compatibility.....................................268
5.6.3 Reliability......................................................................269
5.6.4 Wafer-Level Application...............................................269
References..........................................................................................271

6 Non-conductive Adhesives/Films (NCA/NCF).................................279
6.1 Introduction...............................................................................279

6.2 Electrical Properties of NCA/NCF Joints.................................281

6.2.1 Contact Resistance of NCA/NCF Joints.......................281
6.3 Reliability of NCA/NCF Joints.................................................285

6.4 Recent Advances of NCA/NCF................................................288

6.4.1 Low-Temperature Assembly of NCF ...........................288
6.4.2 Improvement of Electrical Properties of NCA/NCF
Joints with π-Conjugated Molecular Wires...................289
6.4.3 NCA/NCF with Fillers..................................................291
6.4.4 Incorporation of Non-conductive Fillers
in NCA/NCF.................................................................293
6.4.5 Multi-layer ACF/NCF...................................................294
6.4.6 Wafer-Level NCF..........................................................296
References..........................................................................................297

7 Conductive Nano-Inks.......................................................................303
7.1 Introduction...............................................................................303

7.1.1 An Overview of Conventional Patterning
of Electronics................................................................303
7.1.2 Introduction of Printed Electronics...............................305
7.1.3 Utility of High Volume Printing Processes
in Printable Electronics.................................................307
7.2 Conventional Conductive Inks..................................................312

7.2.1 Metallic Ink...................................................................313
7.2.2 Conductive Carbon Ink.................................................317
7.3 Conductive Nano-Inks...............................................................322

7.3.1 Metallic Nano-Inks........................................................322
7.3.2 Conducting Polymer - Based Inks.................................326
7.3.3 Organometallic Ink........................................................328
7.4 Processing of Nano Ink.............................................................332

7.4.1 Ink-jet Printing..............................................................332
7.4.2 Pyrolytic Printing..........................................................338
7.4.3 Gravure Printing............................................................341
7.5 Applications of Conductive Inks...............................................343

7.5.1 Die Attach for High Power Devices..............................343
Contents xi
7.5.2 Printed Low-resistance Metal Conductors for Printed
Electronics.....................................................................344
7.5.3 Micro-bump...................................................................347
7.5.4 Interconnect for System-in-Package (SiP)....................349
References..........................................................................................351

8 Intrinsically Conducting Polymers (ICPs).........................................361
8.1 Basics of Intrinsically Conducting Polymers............................361

8.1.1 Introduction...................................................................361
8.1.2 Doping...........................................................................365
8.1.3 Polyacetylene................................................................368
8.2 Applications of Conducting Polymers......................................369

8.2.1 Lithography...................................................................369
8.3 Metallization..............................................................................376

8.4 Corrosion Protection of Metals.................................................378

8.5 Electrostatic Discharge (ESD) Protection for Electronic

Components...............................................................................380
8.6 Field-Effect Transistors (FET)..................................................381

8.7 Sensors......................................................................................383

8.8 Microfluid Pump ......................................................................390

8.9 Shielding of Electromagnetic Interference (EMI)....................392

8.10 Nanofiber-Based Nanocomposites And Devices ....................393

8.11 Polymer Light-Emitting Diodes (PLEDs)................................396

8.12 Solar Cells................................................................................402

8.13 Three-Dimensional Interconnect..............................................404

8.14 Conducting Polymer Artificial Muscles...................................405

8.15 ICP as Interconnect Materials..................................................406

References..........................................................................................409

9 Future Trend of Conductive Adhesive Technology...........................425
9.1 Recent Advances in Conductive Adhesive Technology...........425

9.2 Challenges and Opportunities of ICAs......................................426

9.2.1 Electrical Performance Improvement............................426
9.2.2 Silver Migration............................................................426
9.2.3 Mechanical Property Improvement...............................427
9.2.4 Manufacturability and Yields........................................427
9.2.5 Cost Reduction..............................................................427
9.2.6 ICAs Based on Intrinsically Conducting Polymers.......428
9.2.7 ICAs for Printed Organic Electronics ..........................429
9.3 Challenges and Opportunities for ACAs...................................430

9.3.1 Thermo-mechanical Reliability.....................................430