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CONDUCTIVE ADHESIVES FOR ELECTRONICS PACKAGING

Edited by Johan Liu

Pages--431+xv; Tables--38; Figures--329; References--457.
ISBN 0 901150 37 1

Code: EP36

Contents of this page:

Description
About the Editor
Table of Contents

Description

This book presents state-of-the-art knowledge of conductive adhesive joining technology in various electronics packaging applications.

It is divided into four parts. Firstly, the book gives an introduction to conductive adhesives and joining technologies. Secondly, several chapters deal with fundamental issues of materials selection and manufacturing, processing, conduction mechanisms and contact reliability theories associated with the use of conductive adhesives. Both isotropically and anisotropically conductive adhesives are included. After these the book focuses on the various applications using conductive adhesives such as in surface mount, die-attach, display and flip-chip. Finally, the toxicity and environmental health aspects are investigated.

‘Conductive Adhesives for Electronics Packaging’ can be used as a reference book for design, production and quality engineers, decision makers and research scientists who are, or wish to be, engaged in electronics packaging research and development using conductive adhesive joining technology.

About the Editor

Johan Liu received his masters degree in materials science and engineering from the Royal Institute of Technology, Stockholm, Sweden in 1984. He also received his PhD there in 1989 in the area of rapid solidification technology. He has been with IVF since 1989. As a member of the management team for the IVF Electronics Packaging Research Division, he is responsible for the research of interconnection technology at IVF and runs a number of multi-client research programmes including conductive adhesive joining, chip-on-board and lead-free solders. He is also docent in the Chalmers University of Technology, Gšteborg, Sweden, where he supervises and teaches PhD students.

Dr Liu serves as the European editor of the Journal of Electronics Manufacturing, is vice chairman of the technical committee of the international conference on ‘adhesives in electronics’, a member of the international programme liaison committee for the Interpack'97 Conference, European liaison chair for the American VLSI Computer and System Packaging Workshop and general chair of the first IEEE International Symposium on Polymeric Electronics Packaging. He is a senior member of IEEE, a member of ISHM and The Institute of Welding and Materials Research Society. He also chairs the IEEE CPMT Sweden Chapter. He has presented a number of invited papers and tutorials at international conferences in the area of conductive adhesive joining technology and has twice been guest editor for the Journal of Electronics Manufacturing.

Recently Dr Liu received the best paper award 1996 from the IEEE Transactions of CPMT, Part B: Advanced Packaging, for a paper entitled ‘Anisotropically conductive adhesive flip-chip bonding on rigid and flexible printed circuit substrates’, and he has received numerous awards throughout his career for work and leadership involving conductive adhesives in electronics packaging.

Table of Contents

CHAPTER ONE

Introduction to Conductive Adhesive Joining Technology

1.1 Introduction

1.2 Adhesive Types

1.2.1 Isotropic Conductive Adhesives

1.2.2 Bi-directional Anisotropic Conductive Adhesives

1.2.3 Unidirectional Anisotropic Conductive Adhesives

1.2.4 Patterned Anisotropic Conductive Adhesives

1.2.5 Non-conductive Adhesives

1.3 Materials

1.3.1 Polymer Binders for Conductive Adhesives

1.3.2 Thermoplastics

1.3.3 Thermosets

1.3.4 Thermoset Vs Thermoplastic

1.3.5 Radiation Curable Systems

1.3.6 Conductive Fillers

1.3.6.1 Silver-based Conductors

1.3.6.2 Copper

1.3.6.3 Nickel

1.3.6.4 Carbon

1.3.6.5 Metal-coated Particles

1.4 Applications for Conductive Adhesives

1.5 Future Possibilities

1.5.1 Intrinsically Conductive Polymers (ICPs)

1.5.2 Polymer Bonding

CHAPTER TWO

Cationic Cure of Epoxy Resins and UV Options for Conductive Adhesives

2.1 Introduction

2.2 Advantages of UV Curability

2.3 Cationic Epoxy Chemistry

2.4 The Polyol Component

2.5 Initiators for Cationic Chemistry

2.6 Conductive Fillers

2.7 Dual Cure Adhesive Systems

2.8 Pre-assembly Irradiation Technique

2.9 Adhesive Properties

2.10 Application Examples

2.11 Summary

CHAPTER THREE

Conduction Mechanisms and Microstructure Development in Isotropic, Electrically Conductive Adhesives

3.1 Introduction

3.2 ICA Structures

3.3 Microstructural Cure Effects

3.4 Metal Particle Impedance

3.5 Interparticulate Impedances

3.6 ICA Contact Effects

3.7 Percolation Theory

3.8 Theoretical Modelling

3.9 Experimental Studies

3.10 Conclusions

3.11 Acknowledgments

CHAPTER FOUR

Models to Determine Guidelines for the Anisotropic Conducting Adhesives Joining Process

4.1 Introduction

4.2 A Simple Model of Fluid Flow during Assembly

4.2.1 Navier-Stokes Equations

4.2.2 Stefan’s Equation

4.3 Refinements to the basic model

4.3.1 The Scott Equation

4.3.2 The Effects of Non-flat Surfaces

4.3.3 Model Verification

4.4 Opens and Bridging Between Pads

4.4.1 Opens

4.4.2 Bridging

4.5 Summary

4.6 Acknowledgements

CHAPTER FIVE

Curing of Isotropic Electrically Conductive Adhesives

5.1 Introduction

5.2 Adhesive Cure

5.3 Experimental Results

5.4 Conclusions

CHAPTER SIX

Contact Reliability Modelling and Material Behaviour of Conductive Adhesives under Thermomechanical Loads

6.1 Introduction

6.2 Electro-Thermo-Mechanical Responses of Anisotropic Conductive Adhesive Materials

6.2.1 Deformation Analysis

6.2.2 Force-Resistance Relationship

6.2.2.1 Elasto-Plastic Solutions

6.2.3 Non-Linear Stress-Strain Relationship

6.2.4 In-Plane Effective Coefficient of Thermal Expansion and Thermal Stress

6.2.5 Discussion

6.3 Process Induced Residual Stresses in Isotropic Conductive Adhesive (ICA) Joints

6.3.1 Thermomechanical Material Properties Characterisation for Conductive Adhesives

6.3.2 Viscoelastic Behaviour of Conductive Adhesives

6.3.3 Finite Element Model

6.3.4 Discussion

6.4 High Frequency Characterisation of Conductive Adhesive Joints under Mechanical and Thermomechanical Loading

6.4.1 Experimental Procedures

6.4.2 Experimental Results

6.4.3 Discussions

CHAPTER SEVEN

Design and Modelling of Solder-filled ACAs for Flip-chip and Flexible Circuit Applications

7.1 Introduction

7.2 Conductive Adhesives

7.3 Metallurgy of microsoldering

7.3.1 Non-reactive and Reactive Wetting

7.3.2 Energetics and Kinetics of Microsoldering

7.4 Solder fillers for Z-adhesives

7.4.1 Reactive Bonding of Cu Conductors with SnBi-filled Adhesive

7.4.2 Non-reactive Bonding of Sn-coated Cu Conductors with SnBi-filled Adhesive

7.4.3 SnPb-bumped Flip Chips Bonded on FR-4 with Bi Particle-filled Adhesive

7.5 Reliability Results

7.6 Solder-Filled Adhesives in Flip-Chip Applications

7.7 Conclusions

CHAPTER EIGHT

Recent Advances and Evaluation of Anisotropically Conductive Adhesives for Microelectronics Assembly

8.1 Introduction

8.2 Materials and Conduction Mechanisms

8.3 ACA Assembly

8.4 Techniques for Extremely Fine Pitch Applications

8.5 Characterisation Of ACAs

8.6 Reliability Of ACA Interconnections

8.7 Conclusions

8.8 References

CHAPTER NINE

Manufacturability, reliability and failure mechanisms in conductive adhesive joining for flip-chip and surface mount applications

9.1 Introduction

9.2 Concerns with Solder Joints

9.3 Necessary Conditions for a Good Conductive Adhesive Joint

9.4 Microstructures of Various Conductive Adhesives

9.5 The Effect of Curing Degree on the Joint Reliability

9.6 Manufacturability and Process Flow for Conductive Adhesive Joining

9.7 Inspection

9.8 Repair

9.9 Failure Mechanisms

9.9.1 Oxidation/Hydration

9.9.1.1 Sn37pb Surface

9.9.1.2 Cu Surface

9.9.1.3 Theoretical Treatment of Oxidation and Crack Growth

9.9.2 Polymer Degradation due to Moisture Attack

9.10 Reliability and Quality of the ACA Flip-chip Joint

9.10.1.1 The Effect of Bonding Pressure, Particle Size and Bump Geometry

9.10.1.1.1 Qualitative Analysis of the Criteria for a Good ACA Joint

9.10.1.2 Effect of the Temperature Ramp Rate

9.10.1.3 Effect of Bonding Pressure Distribution

9.10.1.3.1 Factors Affecting Pressure Distribution During Bonding

9.10.1.4 Effect of Electrical Design

9.10.1.5 Effect of Bump Uniformity

9.10.1.6 Effect of Board Planarity

9.11 High Frequency Properties

9.11.1 FR-4

9.11.2 High-frequency Duroid Substrate

9.12 Thermal Resistance of Conductive Adhesive Joint in Flip-chip Application

9.13 Issues and Concerns

9.13.1 Prediction Methodology for Estimation of Real Service Life after Accelerated Testing

9.13.2 Bending Performance

9.14 Development Trends in ACA Conductive Adhesive Joining

9.15 Conclusions

9.16 Acknowledgements

CHAPTER TEN

Anisotropic Conductive Adhesive Films for Flip-Chip Interconnection

10.1 Introduction

10.2 Principles Of ACF Interconnection

10.3 Materials

10.3.1 Adhesives

10.3.2 Conducting Particles

10.4 Approaches for Very Fine Pitch Interconnections

10.5 Flip-Chip Interconnection to Organic Substrates13-14

10.5.1 Flip-Chip Interconnection with Bumped Chips

10.5.2 Flip-Chip Interconnection with Bumpless Chips to Various Organic Substrates

10.6 Conclusion

10. 7 Acknowledgement

CHAPTER ELEVEN

Reliability of Electrically Conductive Adhesive Joints in Surface Mount Applications

11.1 Introduction

11.2 Isotropic Conductive Adhesive Systems

11.2.1 Epoxies

11.2.2 Polyimides45

11.2.3 Silicones47,48

11.2.4 Electroconductive Ag-filled Acrylates

11.2.5 Thermoplastic Adhesives

11.3 Reliability Investigations

11.3.1 Test Conditions

11.3.2 Results at Munich University (Orthmann, Habenicht)

11.3.3 Reliability Investigations at IVF

11.3.4 Reliability Investigations at Philips and TNO

11.3.5 Biased Temperature/Humidity Testing

11.3.6 Investigations at Binghampton

11.3.7 Reliability Results with Epoxies and Silicone Adhesives from a Nordic Project

11.3.8 Reliability Investigations by a US Consortium — Drop Tests

11.3.9 Miscellaneous Other Investigations

11.4 Failure Mechanisms

11.4.1 Oxidation and Corrosion

11.4.2 Crack Formation

11.4.3 Depletion of Silver in Surface Layer of Adhesive

11.4.4 Creep Effects in the Adhesive Layer

11.4.5 Formation of an Intermetallic Layer

11.4.6 Ag Migration

11.5 Conclusions

11.6 Acknowledgement

CHAPTER TWELVE

Electrically Conductive Joints using Non-Conductive Adhesives (NCAs) in Surface Mount Applications

12.1 Introduction and Literature Review

12.1.1 Literature Review

12.2 NCA Joining and Theory of Contact Formation

12.3 Applications in Fine-Pitch Surface Mount Technology

12.3.1 Materials and Manufacturing Process

12.3.2 Morphology and Electrical Properties of the Joints

12.3.3 Reliability

12.3.4 Summary

12.4 Investigations of the Conduction Mechanism

12.4.1 Voltage and Temperature Characteristics

12.4.2 Analysis of Fracture Surfaces

12.4.3 Model for the Conduction Mechanism

12.5 High Current and Thermal Properties

12.5.1 Experimental Set-up

12.5.2 Effects of High Current Load

12.5.3 Temperature Dependence of Contact Resistance

12.5.4 Visualisation of Hot Spots

12.5.5 Summary

12.6 Concluding Remarks

CHAPTER THIRTEEN

Use of Conductive Adhesives as Die-Attach For Power Electronics Applications

13.1 Introduction

13.2 Thermal Conductivity of Adhesives

13.3 Thermal Resistance of Adhesive Joints

13.4 Thermal Stress in Adhesive Joints

13.5 Cracking, Delamination and Thermal Fatigue of Adhesive Joints

13.6 Design and Optimisation of Die Attach

CHAPTER FOURTEEN

Replacing Solder with Isotropically Conductive Adhesives in Die Bonding of Power Semiconductors

14.1 Isotropically Conductive Adhesives

14.2 Comparing Adhesive Die Bonding with Soldering

14.2.1 Adhesion and mechanical properties

14.2.2 Electrical and thermal conductivity

14.2.3 Processing

14.2.4 Cost approximation

14.2.5 Environmental considerations

14.3 Power Semiconductor Die Bonding with Isotropically Conductive Adhesives

14.4 Experimental Results from Replacing Solder with Isotropically Conductive Adhesives

14.4.1 Test adhesives

14.4.2 Manufacturing test module

14.4.3 Electrical effects of replacing solder with isotropically conductive adhesives

14.4.4 Thermal effects of replacing solder with isotropically conductive adhesives

14.5 Reliability Aspects of Replacing Solder with Isotropically Conductive Adhesives

14.5.1 Reliability in thermal and operational cycling

14.5.2 Reliability in elevated humidity and temperature ageing

14.5.3 Analysing test adhesive reliability

14.6 Conclusions

CHAPTER FIFTEEN

Overview of Display Conductive Adhesive Interconnection Technologies

15.1 Introduction

15.2 LCD Construction

15.2.1 Driver IC packaging

15.3 Adhesives for LCD Driver Connection

15.3.1 Anisotropic Conductive Adhesive

15.3.1.1 ACA Particle Distribution

15.3.1.2 Bonding Parameters

15.3.2 Isotropic Conductive Adhesive

15.3.3 Non-conductive Adhesive

15.3.3.1 Chip on Flex (TAB)

15.4 Chip on Glass Technology

15.4.1 General Discussion

15.4.1.1 Process and Reliability

15.4.2 Flip Chip on Glass with Anisotropic Conductive Adhesive

15.4.2.1 Seiko: ‘Maple Method’

15.4.2.2 Casio: ‘Microconnector’

15.4.2.3 Oki: ACF With Au Bumps

15.4.2.4 Hitachi: ‘Double-Layer Acf’

15.4.2.5 Samsung: Dielectric Dams

15.4.2.6 Sumitomo: ‘VIS’

15.4.3 Flip Chip on Glass with Isotropic Conductive Adhesive

15.4.3.1 Citizen: ‘Plated Bumps with Isotropic Adhesive’

15.4.3.2 Matsushita: ‘Stud (Wire) Bumps’

15.4.3.3 Philips

15.4.4 Flip Chip on Glass with Non-conductive Adhesive

15.4.4.1 Matsushita: ‘Micro Bump-Bonding’

15.4.4.2 Sharp: ‘Elastic’

15.4.4.3 Seiko Epson: ‘Un-Bumped Dies’, With Conductive Particles on the Glass Electrodes

15.4.4.4 Mitsubishi: Photo Process Of Conductive Particles

15.4.5 Non-adhesive COG Technologies

15.4.5.1 cog-end

15.5 Reliability

15.5.1 Failure Mechanisms

15.5.2 Reliability Testing

15.6 Future

CHAPTER SIXTEEN

Integration of Microsystems using Flip-Chip Technologies and Adhesives

16.1 Introduction

16.2 Motivation for Stacking

16.3 Interconnections

16.4 Various Bonding Methods

16.4.1 Bump Processing

16.4.2 Adhesives — Conductive/Non-conductive

16.4.2.1 Non-Conductive Adhesive

16.4.2.2 Conductive Adhesives

16.5 Topologies

16.6 Conclusion

16.7 Acknowledgement

CHAPTER SEVENTEEN

Adhesives and Health Hazards

17.1 Introduction

17.2 Factors Influencing Chemical Health Hazards

17.2.1 Intrinsic health hazardous properties of the adhesive

17.2.2 Extent of exposure

17.2.3 Duration and frequency of Exposure

17.3 Ways of Exposure

17.4 What do we Actually Know about Health Hazards with Different Substances?

17.5 How can Different Substances affect Health

17.6 What do Adhesives Contain?

17.7 Health Hazards Associated with Epoxy Adhesives

17.7.1 How to Choose Epoxy Adhesive — Recommendations

17.7.2 Monomers and Prepolymers

17.7.3 Curing Agents in Epoxy Adhesives

17.7.4 Reactive Diluents

17.8 Health Hazards Associated with Acrylic Adhesives

17.8.1 How to Choose Acrylic Adhesive — Recommendations

17.8.2 Monomers and Prepolymers

17.9 Health Hazards Associated with Polyurethane Adhesives

17.9.1 How to Choose Polyurethane Adhesive — Recommendations

17.9.2 Monomers and Prepolymers

17.9.3 Prepolymerised Isocyanates

17.9.4 Polyurethanes

17.10 Environmental Aspects of Adhesives

CHAPTER EIGHTEEN

Health and Environmental Aspects of Conductive Adhesives — The Use of Lead-Based Alloys Compared with Adhesives

18.1 Introduction

18.2 Adhesives or Solder?

18.3 Scope of the Problem — Lead Consumption in Soldering

18.3.1 Suppliers of Soldering Materials

18.3.2 Quantitative Analysis

18.3.3 Substitution Potential

18.4 The Method

18.5 Chemical Groups of Adhesives

18.5.1 Epoxy Adhesives

18.5.2 Working with Epoxies — Hazards Identification

18.5.3 Epoxy Adhesives and the Environment

18.6 Substitution of the Soldering Process

18.7 Environmental Comparison & Recommendations to Users of Conductive Adhesives

18.8 Acknowledgements

 

 

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 Page last revised 11.02.05

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