Lead–free Solders – Materials Reliability for Electronics

Providing a viable alternative to lead-based solders is a major research thrust for the electrical and electronics industries - whilst mechanically compliant lead-based solders have been widely used in the electronic interconnects, the risks to human health and to the environment are too great to allow continued widescale usage. Lead-free Solders: Materials Reliability for Electronics chronicles the search for reliable drop-in lead-free alternatives and covers: * Phase diagrams and alloy development * Effect of minor alloying additions * Composite approaches including nanoscale reinforcements * Mechanical issues affecting reliability * Reliability under impact loading * Thermomechanical fatigue * Chemical issues affecting reliability * Whisker growth * Electromigration * Thermomigration Presenting a comprehensive understanding of the current state of lead-free electronic interconnects research, this book approaches the ongoing research from fundamental, applied and manufacturing perspectives to provide a balanced view of the progress made and the requirements which still have to be met.

Table of Contents:
Series Preface xv Preface xvii List of Contributors xix Thematic Area I: Introduction 1 1 Reliability of Lead-Free Electronic Solder Interconnects: Roles of Material and Service Parameters 3 K. N. Subramanian 1.1 Material Design for Reliable Lead-Free Electronic Solders Joints 3 1.2 Imposed Fields and the Solder Joint Responses that Affect Their Reliability 5 1.3 Mechanical Integrity 5 1.4 Thermomechanical Fatigue (TMF) 6 1.5 Whisker Growth 7 1.6 Electromigration (EM) 7 1.7 Thermomigration (TM) 8 1.8 Other Potential Issues 8 Thematic Area II: Phase Diagrams and Alloying Concepts 11 2 Phase Diagrams and Their Applications in Pb-Free Soldering 13 Sinn-wen Chen, Wojciech Gierlotka, Hsin-jay Wu, and Shih-kang Lin 2.1 Introduction 14 2.2 Phase Diagrams of Pb-Free Solder Systems 14 2.3 Example of Applications 23 2.4 Conclusions 39 3 Phase Diagrams and Alloy Development 45 Alan Dinsdale, Andy Watson, Ales Kroupa, Jan Vrestal, Adela Zemanova, and Pavel Broz 3.1 Introduction 45 3.2 Computational Thermodynamics as a Research Tool 48 3.3 Thermodynamic Databases the Underlying Basis of the Modelling of Phase Diagrams and Thermodynamic Properties, Databases for Lead-Free Solders 51 3.4 Application of the SOLDERS Database to Alloy Development 57 3.5 Conclusions 68 4 Interaction of Sn-based Solders with Ni(P) Substrates: Phase Equilibria and Thermochemistry 71 Clemens Schmetterer, Rajesh Ganesan, and Herbert Ipser 4.1 Introduction 72 4.2 Binary Phase Equilibria 73 4.3 Ternary Phase Equilibria Ni-P-Sn 85 4.4 Thermochemical Data 94 4.5 Relevance of the Results and Conclusion 111 Thematic Area III: Microalloying to Improve Reliability 119 5 'Effects of Minor Alloying Additions on the Properties and Reliability of Pb-Free Solders and Joints' 121 Sung K. Kang 5.1 Introduction 122 5.2 Controlling Ag3Sn Plate Formation 125 5.3 Controlling the Undercooling of Sn Solidification 132 5.4 Controlling Interfacial Reactions 136 5.5 Modifying the Microstructure of SAC 145 5.6 Improving Mechanical Properties 149 5.7 Enhancing Electromigration Resistance 151 5.8 Summary 153 6 Development and Characterization of Nano-composite Solder 161 Johan Liu, Si Chen, and Lilei Ye 6.1 Introduction 162 6.2 Nano-composite Solder Fabrication Process 162 6.3 Microstructure 166 6.4 Physical Properties 167 6.5 Mechanical Properties 169 6.6 Challenges and Solutions 171 6.7 Summary 174 Thematic Area IV: Chemical Issues Affecting Reliability 179 7 Chemical Changes for Lead-Free Soldering and Their Effect on Reliability 181 Laura J. Turbini 7.1 Introduction 181 7.2 Soldering Fluxes and Pastes 181 7.3 Cleaning 185 7.4 Laminates 185 7.5 Halogen-Free Laminates 186 7.6 Conductive Anodic Filament (CAF) Formation 189 7.7 Summary 193 Thematic Area V: Mechanical Issues Affecting Reliability 195 8 Influence of Microstructure on Creep and High Strain Rate Fracture of Sn-Ag-Based Solder Joints 197 P. Kumar, Z. Huang, I. Dutta, G. Subbarayan, and R. Mahajan 8.1 Introduction 198 8.2 Coarsening Kinetics: Quantitative Analysis of Microstructural Evolution 199 8.3 Creep Behavior of Sn-Ag-Based Solders and the Effect of Aging 206 8.4 Role of Microstructure on High Strain Rate Fracture 219 8.5 Summary and Conclusions 227 9 Microstructure and Thermomechanical Behavior Pb-Free Solders 233 D.R. Frear 9.1 Introduction 233 9.2 Sn-Pb Solder 234 9.3 Pb-Free Solders 237 9.4 Summary 248 10 Electromechanical Coupling in Sn-Rich Solder Interconnects 251 Q.S. Zhu, H.Y. Liu, L. Zhang, Q.L. Zeng, Z.G. Wang, and J.K. Shang 10.1 Introduction 252 10.2 Experimental 253 10.3 Results 255 10.4 Discussion 264 10.5 Conclusions 269 11 Effect of Temperature-Dependent Deformation Characteristics on Thermomechanical Fatigue Reliability of Eutectic Sn-Ag Solder Joints 273 Andre Lee, Deep Choudhuri, and K.N. Subramanian 11.1 Introduction 274 11.2 Experimental Details 275 11.3 Results and Discussion 276 11.4 Summary and Conclusions 294 Thematic Area VI: Whisker Growth Issues Affecting Reliability 297 12 Sn Whiskers: Causes, Mechanisms and Mitigation Strategies 299 Nitin Jadhav and Eric Chason 12.1 Introduction 299 12.2 Features of Whisker Formation 303 12.3 Understanding the Relationship between IMC Growth, Stress and Whisker Formation 308 12.4 Summary Picture of Whisker Formation 314 12.5 Strategies to Mitigate Whisker Formation 316 12.6 Conclusion 318 13 Tin Whiskers 323 Katsuaki Suganuma 13.1 Low Melting Point Metals and Whisker Formation 323 13.2 Room-Temperature Tin Whiskers on Copper Substrate 325 13.3 Thermal-Cycling Whiskers on 42 Alloy/Ceramics 326 13.4 Oxidation/Corrosion Whiskers 329 13.5 Mechanical-Compression Whiskers in Connectors 330 13.6 Electromigration Whiskers 331 13.7 Whisker Mitigation 332 13.8 Future Work 334 Thematic Area VII: Electromigration Issues Affecting Reliability 337 14 Electromigration Reliability of Pb-Free Solder Joints 339 Seung-Hyun Chae, Yiwei Wang, and Paul S. Ho 14.1 Introduction 339 14.2 Failure Mechanisms of Solder Joints by Forced Atomic Migration 342 14.3 IMC Growth 351 14.4 Effect of Sn Grain Structure on EM Reliability 363 14.5 Summary 366 15 Electromigration in Pb-Free Solder Joints in Electronic Packaging 375 Chih Chen, Shih-Wei Liang, Yuan-Wei Chang, Hsiang-Yao Hsiao, Jung Kyu Han, and K.N. Tu 15.1 Introduction 376 15.2 Unique Features for EM in Flip-Chip Pb-Free Solder Joints 376 15.3 Changes of Physical Properties of Solder Bumps During EM 386 15.4 Challenges for Understanding EM in Pb-Free Solder Microbumps 393 15.5 Thermomigration of Cu and Ni in Pb-Free Solder Microbumps 394 15.6 Summary 394 16 Effects of Electromigration on Electronic Solder Joints 401 Sinn-wen Chen, Chih-ming Chen, Chao-hong Wang, and Chia-ming Hsu 16.1 Introduction 401 16.2 Effects of Electromigration on Solders 402 16.3 Effects of Electromigration on Interfacial Reactions 408 16.4 Modeling Description of Effects of Electromigration on IMC Growth 414 16.5 Conclusions 418 Thematic Area VIII: Thermomigration Issues Affecting Reliability 423 17 Thermomigration in SnPb and Pb-Free Flip-Chip Solder Joints 425 Tian Tian, K.N. Tu, Hsiao-Yun Chen, Hsiang-Yao Hsiao, and Chih Chen 17.1 Introduction 425 17.2 Thermomigration in SnPb Flip-Chip Solder Joints 427 17.3 Thermomigration in Pb-Free Flip-Chip Solder Joints 432 17.4 Driving Force of Thermomigration 435 17.5 Coupling between Thermomigration and Creep 439 17.6 Coupling between Thermomigration and Electromigration: Thermoelectric Effect on Electromigration 441 17.7 Summary 441 Thematic Area IX: Miniaturization Issues Affecting Reliability 443 18 Influence of Miniaturization on Mechanical Reliability of Lead-Free Solder Interconnects 445 Golta Khatibi, Herbert Ipser, Martin Lederer, and Brigitte Weiss 18.1 Introduction 445 18.2 Effect of Miniaturization on Static Properties of Solder Joints (Tensile and Shear) 448 18.3 Creep and Relaxation of Solder Joints 475 18.4 Summary and Conclusions 478 References 482 Index 487

About the Author :
K. N. Subramanian is Professor of Materials Science and Engineering at Michigan State University. He has been a full-time faculty member at MSU for over 45 years. For the last 15 years he has devoted all his research efforts to lead-free electronic solders.